Potential Use of Trichogramma pintoi as a Biocontrol Agent Against Heortia vitessoides (Lepidoptera: Pyralidae)

A comparative approach for life history and functional response demonstrates similar survival strategies for Trichogramma evanescens and T. pintoi

BACKGROUND

Egg parasitoids are important biological control agents of lepidopteran pests of agricultural crops. Trichogramma evanescens Westwood and T. pintoi Voegele (Hymenoptera: Trichogrammatidae) are egg parasitoids with worldwide importance. The parasitoid selection necessitates comparative assessment of the life table traits and functional response analysis to provide insights into their effectiveness in pest control. In this study, we examined their life table traits including survivorship and reproductivity, and functional response and associated parameters i.e., attack coefficient and handling time.

RESULTS

Life table parameters, using age-stage, two-sex theory, revealed similar survival and reproductive strategies for both species. For example, the female longevity, oviposition days and fecundity did not differ between both species. Exceptionally, the male longevity of T. evanescens was shorter than that of T. pintoi. The population growth parameters such as gross reproductive rate (GRR), net reproductive rate (R0), intrinsic rate of increase (r), finite rate of increase (λ), and mean generation time (T) did not differ between species. The polynomial logistic regression yielded a type III functional response and a non-linear least square analysis revealed different attack coefficient and similar handling time. However, their parasitism rate differed between the lowest (five eggs) and highest (80 eggs) initial host egg densities such that T. evanescens had a lower parasitism rate at the lowest density and higher parasitism rate at the highest density.

CONCLUSION

The similarity in survival strategies and minor differences in host handling of both parasitoids are discussed in terms of relevance to applied biological control applications and evolutionary traits. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Functional and Numerical Responses of Trichogramma euproctidis (Hymenoptera: Trichogrammatidae) to Helicoverpa armigera (Lepidoptera: Noctuidae) Under Laboratory Conditions

The tomato fruitworm Helicoverpa armigera (Hübner) is regarded as a serious pest that affects a great number of field crops globally. One of the environmentally safe alternatives to the utilization of insecticides is controlling H. armigera via the release of biological control agents by employing parasitoids, e.g., trichogrammatid species. One of the desired parasitoids indigenous to southwestern Iran is Trichogramma euproctidis (Girault). To anticipate the outcomes of augmentative releases of T. euproctidis in the field, the numerical and functional responses of female T. euproctidis that parasitizes the eggs of H. armigera were determined in the laboratory. The densities of host eggs per glass tube arena (length: 10 cm, diameter: 1 cm) were 2, 4, 8, 16, 32, 64, or 128 individuals. The functional response to the eggs of H. armigera indicated Holling's type II response. The estimated handling time and attack rate from the random parasitoid equation were 0.6898 h and 0.00823 h, respectively. This indicates that, at the maximum level, each T. euproctidis was capable of parasitizing 34.79 eggs a day. At the 128 host egg density, the number of eggs laid, that is, the numerical response, ascended as the density of host eggs increased up to a maximum of 89.90 eggs per female. According to the obtained results of the present investigation, T. euproctidis can serve as an appropriate candidate for augmentative biological control of H. armigera. Nevertheless, it is necessary to conduct complementary experiments in greenhouses and open fields.

Repeated mechanical damage enhanced Aquilaria sinensis resistance to Heortia vitessoides through jasmonic acid

Introduction

The leaf-chewing pest Heortia vitessoides severely threatens the growth and development of Aquilaria sinensis. In our previous study, we found that mechanical damage (MD) to stem enhanced A. sinensis sapling resistance to H. vitessoides larvae.

Methods

To reveal the defense mechanisms underlying this observation, we analyzed the types and contents of volatile organic compounds (VOCs), phytohormone contents, and expression of phytohormone-related genes in response to MD and herbivory wounding(HW).

Results

Here, we identified several VOCs, such as the pesticides fenobucarb and 2,4-di-tert-butylphenol, in mature leaf (ML) of MD-treated plants. Compared with salicylic acid (SA) or the ethylene (ET) pathway, jasmonic acid (JA) content and JA-related genes were more strongly upregulated. Interestingly, we found a dramatic difference between JA-related upstream and downstream genes expression in YL and ML, which confirmed that JA-Ile accumulation in MD-ML and HW-ML could be derived from local damaged site.

Discussion

Taken together, we provide evidence that the JA pathway plays a dominant role in the A. sinensis response to MD and HW.

Lethal, transmission, behavioral, and physiological effects of Metarhizium anisopliae against gregarious larvae of Heortia vitessoides and synergistic effects between Metarhizium anisopliae and insecticides

BACKGROUND

Heortia vitessoides Moore is a severe pest of Aquilaria sinensis (Lour.) Gilg, an important source of agarwood. In recent years, large amounts of chemical insecticides have been applied in A. sinensis plantations to deal with the outbreak of H. vitessoides, causing residue problems that reduce the quality and price of agarwood. Herein, we hypothesize that the widely applied biocontrol agent, Metarhizium anisopliae (Metschn.) Sorokin, can effectively kill the gregarious larvae of H. vitessoides through direct contact and horizontal transmission.

RESULTS

At the concentration of 1 × 10⁹ conidia/mL, the three M. anisopliae strains caused 100% mortality of H. vitessoides larvae. In addition, mixing donor larvae (previously treated with M. anisopliae conidia) with receptor larvae (which did not directly contact M. anisopliae conidia) caused significantly higher mortality of receptor larvae than the control receptors. This is due to the horizontal transmission of M. anisopliae conidia among live larvae, which was proven by pictures taken by scanning electron microscopy and induced activities of immunity-related enzymes of donor and receptor larvae. Behavioral bioassays showed that M. anisopliae conidia had little effect on the aggregation tendency of H. vitessoides larvae but may trigger feeding-avoidance behavior depending on M. anisopliae strains and concentrations. Interestingly, joint use of sublethal concentrations of M. anisopliae and chemical insecticides significantly increased larval mortality than each agent alone, indicating synergistic effects between M. anisopliae and insecticide against H. vitessoides.

CONCLUSION

This study may provide a new strategy to suppress H. vitessoides population and reduce the use of chemical insecticides. © 2023 Society of Chemical Industry.

Biotic and abiotic factors that affect parasitism in Trichogramma pintoi (Hymenoptera: Trichogrammatidae) as a biocontrol agent against Heortia vitessoides (Lepidoptera: Pyralidae)

The parasitoid wasp, Trichogramma pintoi, is a promising candidate for inundative release against Heortia vitessoides. Parasitoid females can regulate the sex of their offspring in response to environmental and biological factors. In pest control programs utilizing these parasitoids, male overproduction is not conducive to success. To optimize the production of T. pintoi as an egg parasitoid of H. vitessoides, factors affecting the rates of parasitism and eclosion and the percentage of females among T. pintoi offspring, such as temperature, photoperiod, host age, host density, maternal age, maternal density, and food, were investigated. The proportion of T. pintoi female offspring was significantly affected by temperature, photoperiod, host density, maternal age, and maternal density. The female offspring percentage decreased in response to host density (160 eggs), maternal age (≥ 4 days old), maternal density (≥ 4 females), photoperiods (24:0 and 18:6 L:D), and extremely low temperature (15 °C). However, host age and female diet did not affect the proportion of female offspring. According to the present work, female parasitoid production can be maximized under laboratory conditions of 25 °C, 75% relative humidity, and a photoperiod of 0:24 h (L:D) via exposure of forty 1-day-old H. vitessoides eggs for 24 h or eighty 1-day-old H. vitessoides eggs to a newly emerged, mated female fed a 10% sucrose solution until the female dies. These findings will guide mass production efforts for this parasitoid.

Genome Assembly and Comparative Analysis of the Egg Parasitoid Wasp Trichogramma dendrolimi Shed Light on the Composition and Evolution of Olfactory Receptors and Venoms

Trichogramma dendrolimi is one of the most successfully industrialized Trichogramma species used to control agricultural and forestry pests in China. However, the molecular mechanisms underlying its host recognition and parasitism remain largely unknown, partially due to the limited genome information of this parasitoid wasp. Here, we present a high-quality de novo assembly of T. dendrolimi through a combination of Illumina and PacBio sequencing technologies. The final assembly had a length of 215.2 Mb and contains 316 scaffolds with a scaffold N50 size of 1.41 Mb. Repetitive sequences with a length of 63.4 Mb and 12,785 protein-coding genes were identified. Significantly expanded gene families were identified to be involved in the development and regulatory processes, while remarkably contracted gene families were involved in the transport processes in T. dendrolimi. The olfactory and venom-associated genes were identified in T. dendrolimi and 24 other hymenopteran species, using uniform methods combining BLAST and HMM profiling. The identified venom genes of T. dendrolimi were enriched in antioxidant activity, tricarboxylic acid cycle, response to oxidative stress and cell redox homeostasis. Our study provides an important resource for comparative genomics and functional studies to interpret the molecular mechanisms underlying host recognition and parasitism of Trichogramma species.

Cloning and characterization of a novel DNase gene from Trichogramma pretiosum

DNase is a powerful tool for a series of molecular biology applications. Developing a strategy for large-scale production of DNase with high purity and activity is critical for scientific research. In this study, a previously uncharacterized gene with nuclease activity was found in Trichogramma pretiosum genome. Pichia pastoris GS115 was preferred as the host to overcome the issues related to prokaryotic expression. Under the optimal conditions, the activity of T. pretiosum DNase (Tp-DNase) reached 1940 U/mL of culture supernatant in fed-batch fermentation. Using ion-exchange chromatography and adsorption chromatography, Tp-DNase was produced with a purity of >99% and molecular weight of 45 kDa. In vitro DNA degradation experiments showed that Tp-DNase could effectively degrade dsDNA, and its activity was slightly higher than that of bovine pancreas DNase I under the same conditions. Moreover, Tp-DNase can be used to eliminate nucleic acid contamination and improve the accuracy of nucleic acid detection.

Additive interactions of some reduced-risk biocides and two entomopathogenic nematodes suggest implications for integrated control of Spodoptera litura (Lepidoptera: Noctuidae)

Higher volumes of conventional and novel chemical insecticides are applied by farmers to control resistant strains of armyworm (Spodoperta litura) in Pakistan without knowing their risks to the environment and to public health. Ten reduced-risk insecticides were tested for their compatibility with two entomopathogenic nematodes (EPNs); Heterorhabditis indica and Steinernema carpocapsae against S. litura. The insecticide emamectin benzoate was highly toxic (LC₅₀ = 2.97 mg/l) against 3^rd instar S. litura larvae when applied alone whereas, novaluron and methoxyfenozide were the least toxic (LC₅₀ = 29.56 mg/l and 21.06 mg/l), respectively. All the insecticides proved harmless against the two EPNs even 96 h after treatment. Indoxacarb, flubendiamide and spinetoram produced the greatest mortalities (72–76%) of S. litura larvae after 72 h when applied in mixtures with H. indica. Lowest mortalities (44.00 ± 3.74% and 48.00 ± 2.89) were observed for mixtures of H. indica with methoxyfenozide and chlorfenapyr, respectively. The positive control treatments with both EPNs (S. carpocapsae and H. indica) produced > 50% mortality 96 h after treatment. For insecticide mixtures with S. carpocapsae, only indoxacarb produced 90% mortality of larvae, whereas, indoxacarb, flubendiamide, emamectin benzoate, and spinetoram produced 90–92% mortality of larvae when applied in mixtures with H. indica. Additive interactions (Chi-square < 3.84) of EPN mixtures with reduced volumes of reduced-risk insecticides suggest opportunities to develop more environmentally favorable pest management programs for S. litura.