The control of risk hypothesis: reactive vs. proactive antipredator responses and stress-mediated vs. food-mediated costs of response

Inducible defences against predators evolve because they reduce the rate of direct predation, but this benefit is offset by the cost (if any) of defence. If antipredator responses carry costs, the effect of predators on their prey is partitioned into two components, direct killing and risk effects. There is considerable uncertainty about the strength of risk effects, the factors that affect their strength, and the mechanisms that underlie them. In some cases, antipredator responses are associated with a glucocorticoid stress response, and in other cases they are associated with trade-offs between food and safety, but there is no general theory to explain this variation. Here, I develop the control of risk (COR) hypothesis, predicting that proactive responses to predictable and controllable aspects of risk will generally have food-mediated costs, while reactive responses to unpredictable or uncontrollable aspects of predation risk will generally have stress-mediated costs. The hypothesis is grounded in laboratory studies of neuroendocrine stressors and field studies of food-safety trade-offs. Strong tests of the COR hypothesis will require more studies of responses to natural variation in predation risk and the physiological consequences of these responses, but its explanatory power can be illustrated with existing case studies.

Use of an innovative T-tube maze assay and the proboscis extension response assay to assess sublethal effects of GM products and pesticides on learning capacity of the honey bee Apis mellifera L

Transgenic Cry1Ac+CpTI cotton (CCRI41) is a promising cotton cultivar throughout China but side effects and especially sublethal effects of this transgenic cultivar on beneficial insects remain poorly studied. More specifically potential sublethal effects on behavioural traits of the honey bee Apis mellifera L. have not been formally assessed despite the importance of honey bees for pollination. The goal of our study was to assess potential effects of CCRI41 cotton pollen on visual and olfactory learning by honey bees. After a 7-day oral chronic exposure to honey mixed with either CCRI41 pollen, imidacloprid-treated conventional pollen (used as positive sublethal control) or conventional pollen (control), learning performance was evaluated by the classical proboscis extension reflex (PER) procedure as well as a T-tube maze test. The latter assay was designed as a new device to assess potential side effects of pesticides on visual associative learning of honey bees. These two procedures were complementary because the former focused on olfactory learning while the latter was involved in visual learning based on visual orientation ability. Oral exposure to CCRI41 pollen did not affect learning capacities of honey bees in both the T-tube maze and PER tests. However, exposure to imidacloprid resulted in reduced visual learning capacities in T-tube maze evaluation and decreased olfactory learning performances measured with PER. The implications of these results are discussed in terms of risks of transgenic CCRI41 cotton crops for honey bees.

Artificial night lighting inhibits feeding in moths

One major, yet poorly studied, change in the environment is nocturnal light pollution, which strongly alters habitats of nocturnally active species. Artificial night lighting is often considered as driving force behind rapid moth population declines in severely illuminated countries. To understand these declines, the question remains whether artificial light causes only increased mortality or also sublethal effects. We show that moths subjected to artificial night lighting spend less time feeding than moths in darkness, with the shortest time under light conditions rich in short wavelength radiation. These findings provide evidence for sublethal effects contributing to moth population declines. Because effects are strong under various types of light compared with dark conditions, the potential of spectral alterations as a conservation tool may be overestimated. Therefore, restoration and maintenance of darkness in illuminated areas is essential for reversing declines of moth populations.

Lethal and sublethal effects of chlorantraniliprole on Spodoptera cosmioides (Lepidoptera: Noctuidae)

BACKGROUND

The Spodoptera cosmioides (Walker, 1858) population has increased in Bacillus thuringiensis Berliner (Bt) soybean crops in Argentina. As there are no registered products for its control, the recommended insecticides for S. frugiperda are used. The aim of this study was therefore to determine the lethal concentration (LC) of chlorantraniliprole and its sublethal effects on the biological and reproductive functions of S. cosmioides, an emerging soybean pest in Argentina.

RESULTS

An ingestion toxicity bioassay showed that chlorantraniliprole was active against larvae of the second instar, and after 48 h of exposure LC₅₀ was 0.054 µg mL^-1 H₂ O. In the study of sublethal effect, chlorantraniliprole induced changes in the life cycle of exposed S. cosmioides, which required more time to complete all stages of development (larval, pupal and adult stages). Pupal weight was also higher in larvae exposed to sublethal concentrations of chlorantraniliprole. Adult fecundity was decreased: the number of eggs laid by each adult female moth, as compared with control females, was two (LC₁₅ ) and eight (LC₃₀ ) times lower.

CONCLUSION

These results indicate that chlorantraniliprole has toxicity against S. cosmioides larvae. Sublethal effects on the biological and reproductive performance of this species can help optimize integrated pest management programs. © 2018 Society of Chemical Industry.

Toxicity and Sublethal Effects of Flupyradifurone, a Novel Butenolide Insecticide, on the Development and Fecundity of Aphis gossypii (Hemiptera: Aphididae)

The cosmopolitan pest Aphis gossypii (Glover) causes considerable economic losses on various crops by its feeding damage and transmitting diseases around the world. Flupyradifurone is a novel butenolide pesticide; its toxicity on A. gossypii parent generation (F0) was estimated following treatment with LC25 concentration for 48 h. The adult longevity and fecundity of the F0 individuals treated by flupyradifurone showed no significant decrease in comparison with the control. Life table method was used to evaluate the sublethal effects on progeny population (F1). Results showed that the development time of the fourth instar and the preadult as well as the total pre-reproductive period were significantly prolonged, while their fecundity was significantly decreased compared with the control. Additionally, the intrinsic rate of increase (r), the finite rate of increase (λ), and the net reproductive rate (R0) of F1 were all significantly lower in the group treated by LC25 than in the control group. These results reveal that the sublethal concentration of flupyradifurone could suppress the population growth of A. gossypii and indicate that this novel insecticide may be as a useful tool in pest management.

Dissecting the roles of FTZ-F1 in larval molting and pupation, and the sublethal effects of methoxyfenozide on Helicoverpa armigera

BACKGROUND

In holometabolous insects, the major developmental transitions - larval molting and pupation - are triggered by a pulse of 20-hydroxyecdysone (20E) and coordinated by juvenile hormone. Methoxyfenozide (MF), an ecdysteroid agonist, represents a new class of insect growth regulators and is effective against lepidopteran pests. Fushi-tarazu factor 1 (FTZ-F1) is an ecdysone-inducible transcription factor. To date, the effect of MF on 20E-response genes remains unclear, and we speculate the involvement of FTZ-F1 in MF's growth regulating effect.

RESULTS

MF at LC₂₅ and LC₁₀ caused severe ecdysis failure in Helicoverpa armigera, extended their larval duration, lowered their pupal weight, and reduced the respiratory, pupation and emergence rates. Furthermore, sublethal doses of MF inhibited ecdysteroidogenesis and lowered the intrinsic 20E titer, but showed an inductive effect on 20E-response genes including HaFTZ-F1. HaFTZ-F1, predominantly expressed in larval epidermis, was markedly upregulated before or right after larval ecdysis, and maintained a high level in prepupal stage. Knockdown of HaFTZ-F1 in 4th-instar larvae severely impaired larval ecdysis, whereas its knockdown in final-instar larvae caused abnormal pupation. Moreover, knocking down HaFTZ-F1 downregulated three critical ecdysteroidogenesis genes, lowered 20E titer, and suppressed the expression of 20E receptors and 20E-response genes. The introduction of 20E into HaFTZ-F1-RNAi larvae partly relieved the negative effects on the 20E-induced signaling cascade.

CONCLUSION

Our findings reveal the adverse effects of sublethal doses of MF on the development of H. armigera and elucidate the resulting perturbations on the 20E-induced signaling cascade; we propose that HaFTZ-F1 regulates ecdysis and pupation by mediating 20E titer and its signaling pathway. © 2020 Society of Chemical Industry.

Sublethal Effects of Cyantraniliprole and Imidacloprid on Feeding Behavior and Life Table Parameters of Myzus persicae (Hemiptera: Aphididae)

The green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae), is an agricultural pest that seriously infests many crops worldwide. This study used electrical penetration graphs (EPGs) and life table parameters to estimate the sublethal effects of cyantraniliprole and imidacloprid on the feeding behavior and hormesis of M. persicae The sublethal concentrations (LC30) of cyantraniliprole and imidacloprid against adult M. persicae were 4.933 and 0.541 mg L(-1), respectively. The feeding data obtained from EPG analysis indicated that the count probes and number of short probes (<3 min) were significantly increased when aphids were exposed to LC30 of imidacloprid-treated plants. In addition, the phloem-feeding behavior of M persicae was significantly impaired on fed tobacco plants treated with cyantraniliprole and imidacloprid at LC30 Analysis of life table parameters indicated that the growth and reproduction of F1 generation aphids were significantly affected when initial adults were exposed to LC30 of cyantraniliprole and imidacloprid. The nymphal period, female longevity, total preoviposition period, and mean generation time were significantly prolonged when initial adults were exposed to LC30 of imidacloprid. By comparison, these parameters were prolonged but not significantly in the cyantraniliprole treatment. The fecundity and gross reproductive rate were significantly increased in the treated groups. Similarly, the net reproductive rate was greater in the treated group than the control group. Our results indicate that treatment with LC30 of imidacloprid and cyantraniliprole would lead to a hormetic response of M. persicae, with higher likelihood of occurrence when initial adults were exposed to LC30 of cyantraniliprole.

Ultrasound-Induced Escherichia coli O157:H7 Cell Death Exhibits Physical Disruption and Biochemical Apoptosis

Ultrasound has attracted great interest of both industry and scientific communities for its potential use as a physical processing and preservation tool. In this study, Escherichia coli O157:H7 was selected as the model microbe to investigate the ultrasound-induced cell death. Slight variations in membrane potential and ion exchanges across membrane induced by low-intensity ultrasound increased the membrane permeability of E. coli O157:H7, and this reversible sublethal effect can preserve the viability of E. coli O157:H7 and meanwhile be beneficial for bioprocessing application. In comparison, high-intensity ultrasound resulted in irreversible lethal effect on E. coli O157:H7, which can be applied in the field of microbial inactivation. In addition, both low- and high-intensity ultrasound induced either physical destruction or trigger genetically encoded apoptosis of E. coli O157:H7. Accumulation of reactive oxygen species and decrease of adenosine tri-phosphate might be related to the physiological and biochemical hallmarks of apoptosis, including exposed phosphatidylserine and activated caspases in E. coli O157:H7. The result provides novel insight into the mechanisms of non-thermal physical treatment on the inactivation of bacteria and lays foundation for the further research on the cell signaling and metabolic pathway in apoptotic bacteria.

Lethal and Sublethal Effects of Essential Oils From Artemisia khorassanica and Vitex pseudo-negundo Against Plodia interpunctella (Lepidoptera: Pyralidae)

Plodia interpunctella (Hübner, 1813) is a polyphagous and key pest of different stored products worldwide. The lethal and sublethal effects of essential oils of Artemisia khorassanica Podl. and Vitex pseudo-negundo (Hausskn) were studied on P. interpunctella The chemical constituents of the essential oils were also assessed using gas chromatography-mass spectrometry. Assays showed that the fumigant toxicity of A. khorassanica (LC₅₀: 9.60 µl/liter air) was higher than V. pseudo-negundo (LC₅₀: 23.05 µl/liter air). Moreover, the speed of mortality caused by A. khorassanica oil (LT₅₀: 2.07 h) was higher than V. pseudo-negundo (LT₅₀: 3.11 h). To assess the sublethal effects of the essential oils, adult moths were exposed to the LC₃₀ of each essential oil, and life table parameters and energy contents of the surviving P. interpunctella were studied. Exposure to sublethal concentration of A. khorassanica negatively affected the life table of P. interpunctella, and also the protein, lipid, and glycogen contents of the larvae that came from treated adults. Vitex pseudo-negundo also affected lipid, protein, and glycogen contents of P. interpunctella The intrinsic rate of increase (r_m), finite rate of increase ([Formula: see text]), and doubling time (DT) were not significantly different between control and V. pseudo-negundo treatment. According with these results, both tested essential oils, especially one extracted from A. khorassanica, have potential applications for the integrated management of P. interpunctella.

Modification of Flight and Locomotion Performances, Respiratory Metabolism, and Transcriptome Expression in the Lady Beetle Harmonia axyridis through Sublethal Pesticide Exposure

Biological control is usually used in combination with chemical control for practical agricultural applications. Thus, the influence of insecticides on the natural predators used for biological control should be investigated for integrated pest management. The ladybird Harmonia axyridis is an effective predator on aphids and coccids. Beta-cypermethrin is a broad-spectrum insecticide used worldwide for controlling insect pests. H. axyridis is becoming increasingly threatened by this insecticide. Here, we investigated the effect of a sublethal dose of beta-cypermethrin on flight, locomotion, respiration, and detoxification system of H. axyridis. After exposure to beta-cypermethrin, succinic female adults flew more times, longer distances, and during longer time periods. Exposure to a sublethal dose of beta-cypermethrin also promoted an increase in walking rate, walking distance, walking duration, and also an increase in respiratory quotient and respiratory rate. To investigate the effects of beta-cypermethrin on H. axyridis detoxification system, we analyzed the transcriptome of H. axyridis adults, focusing on genes related to detoxification systems. De novo assembly generated 65,509 unigenes with a mean length of 799 bp. From these genes, 26,020 unigenes (40.91% of all unigenes) exhibited clear homology to known genes in the NCBI non-redundant database. In addition, 10,402 unigenes were annotated in the Cluster of Orthologous Groups database, 12,088 unigenes were assigned to the Gene Ontology database and 12,269 unigenes were in the Kyoto Encyclopedia of Genes and Genome (KEGG) database. Exposure to beta-cypermethrin had significant effects on the transcriptome profile of H. axyridis adult. Based on uniquely mapped reads, 3,296 unigenes were differentially expressed, 868 unigenes were up-regulated and 2,248 unigenes were down-regulated. We identified differentially-expressed unigenes related to general detoxification systems in H. axyridis. This assembled, annotated transcriptome provides a valuable genomic resource for further understanding the molecular basis of detoxification mechanisms in H. axyridis.

Role of Toxicokinetic and Toxicodynamic Parameters in Explaining the Sensitivity of Zebrafish Larvae to Four Metals

Given the persistence and toxic potencies of metal contaminants in ecosystems, animals, and human beings, they are considered to be hazardous global pollutants. While the lethality of metal toxicities (e.g., LC₅₀) can significantly vary, even within the same species, the underlying mechanisms are less well-understood. In this study, we developed a subcellular two-compartment toxicokinetic-toxicodynamic (TK-TD) model for zebrafish larvae when exposed to four metals (cadmium, lead, copper, and zinc) to reveal whether differences in metal toxicity (LC₅₀ values) were dominated by the TK or TD processes. Results showed that the subcellular TK and TD parameters of the four metals were significantly different, and the bioconcentration factor (BCF) value of copper was higher than those of the other metals. We also found that the TD parameter internal threshold concentration (C_IT) was significantly positively correlated to the LC₅₀ values (R² = 0.7), suggesting a dominant role of TD processes in metal toxicity. Furthermore, the combined parameter C_IT/BCF for a metal-sensitive fraction (BCF_MSF), which linked exposure to effects through the TK-TD approach, explained up to 89% of the variation in toxicity to the four metals. The present study suggests that the observed variation in toxicity of these four metals was mainly determined by TD processes but that TK processes should not be ignored, especially for copper.

Alternative control of Aedes aegypti resistant to pyrethroids: lethal and sublethal effects of monoterpene bioinsecticides

BACKGROUND

The mosquito Aedes aegypti is intensively controlled because it is a vector of viruses that cause numerous diseases, especially in tropical regions. As a consequence of the indiscriminate use of insecticides, populations from different regions have become resistant to pyrethroids. Here, we analyzed the lethal and sublethal effects of essential oil of Aristolochia trilobata and its major compounds on A. aegypti from susceptible and pyrethroid-resistant populations.

RESULTS

Our results showed that the toxicity of the different compounds and behavioral changes in response to them are dependent on the stage of the insect life cycle. The monoterpene ρ-cymene caused high mortality in both larvae and adult females of A. aegypti, including those from the pyrethroid-resistant population. The monoterpenes limonene and linalool caused a sublethal effect in the larvae, triggering changes in the swimming pattern.

CONCLUSION

This study highlights the potential of the essential oil of A. trilobata and its major compounds ρ-cymene and limonene for the control of A. aegypti and reveals the importance of analyzing sublethal effects on the population dynamics of the A. aegypti mosquito. © 2017 Society of Chemical Industry.

Sublethal Effects of Beauveria bassiana (Ascomycota: Hypocreales) on Life Table Parameters of Frankliniella occidentalis (Thysanoptera: Thripidae)

We assessed effects of parental exposure to Beauveria bassiana on life history traits of subsequent generations of western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae). Progeny from individuals that survived fungal exposure as second instars had significantly shorter egg stages, but longer prepupal development times than corresponding untreated controls. However, survivorship to adulthood of these progeny groups did not differ. Although fecundities of the parental types did not differ, the sex ratio of progeny from fungal-treated parents was male-biased, whereas sex ratio of progeny from untreated control parents was even. We calculated life table parameters for the progeny and found that all parameters, except for generation time, were significantly less for the progeny of fungal-treated parents than for progeny of untreated parents. The intrinsic rate of increase, finite rate of increase, net reproductive rate, mean generation time, and gross reproductive rate were 0.199 d(-1), 1.229 d(-1), 21.84, 15.48 d, and 27.273, respectively, for progeny of treated thrips, and 0.266 d(-1), 1.316 d(-1), 52.540, 14.92 d, and 70.64, respectively, for progeny of control thrips. Consequently, population projections demonstrated that offspring of parents exposed to B. bassiana would increase their population more slowly than those from untreated parents. These results demonstrate that B. bassiana has sublethal effects that reduce the reproductive success of F. occidentalis and these effects should be taken into account when evaluating its use in management programs for F. occidentalis.

Lethal and sublethal effects of fluralaner on the two-spotted spider mites, Tetranychus urticae Koch (Acari: Tetranychidae)

BACKGROUND

Two-spotted spider mite (TSSM), Tetranychus urticae Koch is a serious agricultural pest and has developed high levels of resistance to many acaricides. Hence, screening new acaricides is important in the control of TSSM. Fluralaner, a novel isoxazoline, has high activity against agricultural and ectoparasitic pests; however, little information is available about its effects on agricultural mites. Lethal and sublethal effects of fluralaner towards TSSM eggs and female adults were therefore evaluated in this study.

RESULTS

Fluralaner exhibited higher activity towards TSSM female adults (LC₅₀ , 0.49 mg L^-1 ) compared with commercial acaricides including fenpyroximate, pyridaben and hexythiazox, and also excellent activity towards eggs (LC₅₀ , 0.36 mg L^-1 ). The results of a sublethal effect study showed a significant reduction in the duration and fecundity of female adults with increases in the tested concentrations. The net reproductive rate (R₀ ) decreased to 67.34 ± 3.96 and 50.29 ± 3.40 offspring per individual in LC₁₀ and LC₃₀ treatments compared with control (108.31 ± 7.61 offspring per individual). The intrinsic rate of increase (r) and finite rate of increase (λ) in the controls (0.30 and 1.36 d^-1 ) were significantly higher than in the LC₃₀ treatment (0.25 and 1.29 d^-1 ); whereas, they were almost identical to values for the LC₁₀ treatment. No change in mean generation time (T) was observed at sublethal concentrations treatments.

CONCLUSION

Our results demonstrated that fluralaner has high acaricidal activity and could be considered a potential acaricide for TSSM management. © 2019 Society of Chemical Industry.

Sublethal Concentration of Beta-Cypermethrin Influences Fecundity and Mating Behavior of Carposina sasakii (Lepidoptera: Carposinidae) Adults

The purpose of this study was to evaluate the sublethal effects of the beta-cypermethrin on calling behavior and fecundity of a major fruit-boring pest of apple, Carposina sasakii Matsumura. The mating rate, fertility (total number of eggs laid per female), and adult longevity of adults were remarkably decreased as compared with that in control when the adults were exposed to 10% lethal concentrations (LC10) of beta-cypermethrin (LC10♀ × LC10♂), and the age-specific survival rate (lx) was also negatively affected by sublethal beta-cypermethrin especially for the LC10♀× LC10♂ mating combination. However, the age-specific fecundity (mx) was stimulated particularly in the combination of CK♀× LC10♂. Furthermore, the oviposition period was prolonged and the number of eggs was significantly increased for combinations of CK♀× LC10♂ and LC10♀× CK♂. In the mating experiments, males in control or LC10-beta-cypermethrin treatments preferred to mate with females in control. It might be because of lower calling rate of female survivors treated with sublethal beta-cypermethrin. Our data indicate that treatment of beta-cypermethrin had a sublethal effect on the development and production of C. sasakii, and their mating behavior changes in surviving adults that may contribute to assortative mating.

Lethal and Sublethal Effects of Clothianidin on the Development and Reproduction of Bemisia tabaci (Hemiptera: Aleyrodidae) MED and MEAM1

The Bemisia tabaci (Gennadius) cryptic species complex includes important crop pests, and among them, the cryptic species Mediterranean (MED) and Middle East-Asia Minor 1 (MEAM1) cause substantial crop losses in China. The second-generation neonicotinoid clothianidin acts as an agonist of the nicotinic acetylcholine receptor in the insect nervous system and has both stomach and contact activity. In this study, the toxicity of clothianidin and five other insecticides to MED and MEAM1 was examined. The sublethal effects of clothianidin on the development and reproduction of MED and MEAM1 were also investigated. Among the six insecticides tested, clothianidin showed toxicities to both MED and MEAM1 adults with LC50 values of 5.23 and 5.18 mg/liter, respectively. The sublethal effects of clothianidin were assessed by treating MED and MEAM1 adults with the LC25 of 1.58 and 1.13 mg/liter, respectively. The LC25 treatments accelerated the development of the F1 generation but reduced survival and fecundity of both species. Our results indicate that clothianidin could be useful for the management of B. tabaci MED and MEAM1.

Survival and arm abscission are linked to regional heterothermy in an intertidal sea star

Body temperature is a more pertinent variable to physiological stress than ambient air temperature. Modeling and empirical studies on the impacts of climate change on ectotherms usually assume that body temperature within organisms is uniform. However, many ectotherms show significant within-body temperature heterogeneity. The relationship between regional heterothermy and the response of ectotherms to sublethal and lethal conditions remains underexplored. We quantified within-body thermal heterogeneity in an intertidal sea star (Pisaster ochraceus) during aerial exposure at low tide to examine the lethal and sublethal effects of temperatures of different body regions. In manipulative experiments, we measured the temperature of the arms and central disc, as well as survival and arm abscission under extreme aerial conditions. Survival was related strongly to central disc temperature. Arms were generally warmer than the central disc in individuals that survived aerial heating, but we found the reverse in those that died. When the central disc reached sublethal temperatures of 31-35°C, arms reached temperatures of 33-39°C, inducing arm abscission. The absolute temperature of individual arms was a poor predictor of arm abscission, but the arms lost were consistently the hottest at the within-individual scale. Therefore, the vital region of this sea star may remain below the lethal threshold under extreme conditions, possibly through water movement from the arms to the central disc and/or evaporative cooling, but at the cost of increased risk of arm abscission. Initiation of arm abscission seems to reflect a whole-organism response while death occurs as a result of stress acting directly on central disc tissues.

Evaluation of Sublethal Effects of Sulfoxaflor on the Green Peach Aphid (Hemiptera: Aphididae) Using Life Table Parameters

The green peach aphid, Myzus persicae (Sulzer), is an important insect pest of many crops around the world. Pesticide-induced hormesis may be an alternative mechanism for pest resurgence. In this study, life table parameters were applied to the estimation of sulfoxaflor-induced hormesis of adult M. persicae following 2-d LC25 concentration exposure. Leaf-dip bioassays showed that the sulfoxaflor possessed high toxicity against M. persicae, with an LC50 of 0.059 mg/liter. The results indicated that the exposure of the parent generation of M. persicae to sublethal sulfoxaflor induced increase in reproduction and prolongation of immature development duration in the first progeny generation. Both R0 and GRR of aphids for treatment group were significantly higher than for the control in F1 generation, and the mean generation time was significantly postponed in treated group. These results suggest a hormesis induced by lower concentration of sulfoxaflor in M. persicae. It would be useful for assessing the overall effects of sulfoxaflor on M. persicae.

Novel meta-diamide insecticide, broflanilide, suppresses the population of common cutworm Spodoptera litura through its lethal and sublethal effects

BACKGROUND

Broflanilide has been registered in China for the control of Lepidoptera and Coleoptera pests, and is widely used to control the target pests at lethal and sublethal levels. The lethal and sublethal effects of broflanilide on the common cutworm (CCW) Spodoptera litura Fabricius, a representative Lepidopteran pest in agricultural crops, were examined to explore its ecological influence on pests.

RESULTS

In F₀ , broflanilide had little influence on the hatchability of eggs, but significantly reduced the neonate survival rate. The lethal activity of broflanilide towards third-instar larvae and adults was 0.13 mg kg^-1 (LD₅₀ ) and 3.59 mg L^-1 (LC₅₀ ) respectively at 48 h. After being treated with a sublethal dose (LD₁₀ and LD₃₀ ) of broflanilide, the duration of third- to sixth-instar larvae and the mean fecundity of reproductive females were significantly increased, but pupation rate, weight of pupae and life-cycle rate were significantly decreased. In F₁ , the duration of F₁ larvae and the doubling time were prolonged, whereas the rates of pupation and the life cycle were decreased by 14.92% and 18.00%, respectively. The intrinsic rate of increase, finite rate of increase and net reproductive rate in the sublethal group were lower than in the control group. The relative fitness of F₁ treated by LD₁₀ and LD₃₀ was 0.81 and 0.66, respectively.

CONSLUSION

Broflanilide not only has highly lethal activity, but also suppresses the population growth and progeny of CCW, as a critical factor for guidelines of its usage in the field.

Sublethal Effects of Triflumezopyrim on Biological Traits and Detoxification Enzyme Activities in the Small Brown Planthopper Laodelphax striatellus (Hemiptera: Delphacidae)

The small brown planthopper [Laodelphax striatellus (Fallén) (Hemiptera, Delphacidae)] is one of the most destructive insect pests of rice and has developed strong resistance to several kinds of chemical insecticides. Triflumezopyrim, a novel mesoionic insecticide developed by Corteva Agriscience (formerly DuPont Crop Protection), has efficient biological activity in controlling sucking insects, such as the planthopper. However, the effects of triflumezopyrim on the growth and reproduction of L. striatellus have not been reported. In this study, an F₅ generation was obtained by conducting five rounds of insecticide screening on a sensitive L. striatellus strain (F₀ generation). An age-stage life table procedure was used to evaluate the effects of a sublethal concentration (LC₅₀) of triflumezopyrim on the biological parameters of L. striatellus. Compared with those of the F₀ generation, the intrinsic rate of increase (r), the finite rate (λ), and the net reproductive rate (R₀) of the F₅ generation were significantly decreased; nevertheless, the average duration of life (T) was not significantly affected. The results of detoxification enzyme activity assays indicated that the glutathione S-transferase and cytochrome P450 monooxygenase (P450) activities in the F₅ generation were significantly higher than those in the F₀ generation. The contents of vitellogenin (Vg) and vitellogenin receptor (VgR) were also detected, and the results indicated that the contents of Vg and VgR in the F₅ generation were significantly decreased compared to those in the F₀ generation. Furthermore, we detected the relative expression of ecdysone receptor (EcR), Vg, and VgR in the F₀ and F₅ generations and found that the relative expression levels of Vg and VgR in the F₅ generation female adults were obviously lower than those in the F₀ generation (P < 0.05), whereas the relative expression of EcR was slightly increased, although the difference was not significant (P > 0.05). Based on these results, a sublethal concentration (median lethal concentration, LC₅₀) of triflumezopyrim may inhibit the generational growth and reproduction of L. striatellus. Moreover, our results may provide a reference for further studies of the suitability and resistance mechanisms of L. striatellus subjected to a sublethal dose of triflumezopyrim.

A Neonicotinoid Affects the Mating Behavior of Spalangia endius (Hymenoptera: Pteromalidae), a Biological Control Agent of Filth Flies

Spalangia endius Walker is a parasitoid wasp that is commercially available as a biological control agent for filth fly pests in livestock-rearing operations. Imidacloprid is often used to control these flies. The present study examined the sublethal effect of field-realistic concentrations of imidacloprid on mating behavior, offspring sex ratios, and male preference for virgin females. After exposure to imidacloprid, S. endius females that survived were less likely to mate than control females, which will result in male-biased sex ratios because only mated females can produce daughters. Males did not avoid exposed females, but exposed females were almost always unreceptive. Males that survived exposure to imidacloprid exhibited reduced mating competitiveness against unexposed males. However, if an exposed male mated, his mate's sex ratio and ability to control flies was unaffected. Exposed males were also still able to discriminate against mated, and thus usually unreceptive, females. Together with previous studies, these results suggest that not only does imidacloprid reduce the ability of S. endius females to survive and parasitize hosts, but when an exposed female does survive and parasitize hosts, she is likely to produce just sons, because of her lack of receptivity. More-male-biased populations of S. endius will decrease their efficacy for fly control. Thus, the use of imidacloprid along with this parasitoid may be financially inefficient for pest management.

Potential Toxicity of α-Cypermethrin-Treated Nets on Tuta absoluta (Lepidoptera: Gelechiidae)

Insect-proof nets are thought to be effective physical barriers to protect tomato crops against several insect pests, including the invasive tomato pest, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae). However, protected tomato crops are frequently infested by this destructive pest, and there is a higher infestation of plants closer to openings in Mediterranean greenhouses, suggesting that immigrating adults can easily walk on these protective materials and find a way to reach the crop. Laboratory bioassays were carried out to characterize the potential toxicity of α-cypermethrin-treated insect-proof nets (Agronet) against T. absoluta adults. The data showed that the net acts mainly through a variety of chronic sublethal effects rather than acute ones. Reduced longevity and, more markedly, a reduced number of laid eggs were observed after the moths were exposed to the treated net over the duration of their lifetimes. A Y-tube experiment showed that the treated net does not affect the T. absoluta olfaction cues for host location. In contrast, when the moths were given the option to choose either the treated or the untreated net in laboratory cages, they significantly preferred the untreated one. The toxicological significance and the functional implications of these subtle effects for the implementation of integrated T. absoluta management strategies are discussed.

Are Mummies and Adults of Eretmocerus mundus (Hymenoptera: Aphelinidae) Compatible With Modern Insecticides?

The parasitic wasp Eretmocerus mundus (Mercet) is an important natural enemy of the widespread key pest Bemisia tabaci (Gennadius). The toxicity of 11 modern insecticides applied at their maximum field recommended rate in Spain was tested in two life stages of E. mundus: adults and mummies. Laboratory and persistence tests were conducted and effects assessed not only in terms of mortality but on reproductive performance as well. Some insecticides caused the same effect to both life stages: flubendiamide, methoxyfenozide, spiromesifen, and flonicamid were harmless, while spinosad and sulfoxaflor were harmful. The last two insecticides cannot be used jointly with E. mundus under any condition because they were highly persistent. The rest of tested insecticides (spirotetramat, metaflumizone, deltamethrin, abamectin, and emamectin) caused some direct mortality to one or both life stages and/or affected reproduction of the parasitic wasp and their harmful effect in the field ranged from short lived (metaflumizone and spirotetramat) to slightly persistent (emamectin) and to moderately persistent (abamectin and deltamethrin). Therefore, they could be recommended for use in integrated pest management programs together with the natural enemy if appropriate safety intervals after insecticide application are observed.

20E and MAPK signal pathway involved in the effect of reproduction caused by cyantraniliprole in Bactrocera dorsalis Hendel (Diptera: Tephritidae)

BACKGROUND

It is a common phenomenon that insecticides affect insect reproduction and insect hormones. After cyantraniliprole treatment, the egg production and remating behavior of female Bactrocera dorsalis were affected, a phenomenon of 'hormesis' appeared, but the change at the molecular level was unknown. Therefore, we investigated the fertility, insect hormone titers and transcription levels and used RNAi to prove the function of genes, to explore the molecular mechanism of cyantraniliprole causing reproductive changes in female B. dorsalis.

RESULTS

LC₂₀ treatment promoted egg production, while LC₅₀ treatment inhibited it. Both high and low concentrations inhibited female ovaries' development and reduced the length of the ovarian tubes. Among insect hormones, only the titer of 20-hydroxyecdysone (20E) changed significantly. According to the KEGG pathway enrichment analysis of RNA-seq, there are significant differences in insect hormone synthesis and MAPK signal pathways between treatments. Furthermore, 20E biosynthetic genes, BdVgs and BdVgR were all down-regulated, and multiple MAPK signaling pathway genes were up-regulated. Based on qRT-PCR, the expression of BdCyp307A1, BdCyp302A1, BdMEKK4 and BdMAP2K6 within 1-11 days after treatment were consistent with the change of 20E titer. The BdVg1 and BdVg2 in LC₅₀ were still suppressed, while the LC₂₀ returned to normal in 9-11 days. RNAi indicated that BdMEKK4 and BdMAP2K6 participated in the transcriptional regulation of BdCyp307A1 and BdCyp302A1, then affected the levels of BdVgs.

CONCLUSION

Cyantraniliprole affected 20E through MAPK signal pathway, causing many genes to be down-regulated during the early period but up-regulated during the late period, ultimately affecting the reproduction of B. dorsalis. © 2021 Society of Chemical Industry.

Cycloxaprid: a novel cis-nitromethylene neonicotinoid insecticide to control Bemisia tabaci

BACKGROUND

Bemisia tabaci is a worldwide insect pest with high ability to develop resistance to many insecticides. Cycloxaprid is a novel cis-configuration neonicotinoid insecticide that is effective against a wide range of imidacloprid-resistant pests.

RESULTS

The lethal and sublethal effects of cycloxaprid on B. tabaci B were estimated. Cycloxaprid showed higher toxicity against adult, nymph and egg of B. tabaci B than imidacloprid. And cycloxaprid provided better efficacies against B. tabaci than imidacloprid in fields. Moreover, cycloxaprid was similarly toxic to the relatively susceptible and imidacloprid-resistant populations. The LC₅₀ of cycloxaprid against the resistant adult, nymph and egg were 6.2, 11.5 and 111.3 mg L^-1 , respectively, while they were 5.7, 8.9 and 129.4 mg L^-1 for the susceptible population. In addition, when resistant adult of B. tabaci B was treated with LC₃₀ of cycloxaprid (3.2 mg L^-1 ), the net reproductive rate and female ratio of F1 generation B. tabaci were reduced. Moreover, the age-specific fecundity demonstrated the highest fecundity sharply decreased in cycloxaprid (7.0 offspring/ day) treated group compared with the control (26.0 offspring/ day).

CONCLUSIONS

Our results indicated that cycloxaprid is a promising insecticide for the management of B. tabaci and insecticide-induced resurgence might not occur after exposure of B. tabaci to low sublethal concentrations of cycloxaprid. © 2019 Society of Chemical Industry.