Biochemical and molecular characterization of neonicotinoids resistance in the tarnished plant bug, Lygus lineolaris

In the southern United States, neonicotinoids are commonly applied as foliar insecticides to control sucking insect pests, such as the tarnished plant bug (TPB, Lygus lineolaris). In this study, spraying bioassays were conducted to determine the toxicity of five neonicotinoids and sulfoxaflor to susceptible and late fall field-collected TPB adults from Mississippi Delta region. Compared to a susceptible population, the field-collected TPBs exhibited the highest resistance to imidacloprid (up to 19.5-fold), a moderate resistance to acetamiprid (9.43-fold), clothianidin (13.68-fold), thiamethoxam (7.88-fold) and the least resistance to thiacloprid (4.61-fold) and sulfoxaflor (1.82-fold), respectively. A synergist study demonstrated that piperonyl butoxide (PBO) significantly increased the toxicity of imidacloprid and thiamethoxam by 22.2- and 15.3-fold, respectively, while triphenyl phosphate (TPP) and diethyl maleate (DEM) only showed 2-3-fold synergism to both neonicotinoids. In the field-collected TPBs, activities of the three detoxification enzymes esterase, glutathione S-transferase (GST) and CYP450 monooxygenase (P450) were significantly increased by 3.43-, 1.48- and 2.70-fold, respectively, when compared to the susceptible population. Additionally, after 48 h exposure to imidacloprid or thiamethoxam, resistant TPB adults exhibited elevated esterase activities, decreased GST activities, and no significant changes in P450 activities. Further examinations revealed that the expression of certain esterase and P450 detoxification genes were significantly elevated in resistant TPBs. Overall, these results suggest that elevated esterase and P450s expression and enzyme activity are key mechanisms for metabolic resistance in TPBs to neonicotinoids. Our findings also provide valuable information for selection and adoption of neonicotinoid insecticides for resistance management of TPBs and minimizing toxic risk to foraging bees.

Discovery of a new highly pathogenic toxin involved in insect sepsis

IMPORTANCE

As a current biocontrol resource, entomopathogenic nematodes and their symbiotic bacterium can produce many toxin factors to trigger insect sepsis, having the potential to promote sustainable pest management. In this study, we found Steinernema feltiae and Xenorhabdus bovienii were highly virulent against the insects. After infective juvenile injection, Galleria mellonella quickly turned black and softened with increasing esterase activity. Simultaneously, X. bovienii attacked hemocytes and released toxic components, resulting in extensive hemolysis and sepsis. Then, we applied high-resolution mass spectrometry-based metabolomics and found multiple substances were upregulated in the host hemolymph. We found extremely hazardous actinomycin D produced via 3-hydroxyanthranilic acid metabolites. Moreover, a combined transcriptomic analysis revealed that gene expression of proteins associated with actinomycin D was upregulated. Our research revealed actinomycin D might be responsible for the infestation activity of X. bovienii, indicating a new direction for exploring the sepsis mechanism and developing novel biotic pesticides.

The nitrogen-dependent GABA pathway of tomato provides resistance to a globally invasive fruit fly

Introduction

The primary metabolism of plants, which is mediated by nitrogen, is closely related to the defense response to insect herbivores.

Methods

An experimental system was established to examine how nitrogen mediated tomato resistance to an insect herbivore, the oriental fruit fly (Bactrocera dorsalis). All tomatoes were randomly assigned to the suitable nitrogen (control, CK) treatment, nitrogen excess (NE) treatment and nitrogen deficiency (ND) treatment.

Results

We found that nitrogen excess significantly increased the aboveground biomass of tomato and increased the pupal biomass of B. dorsalis. Metabolome analysis showed that nitrogen excess promoted the biosynthesis of amino acids in healthy fruits, including γ-aminobutyric acid (GABA), arginine and asparagine. GABA was not a differential metabolite induced by injury by B. dorsalis under nitrogen excess, but it was significantly induced in infested fruits at appropriate nitrogen levels. GABA supplementation not only increased the aboveground biomass of plants but also improved the defensive response of tomato.

Discussion

The biosynthesis of GABA in tomato is a resistance response to feeding by B. dorsalis in appropriate nitrogen, whereas nitrogen excess facilitates the pupal weight of B. dorsalis by inhibiting synthesis of the GABA pathway. This study concluded that excess nitrogen inhibits tomato defenses in plant-insect interactions by inhibiting GABA synthesis, answering some unresolved questions about the nitrogen-dependent GABA resistance pathway to herbivores.

Early Season Monitoring of Tarnished Plant Bug, Lygus lineolaris, in Wild Hosts Using Pheromone Traps

The tarnished plant bug, Lygus lineolaris (Hemiptera: Miridae), has a wide host range of over 700 plant species, including 130 crops of economic importance. During early spring, managing the field edges with weeds and other wild hosts is important in preventing early-season infestations of L. lineolaris in cotton to prevent damage to the squares and other fruiting structures. Scouting fields for L. lineolaris is time- and labor-intensive, and end-user variability associated with field sampling can lead to inaccuracies. Insect traps that combine visual cues and pheromones are more accurate, sustainable, and economically feasible in contrast to traditional insect detection methods. In this study, we investigated the application of red or white sticky cards baited with the female-produced sex pheromone to monitor overwintering L. lineolaris populations in early spring. Field experiments demonstrated that the red sticky cards baited with a pheromone blend containing hexyl butyrate, (E)-2-hexenyl butyrate, and (E)-4-oxo-2-hexenal in 4:10:7 ratio are highly effective in trapping L. lineolaris adults in early spring before the row crops are planted, and in monitoring their movement into a cotton crop. The monitoring of L. lineolaris should help growers to make judicious decisions on insecticide applications to control early pest infestations, thereby reducing economic damage to cotton.

Chemical Communication in Insects: New Advances in Integrated Pest Management Strategies

Chemical communication plays a pivotal role in many insect behaviors, including food-seeking, recruitment, the recognition of congeners, reproduction, alarm, territorial marking, and survival [...].

The mechanisms of metabolic resistance to pyrethroids and neonicotinoids fade away without selection pressure in the tarnished plant bug Lygus lineolaris

BACKGROUND

Heavy selection pressure prompted the development of resistance in a serious cotton pest tarnished plant bug (TPB), Lygus Lineolaris in the mid-southern United States. Conversely, a laboratory resistant TPB strain lost its resistance to five pyrethroids and two neonicotinoids after 36 generations without exposure to any insecticide. It is worthwhile to examine why the resistance diminished in this population and determine whether the resistance fade away has practical value for insecticide resistance management in TPB populations.

RESULTS

A field-collected resistant TPB population in July (Field-R1) exhibited 3.90-14.37-fold resistance to five pyrethroids and two neonicotinoids, while another field-collected TPB population in April (Field-R2) showed much lower levels of resistance (0.84-3.78-fold) due to the absence of selection pressure. Interestingly, after 36 generations without exposure to insecticide, the resistance levels in the same population [laboratory resistant strain (Lab-R)] significantly decreased to 0.80-2.09-fold. The use of detoxification enzyme inhibitors had synergistic effects on permethrin, bifenthrin and imidacloprid in resistant populations of Lygus lineolaris. The synergism was more pronounced in Field-R2 than laboratory susceptible (Lab-S) and Lab-R TPB population. Moreover, esterase, glutathione S-transferase (GST), and cytochrome P450-monooxygenases (P450) enzyme activities increased significantly by approximately 1.92-, 1.43-, and 1.44-fold in Field-R1, respectively, and 1.38-fold increased P450 enzyme activities in Field-R2 TPB population, compared to the Lab-S TPB. In contrast, the three enzyme activities in the Lab-R strain were not significantly elevated anymore relative to the Lab-S population. Additionally, Field-R1 TPB showed elevated expression levels of certain esterase, GST and P450 genes, respectively, while Field-R2 TPB overexpressed only P450 genes. The elevation of these gene expression levels in Lab-R expectedly diminished to levels close to those of the Lab-S TPB populations.

CONCLUSION

Our results indicated that the major mechanism of resistance in TPB populations was metabolic detoxification, and the resistance development was likely conferred by increased gene expressions of esterase, GST, and P450 genes, the fadeaway of the resistance may be caused by reversing the overexpression of esterase, GST and P450. Without pesticide selection, resistant gene (esterase, GST, P450s) frequencies declined, and detoxification enzyme activities returned to Lab-S level, which resulted in the recovery of the susceptibility in the resistant TPB populations. Therefore, pest's self-purging of insecticide resistance becomes strategically desirable for managing resistance in pest populations. Published 2023. This article is a U.S. Government work and is in the public domain in the USA.

Biocontrol effect of entomopathogenic fungi Metarhizium anisopliae ethyl acetate-derived chemical molecules: An eco-friendly anti-malarial drug and insecticide

Insect pests represent a major threat to human health and agricultural production. With a current over-dependence on chemical insecticides in the control of insect pests, leading to increased chemical resistance in target organisms, as well as side effects on nontarget organisms, the wider environment, and human health, finding alternative solutions is paramount. The employment of entomopathogenic fungi is one such potential avenue in the pursuit of greener, more target-specific methods of insect pest control. To this end, the present study tested the chemical constituents of Metarhizium anisopliae fungi against the unicellular protozoan malaria parasite Plasmodium falciparum, the insect pests Anopheles stephensi Listen, Spodoptera litura Fabricius, and Tenebrio molitor Linnaeus, as well as the nontarget bioindicator species, Eudrilus eugeniae Kinberg. Fungal crude chemical molecules caused a noticeable anti-plasmodial effect against P. falciparum, with IC50 and IC90 values of 11.53 and 7.65 µg/mL, respectively. The crude chemical molecules caused significant larvicidal activity against insect pests, with LC50 and LC90 values of 49.228-71.846 µg/mL in A. stephensi, 32.542-76.510 µg/mL in S. litura, and 38.503-88.826 µg/mL in T. molitor at 24 h posttreatment. Based on the results of the nontarget bioassay, it was revealed that the fungal-derived crude extract exhibited no histopathological sublethal effects on the earthworm E. eugeniae. LC-MS analysis of M. anisopliae-derived crude metabolites revealed the presence of 10 chemical constituents. Of these chemicals, three major chemical constituents, namely, camphor (15.91%), caprolactam (13.27%), and monobutyl phthalate (19.65%), were highlighted for potential insecticidal and anti-malarial activity. The entomopathogenic fungal-derived crude extracts thus represent promising tools in the control of insect pests and malarial parasites.

A chromosome scale assembly of the tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), genome

OBJECTIVE

The tarnished plant bug (TPB), Lygus lineolaris (Palisot de Beauvois) (Hemiptera: Miridae), is a pest damaging many cultivated crops in North America. Although partial transcriptome data are available for this pest, a genome assembly was not available for this species. This assembly of a high-quality chromosome-length genome of TPB is aimed to develop the genetic resources that can provide the foundation required for advancing research on this species.

RESULTS

The initial genome of TPB assembled with paired-end nucleotide sequences generated with Illumina technology was scaffolded with Illumina HiseqX reads generated from a proximity ligated (HiC) library to obtain a high-quality genome assembly. The final assembly contained 3963 scaffolds longer than 1 kbp to yield a genome of 599.96 Mbp. The N50 of the TPB genome assembly was 35.64 Mbp and 98.68% of the genome was assembled into 17 scaffolds larger than 1 Mbp. This megabase scaffold number is the same as the number of chromosomes observed in karyotyping of this insect. The TPB genome is known to have high repetitive DNA content, and the reduced assembled genome size compared to flowcytometric estimates of approximately 860 Mbp may be due to the collapsed assembly of highly similar regions.

Combining visual cues and pheromone blends for monitoring and management of the tarnished plant bug Lygus lineolaris (Hemiptera: Miridae)

BACKGROUND

The tarnished plant bug Lygus lineolaris (Palisot de Beauvois) is considered the most damaging pest of cotton (Gossypium hirsutum L.) in the mid-southern United States. Previous studies have reported the role of different ratios of volatile metathoracic gland components such as hexyl butyrate, (E)-2-hexenyl butyrate and (E)-4-oxo-2-hexenal in eliciting low-level attraction of L. lineolaris. In this study, we tested different visual cues (colored sticky cards) in combination with olfactory cues (pheromone blends) to optimize the attraction and capture of L. lineolaris in the field.

RESULTS

Red-colored sticky cards were more attractive to L. lineolaris adults than white, blue or yellow cards. Red sticky cards combined with blends of three potential pheromone components attracted significantly more L. lineolaris adults than sticky cards without a blend added. Traps baited with a blend of hexyl butyrate, (E)-2-hexenyl butyrate and (E)-4-oxo-2-hexenal in 4:10:7 ratio, respectively, caught a significantly higher number of L. lineolaris than those baited with 10:4:2 or 7:10:4 blends or an unbaited control in the first week of the experiment.

CONCLUSIONS

Combining visual cues (red color) with olfactory cues (pheromone blends) significantly increased the capture of L. lineolaris in the field. This device or a future iteration could contribute towards sustainable and environmentally appropriate early-season monitoring and management of L. lineolaris in the field. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Lethal Concentration and Sporulation by Contact and Direct Spray of the Entomopathogenic Fungus Beauveria bassiana on Different Stages of Nezara viridula (Heteroptera: Pentatomidae)

The southern green stink bug, Nezara viridula (L.) (Heteroptera: Pentatomidae) is the most significant pest of soybean worldwide. The present study was conducted to compare the effectiveness of a Delta native strain NI8 of Beauveria bassiana by contact and direct spray on nymphs (2nd to 5th instar) and adults of N. viridula. Water control and four concentrations of B. bassiana were used to evaluate the survival, mortality, and molting percentage and to estimate median lethal concentration (LC50), median lethal sporulation (LS50), and resistance ratio (RR50). Direct spray at all concentrations observed the greatest reduction in survival on all life stages. Mortality and sporulation were positively correlated by concentration, while molting was highly variable with a significantly lower negative correlation on insects that were directly sprayed. Pathogenicity exhibited reduction as young stages developed and emerged to adult. The LC50 (Contact: 612 spores/mm2; Direct spray: 179 spores/mm2) and LS50 (Contact: 1960 spores/mm2 Spray: 3.3 × 106) values showed that adults of N. viridula were highly resistant than any other life stage when exposed to either contact or direct spray. Fourth instar was the most susceptible (LC50: Contact: 18 spores/mm2; Direct spray: 23 spores/mm2) (LS50: Contact: 53 spores/mm2; Direct spray: 26 spores/mm2) followed by second, third, and fifth instars.

Capturing Wheat Phenotypes at the Genome Level

Recent technological advances in next-generation sequencing (NGS) technologies have dramatically reduced the cost of DNA sequencing, allowing species with large and complex genomes to be sequenced. Although bread wheat (Triticum aestivum L.) is one of the world's most important food crops, efficient exploitation of molecular marker-assisted breeding approaches has lagged behind that achieved in other crop species, due to its large polyploid genome. However, an international public-private effort spanning 9 years reported over 65% draft genome of bread wheat in 2014, and finally, after more than a decade culminated in the release of a gold-standard, fully annotated reference wheat-genome assembly in 2018. Shortly thereafter, in 2020, the genome of assemblies of additional 15 global wheat accessions was released. As a result, wheat has now entered into the pan-genomic era, where basic resources can be efficiently exploited. Wheat genotyping with a few hundred markers has been replaced by genotyping arrays, capable of characterizing hundreds of wheat lines, using thousands of markers, providing fast, relatively inexpensive, and reliable data for exploitation in wheat breeding. These advances have opened up new opportunities for marker-assisted selection (MAS) and genomic selection (GS) in wheat. Herein, we review the advances and perspectives in wheat genetics and genomics, with a focus on key traits, including grain yield, yield-related traits, end-use quality, and resistance to biotic and abiotic stresses. We also focus on reported candidate genes cloned and linked to traits of interest. Furthermore, we report on the improvement in the aforementioned quantitative traits, through the use of (i) clustered regularly interspaced short-palindromic repeats/CRISPR-associated protein 9 (CRISPR/Cas9)-mediated gene-editing and (ii) positional cloning methods, and of genomic selection. Finally, we examine the utilization of genomics for the next-generation wheat breeding, providing a practical example of using in silico bioinformatics tools that are based on the wheat reference-genome sequence.

A nondestructive method of calculating the wing area of insects

Most insects engage in winged flight. Wing loading, that is, the ratio of body mass to total wing area, has been demonstrated to reflect flight maneuverability. High maneuverability is an important survival trait, allowing insects to escape natural enemies and to compete for mates. In some ecological field experiments, there is a need to calculate the wing area of insects without killing them. However, fast, nondestructive estimation of wing area for insects is not available based on past work. The Montgomery equation (ME), which assumes a proportional relationship between leaf area and the product of leaf length and width, is frequently used to calculate leaf area of plants, in crops with entire linear, lanceolate leaves. Recently, the ME was proved to apply to leaves with more complex shapes from plants that do not have any needle leaves. Given that the wings of insects are similar in shape to broad leaves, we tested the validity of the ME approach in calculating the wing area of insects using three species of cicadas common in eastern China. We compared the actual area of the cicadas’ wings with the estimates provided by six potential models used for wing area calculation, and we found that the ME performed best, based on the trade‐off between model structure and goodness of fit. At the species level, the estimates for the proportionality coefficients of ME for three cicada species were 0.686, 0.693, and 0.715, respectively. There was a significant difference in the proportionality coefficients between any two species. Our method provides a simple and powerful approach for the nondestructive estimation of insect wing area, which is also valuable in quantifying wing morphological features of insects. The present study provides a nondestructive approach to estimating the wing area of insects, allowing them to be used in mark and recapture experiments.

Chromosome length genome assembly of the redbanded stink bug, Piezodorus guildinii (Westwood)

OBJECTIVE

The redbanded stink bug (RBSB), Piezodorus guildinii (Hemiptera: Pentatomidae), is native to the Caribbean Basin and is currently considered an invasive pest in Florida, Louisiana, Mississippi, and Texas in the southern United States. Although RBSB is an economically important invasive pest in the USA, relatively few studies have been conducted to understand molecular mechanisms, population genetic structure, and the genetic basis of resistance to insecticides. The objective of this work was to obtain a high-quality genome assembly to develop genomic resources to conduct population genetic, genomic, and physiological studies of the RBSB.

RESULTS

The genome of RBSB was sequenced with Pacific Biosciences technology followed by two rounds of scaffolding using Chicago libraries and HiC proximity ligation to obtain a high-quality assembly. The genome assembly contained 800 scaffolds larger than 1 kbp and the N50 was 170.84 Mbp. The largest scaffold was 222.22 Mbp and 90% of the genome was included in the 7 scaffolds larger than 118 Mbp. The number of megabase scaffolds also matched the number of chromosomes in this insect. The genome sequence will facilitate the development of resources to conduct studies on genetics, transcriptomics, and physiology of RBSB.

Monitoring of Mutual Interference Behavior of Trichogramma brassicae (Hymenoptera: Trichogrammatidae) over 45 Generations of Rearing on Angoumois Grain Moth

Trichogramma brassicae (Bezdenko) is one of the most common species of natural enemies used in augmentative biological control programs in many countries. Understanding of the foraging behavior of a parasitoid can help us to improve its performance under field conditions. This study is the first assessment of trends in mutual interference behavior of T. brassicae under long-term mass rearing (over 45 generations) on a common factitious host, Sitotroga cerealella (Olivier). Our results revealed that the total parasitism rate of T. brassicae reared on S. cerealella eggs was significantly affected by parasitoid densities and number of generations under continuous rearing. Also, parasitoid density and number of generations in rearing had significant effects on the per capita parasitism rate. Meanwhile, per capita searching efficiencies were different in sequential generations and at different densities. The number of hosts parasitized per parasitoid decreased on day 1 of the experiment with increasing parasitoid density, showing the effect of mutual interference. The linear regression between the natural logarithm of per capita searching efficiency and the natural logarithm of parasitoid density showed an inverse relationship. While the m (interference coefficient) values increased, the Q (quest constant) values had a decreasing trend over 45 generations. The highest (- 0.167) and lowest (- 0.242) values of m were observed in G45 and G5, respectively. Accordingly, G5 and G45 had the highest (0.053) and lowest (0.023) Q values, respectively. Thus, it seems the negative effects of mutual interference decreased over generations.

Binary and ternary toxicological interactions of clothianidin and eight commonly used pesticides on honey bees (Apis mellifera)

Although many toxicological evaluations have been conducted for honey bees (Apis mellifera), most of these studies have only focused on the effects of individual chemicals. However, honey bees are usually exposed to pesticide mixtures under field conditions. In this study, we examined the effects of individual pesticides and mixtures of clothianidin (CLO) with eight other pesticides [carbaryl (CAR), thiodicarb (THI), chlorpyrifos (CHL), beta-cyfluthrin (BCY), gamma-cyhalothrin (GCY), tetraconazole (TET), spinosad (SPI) and indoxacarb (IND)] on honey bees using a feeding method. Toxicity tests of a 4-day exposure to individual pesticides revealed that CLO had the highest toxicity to A. mellifera, with an LC₅₀ value of 0.24 μg a.i. mL^-1, followed by IND and CHL with LC₅₀ values of 3.40 and 3.56 μg a.i. mL^-1, respectively. SPI and CAR had relatively low toxicities, with LC₅₀ values of 7.19 and 8.42 μg a.i. mL^-1, respectively. In contrast, TET exhibited the least toxicity, with an LC₅₀ value of 258.7 μg a.i. mL^-1. Most binary mixtures of CLO with other pesticides exerted additive and antagonistic effects. However, all the ternary mixtures containing CLO and TET (except for CLO+TET+THD) elicited synergistic responses to bees. Either increased numbers of components in the mixture or/and a unique mode of action appeared to be responsible for the higher toxicity of mixtures. Our findings emphasized the need for risk assessment of pesticide mixtures rather than the individual chemicals. Our data also provided information that might help growers avoid increased toxicity and unnecessary injury to pollinators.

Biology, Ecology, and Pest Management of the Tarnished Plant Bug, Lygus lineolaris (Palisot de Beauvois) in Southern Row Crops

Simple Summary

The tarnished plant bug, Lygus lineolaris, is a polyphagous, sap-feeder that causes significant economic damage in several field crops, especially cotton (Gossypium hirsutum L.) in the mid-southern United States. In 2020, it was reported that 4.8 million acres of cotton were infested by Lygus spp. in the United States. A broad host range, polyphagous feeding behavior and high mobility of this pest along with resistance development to conventional pesticides helped them establish as a significant pest of concern for cotton growers in the mid-south. Since the publication of a review by Layton (2000) on damage caused by Lygus lineolaris, many new research studies have been published on the Lygus biology, ecology, and integrated pest management strategies. A comprehensive review paper that summarizes these latest research developments and Lygus management strategies will be useful for researchers and cotton growers. In this review, we report and discuss the latest developments in Lygus research and the new control strategies that have been developed in the last two decades.

Abstract

The tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), (Hemiptera: Miridae) is considered the most damaging pest of cotton (Gossypium hirsutum L.) in the mid-southern United States, although it is established throughout the United States, southern Canada, and northern Mexico. The introduction of transgenic crops for the control of moths in the Heliothine complex and eradication of the boll weevil, Anthonomus grandis, from much of the United States led to greatly reduced pesticide use in cotton fields, which allowed L. lineolaris to emerge as a new primary pest of cotton in the mid-southern United States. Since the publication of a review by Layton (2000) on damage caused by Lygus lineolaris, many new studies have been published on the changes in host range, population dynamics, sampling methods and thresholds, cultural practices, sex pheromones and attractant blends, novel pesticides and insecticide resistance mechanisms, olfactory and feeding behaviors, introduction of biological control agents, host-plant resistance mechanisms, and new molecular and genetic tools for integrated pest management of Lygus species in cotton and other important crops. Here, we review and discuss the latest developments in L. lineolaris research in the last two decades.

Development of a Method for Rearing Nezara viridula (Heteroptera: Pentatomidae) on a Semi-solid Artificial Diet

A method for rearing the southern green stinkbug, (Nezara viridula L.) (Heteroptera: Pentatomidae), using a modified lygus semi-solid artificial diet was developed. First to second-instar nymph were reared in a density of 631.5 ± 125.05 eggs per Petri-dish (4 cm deep × 15 cm diam). Second instar to adult were reared in a density of 535.0 ± 112.46 s instar nymphs per rearing cage (43 × 28 × 9 cm). Mating and oviposition occurred in popup rearing cages (30 × 30 cm), each holding 60-90 mixed sex adults of similar age. Adults emerged 35.88 ± 2.13 d after oviposition and survived for an average of 43.09 ± 9.53 d. On average, adults laid 223.95 ± 69.88 eggs in their lifetime, for a total production of 8,099 ± 1,277 fertile eggs/oviposition cage. Egg fertility was 77.93% ± 16.28. Egg masses held in petri-dishes had a total hatchability of 79.38% ± 20.03. Mortality of early nymphs in petri-dishes was 0.64% ± 0.12 for the first instar and 1.37% ± 0.45 for second instar. Late nymphal mortality in rearing cages was 1.41% ± 0.10, 3.47% ± 1.27, and 4.72% ± 1.29 for the third, fourth, and fifth instars, respectively. Survivorship from nymphs to adults was 88.48% ± 2.76. Using artificial diet for rearing N. viridula could reduce cost by avoiding time-consuming issues with daily feeding fresh natural hosts and insect manipulation. It could increase reliability and simplicity of bug production, which should facilitate mass rearing of its biological control agents.

Plant Volatiles and Oviposition Behavior in the Selection of Barley Cultivars by Wheat Stem Sawfly (Hymenoptera: Cephidae)

Wheat stem sawfly, [Cephus cinctus (Hymenoptera: Cephidae)], females display complex behaviors for host selection and oviposition. Susceptible hollow stem wheat (Triticum aestivum L.) cultivars release a greater amount of attractive compound, (Z)-3-hexenyl acetate and receive a greater number of eggs compared to resistant solid stem wheat cultivars. However, barley (Hordeum vulgare L.) is becoming a more common host for C. cinctus in Montana. Therefore, how do host selection and oviposition behaviors on barley cultivars compare to what happens when encountering wheat cultivars? To answer this question, we carried out greenhouse experiments using two barley cultivars: 'Hockett' and 'Craft'. Between these cultivars at Zadoks stages 34 and 49, we compared host selection decisions using a Y-tube olfactometer, compared oviposition behaviors on stems, and counted the number of eggs inside individual stems. In Y-tube bioassays, we found a greater number of C. cinctus females were attracted to the airstream passing over 'Hockett' than 'Craft' barley cultivars. Although the frequencies of oviposition behaviors were similar between these cultivars, the number of eggs was greater in 'Hockett'. Volatile profiles indicated that the amount of linalool was greater in the airstream from 'Craft' than in 'Hockett' at Zadoks 34 while the amount of (Z)-3-hexenyl acetate was greater in airstream from 'Hockett' at both Zadoks 34 and 49. These results suggest that volatiles of barley plants influenced host selection behavior of ovipositing C. cinctus females, while other discriminating behaviors do not differ between cultivars.

Biocontrol of Wireworms (Coleoptera: Elateridae) Using Entomopathogenic Nematodes: The Impact of Infected Host Cadaver Application and Soil Characteristics

Wireworms have become a significant menace to cereals in the Northern Great Plains. Therefore, research toward developing effective control methods such as biological control with entomopathogenic nematodes (EPNs) is warranted. Two strains, each of two EPN species, Steinernema carpocapsae (Weiser) and Steinernema riobrave Cabanillas, Poinar, and Raulston in the form of infected Galleria mellonella (L.) cadavers were evaluated against wireworms in field and greenhouse. In field experiments, none of the four EPN strains were found effective against wireworms. However, in the greenhouse test, three of the strains, S. carpocapsae (All and Cxrd) or S. riobrave (355) applied in cadavers killed 50-68% of the sugarbeet wireworm, Limonius californicus (Mannerheim) was associated with 8-24% plant damage at 35 d after treatment (DAT), when seeds were treated with imidacloprid. The mortality range was 40-56% with 57-75% plant damage observed at 35 DAT, when seeds were planted without imidacloprid treatment. Synergistic effect among imidacloprid and S. carpocapsae (Cxrd) or S. riobrave (355) was observed in regard to L. californicus mortality. Additionally, effects of soil texture, moisture, and temperature on the infection rate of EPNs against L. californicus were examined in the laboratory. Limonius californicus mortality was not significantly affected by either soil moisture or soil types maintained at field capacity moisture levels. However, soil temperature showed a significant effect on L. californicus mortality. Overall, imidacloprid enhanced the infection and killing ability of EPNs against L. californicus and S. carpocapsae (All and Cxrd) strains were the virulent strains in different soil experiments.

Effects of Age, Phase Variation and Pheromones on Male Sperm Storage in the Desert Locust, Schistocerca gregaria

Simple Summary

We investigated male sperm storage in the desert locust Schistocerca gregaria. Phase (solitary or gregarious) did not affect sperm distribution in the vas deferens and seminal vesicle, whereas sperm accumulation of the seminal vesicle in gregarious locusts was promoted more than in solitary ones. Pheromones received from neither mature adults nor nymphs affected sperm distribution in the vas deferens and seminal vesicle. However, sperm accumulation in the seminal vesicle was more promoted in the gregarious locusts which received pheromones from mature adults than those obtained from nymphs at early adult stage, especially seven days after adult emergence.

Abstract

In general, sperm produced in the testis are moved into the seminal vesicle via the vas deferens in insects, where they are stored. How this sperm movement is controlled is less well understood in locusts or grasshoppers. In this study, the effects of age, phase variation and pheromones on male sperm storage were investigated in the desert locust, Schistocerca gregaria (Forskål). In this locust, a pair of ducts, the vasa deferentia, connect the testes to a pair of the long, slender seminal vesicles that are folded approximately thirty times, and where the sperm are stored. We found that phase variation affected the level of sperm storage in the seminal vesicle. Moreover, adult males that detected pheromones emitted by mature adult males showed enhanced sperm storage compared with males that received the pheromones emitted from nymphs: The former, adult male pheromones are known to promote sexual maturation of immature adults of both sexes, whereas the latter, nymphal pheromones delay sexual maturation. Most mature adult males had much sperm in the vasa deferentia at all times examined, suggesting daily sperm movement from the testes to the seminal vesicles via the vasa deferentia. As adult males aged, sperm were accumulated from the proximal part to the distal end of the seminal vesicle. Many sperm remained in the seminal vesicle after mating. These results suggest that young or new sperm located near the proximal part of the seminal vesicle could be used for mating, whereas old sperm not used for mating are stored in the distal part of the seminal vesicle.

Latest Developments in Insect Sex Pheromone Research and Its Application in Agricultural Pest Management

Since the first identification of the silkworm moth sex pheromone in 1959, significant research has been reported on identifying and unravelling the sex pheromone mechanisms of hundreds of insect species. In the past two decades, the number of research studies on new insect pheromones, pheromone biosynthesis, mode of action, peripheral olfactory and neural mechanisms, and their practical applications in Integrated Pest Management has increased dramatically. An interdisciplinary approach that uses the advances and new techniques in analytical chemistry, chemical ecology, neurophysiology, genetics, and evolutionary and molecular biology has helped us to better understand the pheromone perception mechanisms and its practical application in agricultural pest management. In this review, we present the most recent developments in pheromone research and its application in the past two decades.

Generation-Dependent Functional and Numerical Responses of a Naturally Fungus-Infected Colony of Habrobracon hebetor (Hymenoptera: Braconidae) Reared on Ephestia kuehniella (Lepidoptera: Pyralidae) in Iran

The functional and numerical responses of Habrobracon hebetor (Say) were assessed over 30 sequential generations (G) on different densities (2, 4, 8, 16, 32, 64, and 128 fifth-instar larvae) of the Mediterranean flour moth, Ephestia kuehniella (Zeller). Seven tested generations (G2inf, G4inf, G6inf, G8inf, G10inf, G15inf, and G30inf) had already been naturally infected by a fungus species, whereas only the second generation (G2) had the colonies of both infected (G2inf) and uninfected (G2uninf) individuals. All infected generations, as well as the uninfected generation, showed a Type III functional response. A high variation was found in the handling times (Th) of the parasitoid through 30 sequential generations, and G10inf had the longest handling time. The shortest handling time and the maximum estimated attack rate (T/Th) were observed in G2inf. No significant difference in terms of the number of parasitized hosts was found among all infected generations, as well as between G2inf and G2uninf. Although the handling times in G2inf and G2uninf were close to each other, the attack coefficient of G2uninf was more than that of G2inf. The attack coefficient and handling time of infected generations increased from G2inf to G10inf and then decreased in the higher generations. The most plausible parameters of functional response of infected generations were observed in Ginf. A negative relationship between eggs laid and host densities was observed in the infected generations (G2inf, G4inf, G6inf, G8inf, and G10inf). G2uninf and, among infected generations, Ginf were the best generations for practical utilization in inundative release programs.

Quality control of the parasitoid wasp Trichogramma brassicae (Hymenoptera: Trichogrammatidae) over 45 generations of rearing on Sitotroga cerealella

Trichogramma brassicae (Bezdenko) is an important biological control agent that has been used widely against many lepidopteran pests. Commonly, colonies of Trichogramma are mass reared on factitious hosts such as Sitotroga cerealella (Olivier) over many generations. In this study, we evaluated the quality and performance of a colony of T. brassicae that had been reared for over 45 generations (G) using two-sex life table parameters and parasitism capacity. We found that female adult longevity was significantly different among sequential generations, ranging from 5.58 ± 2.5 d (at G5) to 3.75 ± 1.42 d (at G45). However, no significant difference was found in male adult longevity among different generations. Although female wasps survived longer until the 15th generation, they allocated more days for egg laying at G5 and G10. The highest values of gross reproductive rate (GRR), net reproductive rate (R0 ), intrinsic rate of increase (r), finite rate of increase (λ) and mean generation time (T) were found in G5 and G10, which also showed significantly higher c0 . No significant difference in the finite parasitism rate (ω) was found among generations up to G15. These results suggest that T. brassicae wasps held under continuous laboratory rearing can be used successfully in biological control programs until the 15th generation without any loss of quality or performance. However, laboratory mass rearing colonies declined in quality after 15 generations and we suggest that they should be rejuvenated regularly by adding field-collected parasitoids periodically.

Characterization of the spatial distribution of alfalfa weevil, Hypera postica, and its natural enemies, using geospatial models

BACKGROUND

Understanding the spatio-temporal dynamics of prey and predator distributions can provide valuable insights into pest management strategies and conservation of natural enemies in agro-ecosystems. The alfalfa weevil, Hypera postica (Gyllenhal), is an economically important pest of alfalfa throughout the western United States. Coccinellids and nabids are among the most important natural enemies of this species, contributing to the biological control of H. postica in alfalfa fields. The spatio-temporal dynamics of H. postica and these two predator groups were investigated using 81 (= 9 × 9 grid) sample points in each of five alfalfa fields in north-central Montana. The data were analyzed using variogram and spatial analysis by distance indices (SADIE).

RESULTS

Variogram analysis revealed the spatial dependence (aggregation) of H. postica in 17 of 19 sampling times for larvae, and three of 12 sampling times for adults. Using SADIE, statistically significant aggregation distribution was evident in four of 19 sampling times for larvae, and five of 12 sampling times for adults of H. postica. Combined variogram and SADIE showed strong evidence of spatial aggregation of H. postica larval population (~95%) while a moderate level of aggregation in the adult population (~67%) of the sampling times analyzed. The average aggregation distances based on the range value of the variogram were 22.3 m and 14.7 m for larvae and adults, respectively. Based on variogram results, populations of natural enemies, coccinellids and Nabis spp. were found spatially aggregated in 57.9% and 5.6% of the sampling times, respectively. SADIE further supported the variogram results as coccinellid populations (52.6% of sampling times) were highly aggregated in contrast with the Nabis spp. populations (5.6% of sampling times) in alfalfa fields. There was no evidence of significant spatial synchrony between H. postica and its predators, coccinellids and Nabis spp.

CONCLUSION

Our study was able to determine the spatial and temporal distribution of H. postica and its two natural enemies (coccinellids and nabids) in irrigated alfalfa fields. The possible implications of these findings for integrated pest management (IPM) of alfalfa weevil populations are discussed.

Use of Taxonomic and Trait-Based Approaches to Evaluate the Effect of Bt maize Expressing Cry1Ie Protein on Non-Target Collembola: A Case Study in Northeast China

Simple Summary

Bt crops have been planted globally since the first commercial Bt maize was cultivated in the United States in 1996. Bt protein from Bt crops can be released to the soil and may potentially affect the non-target soil fauna. Collembola are one of the three most ubiquitous and abundant soil fauna, they have been widely used as indicators of environmental pollution, IE09S034 is a new cry1Ie maize breed independently developed by China, and Northeast China is the most important location for maize production in China. Therefore, this study aimed to clarify whether non-target soil Collembola were influenced by the cultivation of cry1Ie maize in Northeast China. Our results showed that maize variety had no significant effects on collembolan abundance, diversity, and morphological trait, indicating that two years cultivation of cry1Ie maize does not have a bad influence on Collembola in Northeast China.

Abstract

To evaluate the effect of Bt maize expressing Cry1Ie protein on non-target soil Collembola, a two-year field study was conducted in Northeast China. Bt maize line IE09S034 and its near isoline Zong 31 were selected as experimental crops; we investigated the collembolan community using both taxonomic and trait-based approaches, and elucidated the relationship between environmental variables and the collembolan community using redundancy analysis (RDA).The ANOVA results showed that maize variety neither had significant effect on the parameters based on taxonomic approach (abundance, species richness, Shannon–Wiener index, Pielou’s evenness index), nor on the parameters based on trait-based approach (ocelli number, body length, pigmentation level, and furcula development) in either year. The results of RDA also showed that maize variety did not affect collembolan community significantly. These results suggest that two years cultivation of cry1Ie maize does not affect collembolan community in Northeast China.

Effect of age on insecticide susceptibility and enzymatic activities of three detoxification enzymes and one invertase in honey bee workers (Apis mellifera)

Honey bee is an economically important insect for honey production and pollination. Frequent exposure to toxic pesticides is one of the major risk factors causing the pollinator population decline. However, age effects of honey bees on pesticide susceptibility have been largely ignored and many researchers use bees of unknown age for assessing the risk of pesticides. Honey bee workers are known to go through physiological and behavioral changes in order to differentiate different phenotypes to perform specific duties over their natural lifetime of 6 weeks or longer. In this study, we provide multi-parameter evidences of unignorable age effects of honey bee workers and suggest using a standard bee age to produce reliable and comparable data when assessing variable and realistic situations of in-hive and field exposures to pesticides. Using honey bee workers aged 4- to 42-days old, we examined susceptibility of the bees to five different insecticides from five different classes and measured enzymatic activities of three major detoxification enzymes and an invertase involved in honey production. Results showed gradual increase of natural mortality and decrease of soluble protein content in bees over the age span from 4 days to 42 days. Significant increases of mortality after separate treatments of five different insecticides confirmed drastic age effects of bees over the assessed age span. As they aged, honey bees also showed a gradual increase of cytochrome P450 oxidase activity while still maintaining constant levels of two other detoxification enzymes (esterase and glutathione S-transferase) and an invertase responsible for honey production.

Montana Native Entomopathogenic Nematode Species Against Limonius californicus (Coleoptera: Elateridae)

Wireworms are destructive soil inhabiting polyphagous pests in the Pacific Northwest and Intermountain region of the United States. Continuously increasing wireworm populations and damage in small grain crops such as spring wheat in Northern Great Plains has become a challenge for growers. Due to unavailability of effective control measures, alternative methods, including biological control agents such as entomopathogenic nematodes (EPNs) are needed. Native/indigenous EPN species are expected to have better potential than exotic species to control the local insect pests. Two Montana native EPN species (Steinernema feltiae and Heterorhabditis bacteriophora) were tested against, Limonius californicus (Coleoptera: Elateridae) in laboratory and shade house studies. In the laboratory bioassay, two isolates of S. feltiae at the rate of 28,000 IJs/five larvae killed 48-50% of the insects within 4 wk. Heterorhabditis bacteriophora was not able to cause >30% L. californicus larval mortality. None of the two isolates of S. feltiae performed well against L. californicus when tested in different soil types. Similarly, two isolates of S. feltiae that were tested killed only 20-25% wireworms in a shade house trial that did not differ significantly from the control treatment. Four weeks after EPN treatment in the shade house trial, the percentage of wheat plant damage from L. californicus ranged from 30 to 40% in the presence of S. felitae, not differing statistically from control. These results suggest that S. felitae have limited potential in managing wireworm populations.

Multiple decrement life tables of Cephus cinctus Norton (Hymenoptera: Cephidae) across a set of barley cultivars: The importance of plant defense versus cannibalism

Accurately estimating cause-specific mortality for immature insect herbivores is usually difficult. The insects are exposed to abiotic and biotic mortality factors, causing cadavers to simply disappear before cause of mortality can be recorded. Also, insect herbivores are often highly mobile on hosts, making it difficult to follow patterns for individuals through time. In contrast, the wheat stem sawfly, Cephus cinctus Norton, spends its entire egg, larval, and pupal period inside a host stem. Therefore, with periodic sampling stage-specific causes of mortality can be ascertained. Consequently, we examined C. cinctus mortality in eight barley, Hordeum vulgare L., cultivars in two locations in Montana from 2016 to 2018 by collecting stem samples from stem elongation to crop maturity at weekly intervals, and collecting overwintered barley stubs the following spring and summer from the same plots. If larvae were present, we examined larval status—dead or alive—and categorized dead individuals into one of 5 mortality categories: plant defense, cannibalism, parasitism, pathogens, and unknown factors. We used multiple decrement life tables to estimate cause-specific mortality and irreplaceable mortality (the proportion of mortality from a given cause that cannot be replaced by other causes of mortality). Plant defense (antibiosis) caused 85.7 ± 3.6%, cannibalism (governed by antixenosis) caused 70.1 ± 7.6%, parasitism caused 13.8 ± 5.9%, unknown factors caused 38.5 ± 7.6%, and pathogens caused 14.7 ± 8.5% mortality in the presence of all causes of mortality. Similarly, irreplaceable mortality due to plant defense was 22.3 ± 6.4%, cannibalism was 29.1± 4.2%, unknown factors was 6.2 ± 1.8%, pathogens was 0.9 ± 0.5%, and parasitism was 1. 5 ± 0. 6%. Antibiosis traits primarily killed newly emerged larvae, while other traits supported more favorable oviposition decisions by females, increasing mortality by obligate cannibalism. Our results suggest that breeding barley for resistance to C. cinctus targeting both categories of traits (antibiosis and antixenosis) is a highly valuable tactic for management of this important pest.

Effect of Precipitation and Temperature on Larval Survival of Cephus cinctus (Hymenoptera: Cephidae) in Barley Cultivars

Host plant traits strongly affect survivorship of insect herbivores, and host suitability is especially important for the wheat stem sawfly, Cephus cinctus Norton, which spends its entire egg, larval, and pupal periods in a single stem. Measuring larval survival inside stems from egg hatch through diapause-mediated dormancy is a potential measure of population size for the next year but is also useful in assessing effects of growing season precipitation and temperature. Larval growth is synchronized with host plant growth, and the larva cannot switch hosts. Thus, incorporating plant physiological time, as growing degree days (GDD), may yield a better prediction of larval survival. Therefore, we assessed wheat stem sawfly survival from early larval growth to the beginning of autumnal diapause in barley cultivars selected from across feed, forage, and two- or six-row malt groups. Field experiments were conducted in Gallatin and Chouteau counties, Montana, in 2016 and 2017. We used Kaplan-Meier estimation to assess larval survival among cultivars. We found that the survival of pre-diapause larvae was greatest in 'Hockett' (36.5%) and lowest in 'Celebration' (15.4%). Precipitation and temperature during the growing season affected temporal patterns for larval survival across study sites. Adjusting survivorship curves using site-specific GDD accumulation allowed cultivar-specific survivorship to be estimated more precisely for each site, despite differing environmental influences. Our findings suggest that measuring wheat stem sawfly survival across barley cultivars and standardizing by site-specific GDDs may provide better recommendations on barley cultivars that impede wheat stem sawfly population growth and reduce economic losses.

Optimization of Nitrogen Fertilizer Application Enhances Biocontrol Function and Net Income

The intensive use of nitrogen fertilizer has been a common approach for pursuing higher crop yields. However, the ecological effects of such use on the tritrophic interactions (crop-insect pest-natural enemy) and on the ecological and economic benefits of such use are poorly understood. Here, we investigated the effects of low, medium, and high levels of nitrogen fertilizer inputs (70, 140, and 280 kg/ha/yr) on cereal aphid (Sitobion avenae Fabricius [Hemiptera: Aphididae], Schizaphis graminum Rondani [Hemiptera: Aphididae], and Rhopalosiphum padi L. [Hemiptera: Aphididae]) abundance, primary parasitism rates, crop yield, and net income in winter wheat (Triticum aestivum [Poales: Poaceae] cv. Zhou 22) for 2 yr. A higher input of nitrogen fertilizer significantly enhanced the abundance of cereal aphids, while their primary parasitism rates (26.9 ± 3.5% in 2018 and 24.9 ± 4.5% in 2019) were highest at the medium nitrogen level. The performance of participants in the wheat-aphids-parasitoids system was likewise mediated by the nitrogen fertilizers. Meanwhile, wheat yield significantly increased with moderate increases in the nitrogen level, although overuse of nitrogen fertilizer did not significantly further enhance wheat yield. Finally, we found either low or overuse of nitrogen fertilizers resulted in lower net income than did medium nitrogen fertilization. These results demonstrate the need to reevaluate and adjust fertilizer use to optimize the eco-economic and sustainable management of agroecosystems.

Antixenosis, Antibiosis, and Potential Yield Compensatory Response in Barley Cultivars Exposed to Wheat Stem Sawfly (Hymenoptera: Cephidae) Under Field Conditions

Wheat stem sawfly, Cephus cinctus Norton, is an economically serious pest of cereals grown in North America. Barley cultivars were previously planted as resistant crops in rotations to manage C. cinctus, but due to increasing levels of injury to this crop, this is no longer a valid management tactic in Montana. Therefore, we aimed to understand antixenosis (behavioral preference), antibiosis (mortality), and potential yield compensation (increased productivity in response to stem injuries) in barley exposed to C. cinctus. We examined these traits in eight barley cultivars. Antixenosis was assessed by counting number of eggs per stem and antibiosis was assessed by counting infested stems, dead larvae, and stems cut by mature larvae. Potential yield compensation was evaluated by comparing grain yield from three categories of stem infestation: 1) uninfested, 2) infested with dead larva, and 3) infested cut by mature larva at crop maturity. We found the greatest number of eggs per infested stem (1.80 ± 0.04), the highest proportion of infested stems (0.63 ± 0.01), and the highest proportion of cut stems (0.33 ± 0.01) in 'Hockett'. Seven out of eight cultivars had greater grain weight for infested stems than for uninfested stems. These cultivars may have compensatory responses to larval feeding injury. Overall, these barley cultivars contain varying levels of antixenosis, antibiosis, and differing levels of yield compensation. Our results provide foundational knowledge on barley traits that will provide a framework to further develop C. cinctus resistant or tolerant barley cultivars.

First record of native entomopathogenic nematodes from Montana agroecosystems

A total of 30 different agricultural fields in the Golden Triangle Region of Montana, USA were surveyed, and 150 soil samples were evaluated for the presence of entomopathogenic nematodes (EPNs). The authors isolated EPNs from 10% of the collected samples. The recovered isolates were identified as Steinernema feltiae and Heterorhabditis bacteriophora by using morphological and molecular analysis. Steinernema feltiae was found from two fields, Kalispell (S. feltiae 1) and Choteau (S. feltiae 2). Steinernema feltiae (1 and 2) differed significantly from each other in terms of morphological characters for infective juveniles (distance from anterior end to excretory pore and nerve ring) and 1st generation males (body length, spicule length, gubernaculum length, oesophagus, tail, and anal body diameter). Steinernema feltiae 2 and H. bacteriophora were recovered from the same field in Choteau. All these species were recovered from wheat fields with sandy clay loam and loam soils with 3.3 to 3.4% organic matter content and pH 8.

Mate Choice Behavior of Female Field Crickets Is Not Affected by Exposure to Heterospecific Calling Songs

Many animals produce acoustic signals to mark territories and attract mates. When different species produce acoustic signals simultaneously, the signals create a noisy environment, with potential acoustic interference between species. Theoretical studies suggest that such reproductive interference may have strong effects on species interaction. For example, the inferior resource competitor can survive if its disadvantage is counterbalanced by superiority in reproductive interference. Two field cricket species, Teleogryllus occipitalis (Audinet-Serville) (Orthoptera: Gryllidae) and Loxoblemmus equestris Saussure (Orthoptera: Gryllidae), cooccur in the same habitat. A previous study has shown that L. equestris is an inferior species to T. occipitalis in terms of resource competition. Therefore, we predicted that mate location and choice behavior of female T. occipitalis would be negatively affected by the acoustic signals of L. equestris and tested this with a series of playback experiments. The mate choice behavior of female T. occipitalis was not significantly affected by the calling song of L. equestris. Our results suggest that the acoustic interference does not explain the cooccurrence of the two species in the same habitat.

Spinosad and Mixtures of an Entomopathogenic Fungus and Pyrethrins for Control of Sitona lineatus (Coleoptera: Curculionidae) in Field Peas

The pea leaf weevil, Sitona lineatus L., is an important pest of field peas and faba beans in most temperate regions. As no information is currently available on efficacy of biopesticides for S. lineatus control, laboratory bioassays were performed to evaluate the impact of biopesticides (spinosad, Beauveria bassiana strain GHA, pyrethrins, B. bassiana GHA + pyrethrins, and B. bassiana GHA + azadirachtin) against adults of this pest. The concentrations used in this bioassay were 0.1, 0.5, 1.0, and 2.0 times the lowest labeled application rate of each product. Results were further verified in cage experiments by assessing biopesticide effects on adult mortality and feeding damage in pea plants. The impact of biopesticides on mortality of larvae of two beneficial species, Chrysoperla carnea and Adalia bipunctata, was also tested in laboratory conditions. We found spinosad to be the most promising candidate, causing 100% adult mortality at high and medium concentrations. Beauveria bassiana and its combination with pyrethrins caused 60-62% adult mortality, but only at the highest concentration. In contrast, B. bassiana + azadirachtin and pyrethrins treatments caused only minimal adult mortality at all concentrations. In cage experiments, spinosad and B. bassiana + pyrethrins had significant effects on adult mortality and provided foliage protection from adult feeding. Conversely, the fungus treatment alone showed inconsistent performance. Beauveria bassiana and spinosad were generally harmless to C. carnea and A. bipunctata larvae, but B. bassiana + pyrethrins was toxic toward beneficial species. These results could help to improve integrated pest management programs intended to control S. lineatus.

A Review of Interactions between Insect Biological Control Agents and Semiochemicals

Biological control agents and semiochemicals have become essential parts of the integrated pest management of insect pests over recent years, as the incorporation of semiochemicals with natural enemies and entomopathogenic microbials has gained significance. The potential of insect pheromones to attract natural enemies has mainly been established under laboratory conditions, while semiochemicals from plants have been used to attract and retain natural enemies in field conditions using strategies such as trap crops and the push–pull mechanism. The best-known semiochemicals are those used for parasitoids–insect pest–plant host systems. Semiochemicals can also aid in the successful dispersal of entomopathogenic microbials. The use of semiochemicals to disseminate microbial pathogens is still at the initial stage, especially for bacterial and viral entomopathogens. Future studies should focus on the integration of semiochemicals into management strategies for insects, for which several semiochemical compounds have already been studied. More effective formulations of microbial agents, such as granular formulations of entomopathogenic fungi (EPFs), along with bio-degradable trap materials, could improve this strategy. Furthermore, more studies to evaluate species-specific tactics may be needed, especially where more than one key pest is present.

Implications of using two natural enemies of Tuta absoluta (Lepidoptera: Gelechiidae) toward tomato yield enhancement

Tomato leaf miner (TLM), Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) is one of the most destructive tomato pests worldwide. We tested quantity and quality of tomato fruits after simultaneous use of two biological control agents, the predatory mirid bug Nesidiocoris tenuis (Reuter) and the egg parasitoid Trichogramma brassicae Bezdenko against TLM. We varied the timing of predator releases (before or after pest establishment) and the number of parasitoids released (ten or 30 females per week per m2). The highest number of fruits per cage, percentage of undamaged fruits, total yield weight, and undamaged yield weight were all obtained with predator-in-first treatments, with or without parasitoid releases. Furthermore, measures of fruit quality were also highest in predator-in-first treatments, including, highest percentage of water, greatest proportional fresh weight of carbohydrates, most lycopene, most β-carotene, most flavonoids, and highest total chlorophyll. Thus, our findings support a predator-in-first augmentation approach for management of TLM.

Field efficacy of insect pathogen, botanical, and jasmonic acid for the management of wheat midge Sitodiplosis mosellana and the impact on adult parasitoid Macroglenes penetrans populations in spring wheat

The wheat midge, Sitodiplosis mosellana, is a serious pest of wheat worldwide. In North America, management of S. mosellana in spring wheat relies on the timely application of pesticides, based on midge adults levels caught in pheromone traps or seen via field scouting during wheat heading. In this context, biopesticides can be an effective alternative to pesticides for controlling S. mosellana within an Integrated Pest Management program. A field study using insect pathogenic fungus Beauveria bassiana GHA, nematode Steinernema feltiae with Barricade polymer gel 1%, pyrethrin, combined formulations of B. bassiana GHA and pyrethrin, Jasmonic acid (JA) and chlorpyrifos (chemical check) was performed to determine to which extent they affect midge larval populations, kernel damage levels, grain yield, and quality, and the impacts on adult parasitoid Macroglenes penetrans populations. The results indicated that biopesticides JA and S. feltiae were the most effective in reducing larval populations and kernel damage levels, and produced a higher spring wheat yield when compared to the water control at both study locations (East Valier and North Valier, Montana, USA). Increased test weight in wheat had been recorded with two previous biopesticides at East Valier but not for North Valier, when compared over water control. These results were comparable in efficacy to the chlorpyrifos. This study also suggested that B. bassiana and pyrethrin may work synergistically, as exemplified by lower total larval populations and kernel damage levels when applied together. This study did not demonstrate the effect of any treatments on M. penetrans populations.

Use of Taxonomic and Trait-Based Approaches to Evaluate the Effects of Transgenic Cry1Ac Corn on the Community Characteristics of Soil Collembola

Nontarget soil fauna in fields planted with transgenic Bt crops may be influenced by the Bt protein following crop establishment. Here, we investigated the effects of transgenic Cry1Ac corn Bt-799 on soil Collembola using both taxonomic and trait-based approaches in an experimental field in northeast China from 2014 to 2015. The relationship between the collembolan community and environmental variables (including corn type) was investigated using redundancy analysis (RDA). In May 2015, we found that collembolan species richness, Shannon-Wiener's index, and all trait values examined in transgenic Cry1Ac corn (Event Bt-799, Bt corn) were lower than in its near isoline (Zheng 58, non-Bt corn). However, this significant influence did not persist in the subsequent corn growth period. For all other sampling periods over 2-yr study, all indices based on taxonomic (abundance, species richness, and Shannon-Wiener's index) and trait-based (number of ocelli, body size, pigmentation, furcula development, and antennae length) approaches in Bt corn were not significantly different from non-Bt corn. The results showed no significant difference between the two corn types in the repeated-measures analysis of variance (ANOVA). Moreover, redundancy analysis (RDA) showed that corn type only explained 1% of the variation in the collembolan community. These results suggested that Bt corn did not affect collembolan community characteristics in the short term.

Multidimensional relationships of herbicides with insect-crop food webs

Controlling weeds is critical for improving the yield and quality of crops. Herbicides are the most commonly applied pesticides in agro-ecosystems. Herbicides affect insects directly as contact damage and indirectly by influencing food supplies. The innate susceptibility, life stages, and mode of feeding of insects can affect the herbicide-insect interaction. Interaction of herbicides with insect pest and beneficial insects is mainly indirect and absence of weeds either can reduce the insect population or causes switching of host plant and hence can also increase the population. The direct effect of herbicides depends on carrier or surfactant used. Presence of herbicides also provides surfactant to insecticides and increases impact of insecticides. At present, most reports on impact of herbicides indicate alterations in insect survival or egg production due to increase or decrease in host plant population as an indirect affect, only a handful studies reported a direct topical effect of these herbicides on egg, larvae/nymphs and adults of various insects. Further exploration of this interaction seems intriguing. Use of bio-herbicides, cultural control methods, and judicious use of herbicides could offer ecologically sustainable approaches to reduce impact of herbicides on insects.

Field and Laboratory Studies on the Ecology, Reproduction, and Adult Diapause of the Asian Comma Butterfly, Polygonia c-aureum L. (Lepidoptera: Nymphalidae)

Adult diapause and reproduction of a nymphalid butterfly, Polygonia c-aureum L., were investigated in field and laboratory examinations. Laboratory studies showed that old virgin male butterflies of non-diapausing generations had heavy accessory glands and simplex, which were suppressed in diapausing generations. The number of eupyrene sperm bundles in the duplex increased with adult age, whereas testis size decreased with age. Field examinations indicated that reproductive development of both sexes of diapausing generations in autumn was suppressed, and developed in spring. We attempted to estimate the physiological age of wild-caught males, as adult male age can be estimated from the testis size. We also attempted to determine whether or not wild male butterflies had mated from the development of the accessory glands and simplex, as well as the number of eupyrene sperm bundles in the duplex, by comparing unmated males with mated males. Field examinations suggest that almost all females in a population of non-diapausing generations mated and showed a tendency toward polyandry, while in the diapausing generation, in spring, monoandry rather than polyandry predominated. This suggests a different mating strategy between non-diapausing and diapausing generations.

Effects of photoperiod, temperature and aging on adult diapause termination and post-diapause development in female Asian comma butterflies, Polygonia c-aureum Linnaeus (Lepidoptera: Nymphalidae)

Polygonia c-aureum females exhibit photoperiodically induced imaginal diapause, characterized by cessation of ovarian development. Females grown at a short daylength (SD) entered imaginal diapause, whereas those grown at a long daylength (LD) produced eggs rapidly after adult emergence at 21 °C. The termination of diapause was influenced by daylength: diapause ended faster at LD than SD. Complete termination of diapause took 30 days in unchilled females reared under LD at 21 °C. On the other hand, prompt, synchronized and strong diapause termination occurred at post-chilling periods. Photoperiods at post-chilling periods affected ovarian development, when the length of pre-chilling periods or the length of chilling periods was shorter, suggesting that these treatments were not enough to complete diapause development. Ovarian development proceeded earlier in chilled and subsequent warmed females than unchilled females. Wing damage was remarkable at post-chilling periods when females were reared under an adequate length of pre-chilling and chilling periods, especially comparing with females under pre-overwintering conditions without chilling, indicating that post-diapause reproductive development was weak in unchilled females. Thus, exposure to low temperatures is necessary for a strong diapause termination in this butterfly.

Pheromone-Trap Monitoring System for Pea Leaf Weevil, Sitona lineatus: Effects of Trap Type, Lure Type and Trap Placement within Fields

The pea leaf weevil, Sitona lineatus, is an important pest of field peas and faba beans worldwide. Present sampling techniques that rely on detection of adult feeding damage are labor intensive, time consuming and require repeated sampling. Semiochemical-based pest monitoring systems could improve pea leaf weevil management. This study, which was conducted in the Golden Triangle region of Montana, tested several factors that potentially might affect capture rates of pheromone-baited traps, including trap and lure type and trap placement. Pheromone-baited pitfall and ramp traps caught significantly more adults than ground or delta traps, in all study areas. Pitfall traps baited with gray rubber septa captured significantly more adults than traps baited with membrane formulations or controls in both pea and lentil fields. In addition, pheromone-baited pitfall traps positioned in the southern part of pea fields captured relatively higher numbers of adults than those placed in northern parts of fields, although this difference was not significant. These findings can be used to improve adult weevil monitoring and should be taken into consideration when developing an integrated pest management program.

Effects of Irradiation Dose on Sperm Production, Insemination, and Male Mating Possible Period in the Sweetpotato Weevil (Coleoptera: Brentidae)

The sterile insect technique (SIT) has been used for the control or eradication of target insect pests. To successfully apply SIT, it is very important to clarify the effect of irradiation on male reproduction in the target pest, because their mating and spermiogenesis abilities affect the success of eradication program. The sweetpotato weevil, Cylas formicarius (Fabricius) (Coleoptera: Brentidae) is a notorious and worldwide pest of sweet potato. We investigated the effect of irradiation at five doses ranging from 0 (control) to 150 Gy on 9-d-old males. Survival rate of the control (no treatment) remained high from day 10 to 20 of adult life, whereas higher doses of irradiation reduced it, maximally by approximately 70%. Mating rates showed a similar tendency. Radiation dose neither affected sperm production nor sperm transfer at any dose, although spermiogenesis is active during the adult stage. However, radiation dose affected the lifetime total of ejaculated sperm number, likely because of fewer matings by irradiated males. These results suggest that use of a dose of 150 Gy or higher is appropriate for the final step of eradication of this weevil. At least, lower dose of irradiation may arise the inadequate sterilization, resulting in a failure of eradication program. We conclude that weekly release of sweetpotato weevil sterilized with high dose, achieving complete sterilization, could be useful for eradication program after reducing the population by male annihilation method.

Why Does Not the Leaf Weight-Area Allometry of Bamboos Follow the 3/2-Power Law?

The principle of similarity (Thompson, 1917) states that the weight of an organism follows the 3/2-power law of its surface area and is proportional to its volume on the condition that the density is constant. However, the allometric relationship between leaf weight and leaf area has been reported to greatly deviate from the 3/2-power law, with the irregularity of leaf density largely ignored for explaining this deviation. Here, we choose 11 bamboo species to explore the allometric relationships among leaf area (A), density (ρ), length (L), thickness (T), and weight (W). Because the edge of a bamboo leaf follows a simplified two-parameter Gielis equation, we could show that A ∝ L² and that A ∝ T². This then allowed us to derive the density-thickness allometry ρ ∝ T^b and the weight-area allometry W ∝ A^(b+3)/2 ≈ A^9/8, where b approximates -3/4. Leaf density is strikingly negatively associated with leaf thickness, and it is this inverse relationship that results in the weight-area allometry to deviate from the 3/2-power law. In conclusion, although plants are prone to invest less dry mass and thus produce thinner leaves when the leaf area is sufficient for photosynthesis, such leaf thinning needs to be accompanied with elevated density to ensure structural stability. The findings provide the insights on the evolutionary clue about the biomass investment and output of photosynthetic organs of plants. Because of the importance of leaves, plants could have enhanced the ratio of dry material per unit area of leaf in order to increase the efficiency of photosynthesis, relative the other parts of plants. Although the conclusion is drawn only based on 11 bamboo species, it should also be applicable to the other plants, especially considering previous works on the exponent of the weight-area relationship being less than 3/2 in plants.

Characterization of Resistance to Cephus cinctus (Hymenoptera: Cephidae) in Barley Germplasm

Most barley cultivars have some degree of resistance to the wheat stem sawfly (WSS), Cephus cinctus Norton (Hymenoptera: Cephidae). Damage caused by WSS is currently observed in fields of barley grown in the Northern Great Plains, but the impact of WSS damage among cultivars due to genetic differences within the barley germplasm is not known. Specifically, little is known about the mechanisms underlying WSS resistance in barley. We characterized WSS resistance in a subset of the spring barley CAP (Coordinated Agricultural Project) germplasm panel containing 193 current and historically important breeding lines from six North American breeding programs. Panel lines were grown in WSS infested fields for two consecutive years. Lines were characterized for stem solidness, stem cutting, WSS infestation (antixenosis), larval mortality (antibiosis), and parasitism (indirect plant defense). Variation in resistance to WSS in barley was compared to observations made for solid-stemmed resistant and hollow-stemmed susceptible wheat lines. Results indicate that both antibiosis and antixenosis are involved in the resistance of barley to the WSS, but antibiosis seems to be more prevalent. Almost all of the barley lines had greater larval mortality than the hollow-stemmed wheat lines, and only a few barley lines had mortality as low as that observed in the solid-stemmed wheat line. Since barley lines lack solid stems, it is apparent that barley has a different form of antibiosis. Our results provide information for use of barley in rotation to control the WSS and may provide a basis for identification of new approaches for improving WSS resistance in wheat.

Field efficacy of Bacillus thuringiensis galleriae strain SDS-502 for the management of alfalfa weevil and its impact on Bathyplectes spp. parasitization rate

Alfalfa weevil, Hypera postica Gyllenhal, is an important pest in forage alfalfa worldwide, and especially so on the Northern Plains of North America. Neither the weevil-specific fungus, Erynia phytonomi, nor the weevil's parasitoids are able to routinely suppress outbreaks as they do in the eastern U.S. A new Bacillus thuringiensis var. galleriae, having a Cry8Da coleopteran-active toxin, has been recently commercialized. We examined the efficacy of this B. thuringiensis product against the H. postica in replicated field trials in north central Montana. Because it has been suggested that efficiency of the parasitoids, Bathyplectes curculionis and Oomyzus incertus, was inversely proportional to host numbers (i.e., parasitoid efficiency increased when host population is low), we also sought to determine if a partial reduction of larval H. postica populations with a B. thuringiensis would yield to greater parasitoid efficiency, manifested as higher percent parasitism among the surviving larvae. The B. thuringiensis gave 27-40% reduction in weevil numbers at the low label rate, 55-59% for the high label rate. Mean parasitism at the two research locations varied from 5-26% and 17-36% respectively, but application of the B. thuringiensis had no significant effect on parasitism levels, i.e. parasitism was not greater in treated than in carrier control plots.

Internode morphometrics and allometry of Tonkin Cane Pseudosasa amabilis

Pseudosasa amabilis (McClure) (Poales: Gramineae) is a typical bamboo species naturally distributed in large area of south China and famous for its culm strength. Although bamboos were found to share the same development rule, the detailed internode morphology of bamboo culm was actually not fully expressed. We explored internode morphology of P. amabilis using 11 different physical parameters in different dimensions (1–4). As Taylor's power law (TPL) is generally applicable to describe relationship between mean and variance of population density, here we used TPL to evaluate the differences between internodes, and further, the relationship between dimension and TPL. Results showed that length (L), hollow radius (HR), hollow area (HA), hollow cylinder volume (HCV), total cylinder volume (TCV), density (De), and weight (W) all presented positive skewed distribution in varying degrees. For the basic one‐dimensional parameters, the 9th internode was the longest, the 7th the heaviest, while thickness (T) decreased with internodes. Diameter (D) decreased in general but with an inconspicuous local mode at the 5–6th internodes, potentially due to the rapid height growth. The longest (9th) internode was the “turning point” for T‐D and HR‐D relationships. Scatter plot changing trends of W to the one‐dimensional parameters after the heaviest (7th) internode were reversed, indicating a deceleration of growth speed. TPL was not holding well in one‐dimensional parameters (R²: 0.5413–0.8125), but keep increasing as the parameter's dimension increasing (R² > 0.92 for two‐dimensional, R² > 0.97 for three‐dimensional, and R² > 0.99 for four‐dimensional parameters.), suggesting an emergence mechanism of TPL related to both the physical dimensions of morphological measures and the allometric growth of bamboo. From the physical fundamental level, all existences are the expression of energy distribution in different dimensions, implying a more general rule that energy distribution holds better TPL in higher dimension level.

Role of the aphid species and their feeding locations in parasitization behavior of Aphelinus abdominalis, a parasitoid of the lettuce aphid Nasonovia ribisnigri

Aphid species feeding on lettuce occupy distinct feeding sites: the lettuce aphid Nasonovia ribisnigri prefers to feed on heart leaves, whereas the potato aphid Macrosiphum euphorbiae feeds only on outer leaves. The aphid parasitoid Aphelinus abdominalis, known to be able to regulate M. euphorbiae on many crops, has recently been indicated as a promising biocontrol candidate also for use against N. ribisnigri, a major pest of lettuce. This study therefore examined A. abdominalis parasitization preference between N. ribisnigri and M. euphorbiae and its ability to parasitize aphids feeding on different parts of lettuce plants. In addition, life history traits of A. abdominalis on these aphid species were investigated. In no-choice laboratory experiments on leaf discs and 24 h exposure, A. abdominalis successfully parasitized 54% and 60% of the offered N. ribisnigri and M. euphorbiae, respectively, with no significant difference. In the corresponding choice experiment, however, A. abdominalis had a tendency for a significantly higher preference for M. euphorbiae (38%) compared to N. ribisnigri (30%). Growth chamber experiments on whole plants demonstrated that A. abdominalis was able to parasitize aphids, regardless of their feeding locations on lettuce plants. However, aphid feeding behavior had a significant effect on the parasitization rate. A. abdominalis parasitized significantly higher percentages of M. euphorbiae or N. ribisnigri when aphids were exposed separately to parasitoids on whole lettuce plants as compared with N. ribisnigri exposed only on heart leaf. A significant preference of A. abdominalis for M. euphorbiae compared to N. ribisnigri was also observed in the growth chamber choice experiment. A high percentage of adult emergence (> 84%) and female-biased sex ratio (> 83%) were found irrespective of the aphid species.

Varietal Preferences and Within-Orchard and Tree Distribution of Newly Recorded Gall Midges, Dasineura amaramanjarae and Procontarinia mangiferae (Diptera: Cecidomyiidae), From Commercial Mango Cultivars in Pakistan

Gall midges (Diptera: Cecidomyiidae) damage mango by feeding on flowers and fruit tissues, inducing galls on leaves, and providing inoculums of anthracnose. Dasineura amaramanjarae Grover and Procontarinia mangiferae (Felt), two gall midges that damage flowers in all mango-growing areas of the world, have recently been recorded in Pakistan, and studies were conducted in 2011 and 2012 on the within-tree and orchard distribution patterns and cultivar preference of both species in Pakistan at one location (Rahim Yar Khan). Both gall midge species were found on all mango cultivars examined (Chaunsa, Fajri, Dusehri, Surkha, Sindhri, and Anwar Ratul), with the most damage occurring to Surkha and Dusehri. Research on midge distribution patterns in different parts of mango orchards (central, southern, northern, eastern, and western sides) showed these species to be found in all areas, with the greatest numbers in the central and southern regions. In addition, both species were most abundant on the lower parts of the mango tree canopy.

Effects of pre-overwintering conditions on eupyrene and apyrene spermatogenesis after overwintering in Polygonia c-aureum (Lepidoptera: Nymphalidae)

Sperm polymorphism is widely known in invertebrates. In insects, Lepidoptera has two types of sperm: nucleated eupyrene (fertile) sperm and anucleated apyrene (unfertile) sperm. These sperm types are produced during post-embryogenesis, and eupyrene spermatogenesis precedes apyrene spermatogenesis. During overwintering, spermatogenesis stops and a portion of undifferentiated-stage spermatocytes degenerate. After overwintering, spermatogenesis restarts with unaffected spermatogonia. However, how new spermatozoa arise in the adult testes after overwintering is not known in Lepidoptera. In this study, we investigated the spermatogenesis events in the nymphalid butterfly Polygonia c-aureum after overwintering under various environmental conditions. Our results indicate that both eupyrene and apyrene spermatogenesis restart at any stopping stage and sperm of these types are regenerated in no particular order after adult insect overwintering. This suggests that the spermatogenesis occurring after overwintering proceeds without embryogenetic restrictions related to the developmental sequence.