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

Understanding crop colonization of oilseed rape crops by the cabbage stem flea beetle (Psylliodes chrysocephala L. (Coleoptera: Chrysomelidae))

BACKGROUND

Development of accurate pest monitoring systems is essential for the establishment of integrated pest management strategies. Information about the pest behavior during the colonization process, as well as the sex and reproductive status of the colonizing population often are lacking and hinder their development. The cabbage stem flea beetle (CSFB, Psylliodes chrysocephala) can cause the complete destruction of oilseed rape crops (OSR, Brassica napus). In the present study, the colonization process of OSR fields by the CSFB was studied.

RESULTS

More individuals were caught on the outward facing side of the traps than the side of the trap facing towards the crop at the field border and catches were higher on the trapping units at the center of the field than at its border, suggesting that more beetles were entering than leaving the crop. Catches were higher on lower traps placed near to the crop than on those positioned further from the ground and also were higher during the day than late afternoon and night. The sex-ratio of individuals caught was skewed towards males and sexual maturity was acquired for females during the experiment. Integration of sampling data with local meteorological data showed that the catches correlated mostly with air temperature and relative humidity.

CONCLUSION

This study provides new information about the dispersion of the CSFB in OSR fields during the colonization process, and highlights correlations between local meteorological factors and activity of the CSFB, and represent a new step towards implementing monitoring strategies against this pest. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Frankliniella occidentalis pathogenic fungus Lecanicillium interacts with internal microbes and produces sublethal effects

Frankliniella occidentalis (Thysanoptera: Thripidae) is a pest that feeds on various crops worldwide. A prior study identified Lecanicillium attenuatum and L. cauligalbarum as pathogens of F. occidentalis. Unfortunately, the potential of these two entomopathogenic fungi for the biocontrol of F. occidentalis has not been effectively evaluated. The internal microbes (endosymbionts and the gut microbiota) of insects, especially gut bacteria, are crucial in regulating the interactions between the host and intestinal pathogens. The role of thrips internal microbes in the infection of these two entomopathogenic fungi is also unknown. Therefore, biological control of thrips is immediately needed, and to accomplish that, an improved understanding of the internal microbes of thrips against Lecanicillium infection is essential. The virulence of the two pathogenic fungi against F. occidentalis increased with the conidia concentration. Overall, the LC50 of L. cauligalbarum was lower than that of L. attenuatum, and the pathogenicity degree was adult > pupa > nymphs. The activities of protective enzymes include superoxide dismutase (SOD), catalase (CAT), peroxidase (POD); detoxification enzymes include polyphenol oxidase (PPO), glutathione s-transferase (GSTs), and carboxylesterase (CarE); hormones include ecdysone and juvenile hormone; and the composition and proportion of microorganisms (fungi and bacteria) in F. occidentalis infected by L. cauligalbarum and L. attenuatum have changed significantly. According to the network correlation results, there was a considerable correlation among the internal microbes (including bacteria and fungi), enzyme activities, and hormones, which indicates that in addition to bacteria, internal fungi of F. occidentalis are also involved in the L. cauligalbarum and L. attenuatum infection process. In addition, the development time of the surviving F. occidentalis exposed to L. cauligalbarum or L. attenuatum was significantly shorter than that of the control group. Furthermore, the intrinsic rate of increase (rm), finite rate of increase (λ), net reproductive rate (R0), mean generation time (T), and gross reproductive rate (GRR) were significantly lower in the treatment groups than in the control group. L. attenuatum and L. cauligalbarum have biocontrol potential against F. occidentalis. In addition to bacteria, internal fungi of F. occidentalis are also involved in the infection process of insect pathogenic fungi. Disruption of the internal microbial balance results in discernible sublethal effects. Such prevention and control potential should not be ignored. These findings provide an improved understanding of physiological responses in thrips with altered immunity against entomopathogenic fungal infections, which can guide us toward the development of novel biocontrol strategies against thrips.

Evaluation of a guardian plant system to suppress Frankliniella occidentalis (Thysanoptera: Thripidae) in greenhouse ornamentals

BACKGROUND

Western flower thrips (WFT), Franklinella occidentalis (Pergande), is an economically damaging pest of greenhouse ornamentals. A 'guardian plant system' (GPS) that targeted WFT was evaluated under controlled and commercial greenhouse conditions. This system used mycotized millet grains with the entomopathogenic fungus Beauveria bassiana (Balsamo-Crivelli) Vuillemin applied to soil of potted marigolds, Tagetes patula (L.), combined with the foliar-dwelling predatory mite Neoseiulus (=Amblyseius) cucumeris (Oudemans) in slow-release sachets under controlled greenhouse conditions, and with the addition of a pheromone lure under commercial settings.

RESULTS

Significantly fewer WFT and less foliar damage on GPS was observed over the 10 and 12 weeks experimental periods compared to the untreated controls. Predatory mites were maintained up to 10 weeks with one release under controlled greenhouse conditions and 12 weeks with two releases in commercial greenhouses. In commercial greenhouses, greater numbers of WFT were found on marigolds than on crop plants within 1 m of the system. Fungal granules persisted for 12 weeks up to 2.5 × 105  CFU g-1 in the GPS soil.

CONCLUSION

The use of biological control agents to suppress WFT within a GPS could be a useful IPM strategy for greenhouse production. The marigold GPS attracted WFT which were suppressed primarily through predation by foliar-dwelling predatory mites and to a lesser extent, infection from conidia produced by the granular fungal formulation in the soil. Further investigations into system deployment and fungal granular application rates and new fungal formulations are suggested to improve system efficacy. © 2023 Society of Chemical Industry.

Sublethal effects of emamectin benzoate on development, reproduction, and vitellogenin and vitellogenin receptor gene expression in Thrips hawaiiensis (Thysanoptera: Thripidae)

Thrips hawaiiensis (Morgan) (Thysanoptera: Thripidae) is a sap-sucking pest that seriously damages several crops and reduces their economic value. Exposure to low concentrations of insecticides may have a sublethal effect on surviving insects. In order to provide a reference for the rational application of emamectin benzoate, its sublethal effects on the development and reproduction of T. hawaiiensis were evaluated. Pupal development time was significantly shorter in T. hawaiiensis treated with sublethal concentrations of emamectin benzoate (LC10 and LC20) than in control. Female adult longevity and female total longevity were significantly longer following LC20 treatment than in the control and LC10 treatment groups. Nevertheless, male adult longevity and male total longevity were significantly shorter in the LC10 treatment group than in the control and LC20 treatment groups. The sublethal concentration of emamectin benzoate (LC20) significantly shortened the preadult stages and the mean generation. Meanwhile, it significantly increased the finite rate of increase, intrinsic rate of increase, and net reproductive rate. The fecundity was significantly higher after LC20 treatment than after LC10 and control treatments. Compared with the control group, the LC10 and LC20 groups of T. hawaiiensis adults showed a significantly higher expression of the vitellogenin (Vg) and vitellogenin receptor (VgR) genes, which played a key role in increasing their fecundity. These findings suggest that short-term exposure to sublethal concentrations of emamectin benzoate may lead to a resurgence and secondary outbreak of T. hawaiiensis infestation. The results have practical applications for the management of this important and noxious pest.

Sublethal Effects of Beauveria bassiana Strain BEdy1 on the Development and Reproduction of the White-Backed Planthopper, Sogatella furcifera (Horváth) (Hemiptera: Delphacidae)

Rice (Oryza sativa) is the most important food crop all over the world, while white-backed planthopper (WBPH), Sogatella furcifera (Horváth) (Hemiptera: Delphacidae) is an important pest causing rice yield reduction. The purpose of this study is to evaluate the sublethal effects of strain BEdy1 Beauveria bassiana (Bals.-Criv.) Vuill. (Hypocreales: Cordycipitaceae) on S. furcifera using the two-sex life table analytical method, compare the life tables of the F0 and F1 generations of WBPHs which were treated with sublethal concentrations (LC10, LC25) of B. bassiana BEdy1 with a control group. The results showed that the duration of the egg, 4th-instar and 5th-instar nymph, pre-adult, total pre-oviposition (TPOP) and mean generation time (T) for the LC25 treatment were significantly longer than those of the control and LC10 treatment. However, the duration of the adult, the longevity of male and female adults and the oviposition days of female adults for the LC25 treatment were significantly shortened. The fecundity of female adults, intrinsic rate of increase (r), net reproductive rate (R0) and finite rate of increase (λ) for the LC25 treatment were significantly decreased compared with those of other treatments. The duration of the egg and pre-adult stage for the LC10 treatment were longer than those of the control group, but the population parameters showed no significant difference. Therefore, the LC25 of B. bassiana BEdy1 can inhibit the population growth of S. furcifera.

The effects of the E3 ubiquitin-protein ligase UBR7 of Frankliniella occidentalis on the ability of insects to acquire and transmit TSWV

The interactions between plant viruses and insect vectors are very complex. In recent years, RNA sequencing data have been used to elucidate critical genes of Tomato spotted wilt ortho-tospovirus (TSWV) and Frankliniella occidentalis (F. occidentalis). However, very little is known about the essential genes involved in thrips acquisition and transmission of TSWV. Based on transcriptome data of F. occidentalis infected with TSWV, we verified the complete sequence of the E3 ubiquitin-protein ligase UBR7 gene (UBR7), which is closely related to virus transmission. Additionally, we found that UBR7 belongs to the E3 ubiquitin-protein ligase family that is highly expressed in adulthood in F. occidentalis. UBR7 could interfere with virus replication and thus affect the transmission efficiency of F. occidentalis. With low URB7 expression, TSWV transmission efficiency decreased, while TSWV acquisition efficiency was unaffected. Moreover, the direct interaction between UBR7 and the nucleocapsid (N) protein of TSWV was investigated through surface plasmon resonance and GST pull-down. In conclusion, we found that UBR7 is a crucial protein for TSWV transmission by F. occidentalis, as it directly interacts with TSWV N. This study provides a new direction for developing green pesticides targeting E3 ubiquitin to control TSWV and F. occidentalis.

HMG-Like DSP1 Mediates Immune Responses of the Western Flower Thrips (Frankliniella occidentalis) Against Beauveria bassiana, a Fungal Pathogen

Western flower thrips, Frankliella occidentalis, is a serious pest by directly infesting host crops. It can also give indirect damage to host crops by transmitting a plant virus called tomato spotted wilt virus. A fungal pathogen, Beauveria bassiana, can infect thrips. It has been used as a biopesticide. However, little is known on the defense of thrips against this fungal pathogen. This study assessed the defense of thrips against the fungal infection with respect to immunity by analyzing immune-associated genes of F. occidentalis in both larvae and adults. Immunity-associated genes of western flower thrips were selected from three immunity steps: nonself recognition, mediation, and immune responses. For the pathogen recognition step, dorsal switch protein 1 (DSP1) was chosen. For the immune mediation step, phospholipase A₂ (PLA₂) and prostaglandin E₂ synthase were also selected. For the step of immune responses, two phenoloxidases (PO) genes and four proPO-activating peptidase genes involved in melanization against pathogens were chosen. Dual oxidase gene involved in the production of reactive oxygen species and four antimicrobial peptide genes for executing humoral immune responses were selected. All immunity-associated genes were inducible to the fungal infection. Their expression levels were induced higher in adults than in larvae by the fungal infections. However, inhibitor treatments specific to DSP1 or PLA₂ significantly suppressed the inducible expression of these immune-associated genes, leading to significant enhancement of fungal pathogenicity. These results suggest that immunity is essential for thrips to defend against B. bassiana, in which DSP1 and eicosanoids play a crucial role in eliciting immune responses.

Biological responses of Tetranychus urticae (Acari: Tetranychidae) to sub-lethal concentrations of the entomopathogenic fungus Beauveria bassiana

Tetranychus urticae (Acari: Tetranychidae) is one of the most important pests of agricultural crops with worldwide distribution causing considerable damage to different products. Application of chemical acaricides is one of the most important strategies used for the control of this pest. Entomopathogenic fungi, however, have been proposed as alternative control agents. In this study, sub-lethal effects (LC10 = 6.76 × 102, LC20 = 8.74 × 103, and LC30 = 55.38 × 103 conidia ml-1) of Beauveria bassiana strain TV on the life table parameters of T. urticae were evaluated under laboratory conditions. The results demonstrated that by increasing the concentration, a significant decline was observed in adult longevity of both male and female individuals. Total fecundity of T. urticae was calculated as 45.16, 36.28, 23.98, and 18.21 eggs in control, LC10, LC20, and LC30 treatments, respectively. Sub-lethal concentrations drastically affected the population parameters of this mite pest. The intrinsic rate of increase (r) ranged from 0.1983 to 0.1688 day-1 for the mites treated with distilled water and LC20 treatments, respectively. The net reproductive rate (R0) was affected by the sub-lethal concentrations (lower value at LC30 concentration: 11.19 offspring/individual). Considering the detrimental effects of B. bassiana on some biological parameters of T. urticae, it can be concluded that this product can be used to develop targeted interventions aimed at integrated pest management of this pest.

Fast Recognition of Lecanicillium spp., and Its Virulence Against Frankliniella occidentalis

BACKGROUND

Frankliniella occidentalis (Thysanoptera: Thripidae) is a highly rasping-sucking pest of numerous crops. The entomogenous fungi of Lecanicillium spp. are important pathogens of insect pests, and some species have been developed as commercial biopesticides. To explore Lecanicillium spp. resources in the development of more effective F. occidentalis controls, efficient barcode combinations for strain identification were screened from internal transcribed spacers (ITS), SSU, LSU, TEF, RPB1, and RPB2 genes.

RESULTS

Six genes were used to reconstruct Lecanicillium genus phylogeny. The results showed that ITS, TEF, RPB1, and RPB2 could be used to identify the strains. All phylogenetic trees reconstructed by free combination of these four genes exhibited almost the same topology. Bioassay studies of a purified conidial suspension further confirmed the infection of second-instar nymphs and adult female F. occidentalis by seven Lecanicillium strains. L. attenuatum strain GZUIFR-lun1405 was the most virulent, killing approximately 91.67% F. occidentalis adults and 76.67% nymphs after a 7-day exposure. L. attenuatum strain GZUIFR-lun1405 and L. cauligalbarum strain GZUIFR-ZHJ01 were selected to compare the fungal effects on the number of eggs laid by F. occidentalis. The number of F. occidentalis nymphs significantly decreased when F. occidentalis adults were treated with L. cauligalbarum strain GZUIFR-ZHJ01.

CONCLUSIONS

The combination of ITS and RPB1 could be used for fast recognition of Lecanicillium spp. This is the first report of the pathogenicity of L. attenuatum, L. cauligalbarum, L araneogenum, and L. aphanocladii against F. occidentalis. Additionally, L. cauligalbarum strain GZUIFR-ZHJ01 caused high F. occidentalis mortality and inhibited the fecundity of the pest.

Tomato spotted wilt orthotospovirus influences the reproduction of its insect vector, western flower thrips, Frankliniella occidentalis, to facilitate transmission

BACKGROUND

Tomato spotted wilt orthotospovirus (TSWV), one of the most devastating viruses of ornamental plants and vegetable crops worldwide, is transmitted by the western flower thrips, Frankliniella occidentalis (Pergande), in a persistent-propagative manner. How TSWV influences the reproduction of its vector to enhance transmission and whether infection with TSWV changes the mating behavior of F. occidentalis are not fully understood.

RESULTS

TSWV-exposed thrips had a significantly longer developmental time than non-exposed individuals. More importantly, increased developmental time was predominantly associated with adults, a stage critical for dispersal and virus transmission. In addition, TSWV-exposed F. occidentalis produced substantially more progeny than did non-exposed thrips. Interestingly, most of the increase in progeny came from an increase in males, a sex with a greater dispersal and virus transmission capability. Specifically, the female/male ratio of progeny shifted from 1.3-7.0/1 to 0.6-1.1/1. As for mating behavior, copulation time was significantly longer in TSWV-exposed thrips. Finally, females tended to re-mate less when exposed to the virus. Resistance to re-mating may lead to reduced sperm availability in females, which translates to a larger number of male progeny under a haplodiploid system.

CONCLUSION

These combined results suggest that TSWV can influence the developmental time, mating behavior, fecundity, and offspring sex allocation of its vector F. occidentalis to facilitate virus transmission. As such, a monitoring program capable of the earlier detection of the virus in host plants and/or its insect vector, thrips, using double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA), real time quantitative polymerase chain reaction (RT-qPCR) or virus detection strips might be beneficial for long-term, sustainable management. © 2020 Society of Chemical Industry.

Thermoregulatory response of Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) to infection by Beauveria bassiana, and its effect on survivorship and reproductive success

Behavioral thermoregulation is a defensive strategy employed by some insects to counter infections by parasites and pathogens. Most reported examples of this type of thermoregulatory response involve behavioral fevering. However depending upon the life history of a host-insect and that of the parasite or pathogen, the host may respond by cold-seeking behavior. Thermoregulation is not only ecologically important; it may affect the success of parasites and pathogens as biological control agents. We examined if Frankliniella occidentalis (Pergande) thermoregulates in response to infection by Beauveria bassiana, a fungal pathogen commonly used for biological control. Fungal-infected thrips preferentially moved to cooler areas (~12 °C) while healthy thrips sought out warmer temperatures (~24 °C). This cold-seeking behavior suppressed the growth of B. bassiana in infected thrips, and significantly improved survivorship of infected thrips. At 24 °C, males only survived up to 10 d after infection and females up to 20 d after infection, which was substantially poorer survivorship than that of corresponding healthy individuals. However, individuals of both sexes survived up to 48 d after infection at 12 °C, which was a much less severe reduction in survivorship compared with the effect of B. bassiana infection at 24 °C. The proportion of females among progeny from infected thrips at 12 °C was higher than at 24 °C. Therefore, cold-seeking behavior is beneficial to F. occidentalis when infected by B. bassiana, and its effects should be considered in the use of B. bassiana in biological control programs.

Laboratory and Greenhouse Evaluation of a Granular Formulation of Beauveria bassiana for Control of Western Flower Thrips, Frankliniella occidentalis

Western flower thrips (WFT) is one of the most important pests of horticultural crops worldwide because it can damage many different crops and transmit various plant viruses. Given these significant impacts on plant production, novel methodologies are required to maximize regulation of WFT to minimize crop losses. One particular approach is to develop control strategies for the non-feeding, soil-dwelling stages of WFT. Control of these stages could be enhanced through the use of granules impregnated with entomopathogenic fungi mixed in the soil. The use of soil-applied fungi contrasts with existing approaches in which entomopathogenic fungi are formulated as oil-based suspensions or water-based wettable powders for foliar applications against the feeding stages of WFT. To examine the efficacy of this approach, we evaluated the effects of a granular formulation of Beauveria bassiana on the soil-dwelling, pupal phases of Frankliniella occidentalis in laboratory bioassays and greenhouse experiments. Based on micromorphological observations of fungal conidia during the infection process after treatment of WFT with a B. bassiana suspension, fungal conidia complete the process of surface attachment, germination, and penetration of the body wall of the WFT pupa and enter the host within 60 h of treatment. Given these results, we undertook a controlled greenhouse experiment and applied B. bassiana granules to soil used to cultivate eggplants. Populations of F. occidentalis on eggplants grown in treated soil were 70% lower than those on plants grown in the untreated soil after 8 weeks. Furthermore, when measuring the survival and growth of B. bassiana on granules under different soil moisture conditions, survival was greatest when the soil moisture content was kept at 20%. These results indicate that the application of B. bassiana-impregnated granules could prove to be an effective biological control strategy for use against F. occidentalis under greenhouse conditions.

Pathogenicity of Metarhizium anisopliae and Beauveria bassiana fungi to Tetranychus ludeni (Acari: Tetranychidae)

ABSTRACT The use of acaricides is the main control method for Tetranychus ludeni (Acari: Tetranychidae) in horticultural crops. This mite has been recorded causing damage to sweet potato (Ipomoea batatas L.). The use of pathogenic fungi is an alternative to chemical control. The objective was to evaluate the pathogenicity of the fungi Metarhizium anisopliae (Meetch) Sorok, and Beauveria bassiana (Bals.) Vuill. to phytophagous mite T. ludeni in sweet potato plants. Conidial suspensions of M. anisopliae and B. bassiana, at concentrations of 106 and 107 con.mL-1 were applied to sweet potato leaves. After 24 hours, five females of T. ludeni newly emerged were released on the leaves. The bioassay was arranged in a completely randomized design with factorial arrangement 2 × 2 (two species of fungi and two concentrations) plus the control (distilled water), with 10 repetitions per treatment. The evaluation consisted of observing of three biological parameters of the mite: mortality, oviposition, and repellency, after 24, 48, 72, and 96 hours of contact with the fungi. The isolates of M. anisopliae cause high mortality rates of T. ludeni in laboratory. Beauveria bassiana has the potential to suppress future generations of mite, reducing its oviposition rate. Repellency behavior was not observed.

Sub-lethal concentrations of the entomopathogenic fungus, Beauveria bassiana increase fitness costs of Helicoverpa armigera (Lepidoptera: Noctuidae) offspring

We assessed the effects of exposure of the cotton bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) larvae to the entomopathogenic fungus Beauveria bassiana (isolate DC2) on life history parameters of the subsequent generation. Mortality assays against second instar larvae showed B. bassiana isolates to be significantly virulent, causing high mortality. Life history parameters such as developmental time, fecundity and survivorship were affected in the offspring of survivors of exposure to LC₂₅ and LC₅₀ concentrations of B. bassiana DC2. Pre-adult duration of H. armigera was significantly extended and total longevity and female progeny fecundity were decreased. Oviposition duration was shortened compared to offspring of untreated controls. All population parameters including intrinsic (r) and finite (λ) rates of increase and net (R₀) and gross (GRR) reproductive rates were significantly decreased in offspring derived from H. armigera larvae treated with B. bassiana DC2. The intrinsic rate of increase (r) was 0.198 d^-1, 0.120 d^-1 and 0.111 d^-1, respectively, for the F1 generation of controls (untreated), LC₂₅- and LC₅₀-treated cotton bollworm. The morphogenetic effects of B. bassiana observed due to the indirect effect of sub-lethal concentrations included abnormal pupae and adults and mortality resulted from the malformations. Pupal weight was reduced in offspring of treated individuals but sex ratios did not differ. Our results revealed that B. bassiana increased fitness costs of H. armigera in both direct (mortality) and indirect (disruption of normal development) ways. Adverse effects of sub-lethal fungal treatments on the parent generation carried over to the next generation.

Population Projection and Development of the Mythimna loreyi (Lepidoptera: Noctuidae) as Affected by Temperature: Application of an Age-Stage, Two-Sex Life Table

The Mythimna (=Leucania) loreyi (Duponchel) has recently emerged as a major pest of grain crops in China. Little is known about its basic biology and ecology, making it difficult to predict its population dynamics. An age-stage, two-sex life table was constructed for this insect when reared on maize in the laboratory at five constant temperatures (18, 21, 24, 27, and 30 °C). Both the intrinsic rate of increase (r) and finite rate increase (λ) increased as temperature significantly increased and mean generation time (T) decreased significantly with increasing temperature. The highest values for net reproductive rate (R0) and fecundity were observed at 24 °C. However, M. loreyi was able to develop, survive, and lay eggs at all temperatures tested (18-30 °C). Development rates at different temperatures for the egg, larval, pupal, as well as for a total preoviposition period, fit a linear equation. The lower threshold temperatures of egg, larval, pupal, preoviposition, and total preoviposition period were 8.83, 10.95, 11.67, 9.30, and 9.65 °C, respectively. And their effective accumulated temperatures were 87.64, 298.51, 208.33, 66.47, and 729.93 degree-days, respectively. This study provides insight into the temperature-based phenology and population ecology in M. loreyi. The results will benefit population dynamics monitoring, prediction, and management of this insect pest in the field.

Integrated pest management in western flower thrips: past, present and future

Western flower thrips (WFT) is one of the most economically important pest insects of many crops worldwide. Recent EU legislation has caused a dramatic shift in pest management strategies, pushing for tactics that are less reliable on chemicals. The development of alternative strategies is therefore an issue of increasing urgency. This paper reviews the main control tactics in integrated pest management (IPM) of WFT, with the focus on biological control and host plant resistance as areas of major progress. Knowledge gaps are identified and innovative approaches emphasised, highlighting the advances in 'omics' technologies. Successful programmes are most likely generated when preventive and therapeutic strategies with mutually beneficial, cost-effective and environmentally sound foundations are incorporated. © 2017 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Lack of resistance development in Bemisia tabaci to Isaria fumosorosea after multiple generations of selection

The emergence of insecticide resistant insect pests is of significant concern worldwide. The whitefly, Bemisia tabaci, is an important agricultural pest and has shown incredible resilience developing resistance to a number of chemical pesticides. Entomopathogenic fungi such as Isaria fumosorosea offer an attractive alternative to chemical pesticides for insect control, and this fungus has been shown to be an effective pathogen of B. tabaci. Little is known concerning the potential for the development of resistance to I. fumosorosea by B. tabaci. Five generations of successive survivors of B. tabaci infected by I. fumosorosea were assayed with I. fumosorosea. No significant differences in susceptibility to I. fumosorosea, number of ovarioles, or ovipostioning were seen between any of the generations tested. Effects of I. fumosorosea and cell-free ethyl acetate fractions derived from the fungus on the B. tabaci fat body, ovary, and vitellogenin were also investigated. These data revealed significant deformation and degradation of ovary tissues and associated vitellogenin by the fungal mycelium as well as by cell-free ethyl acetate fungal extracts. These data indicate the lack of the emergence of resistance to I. fumosorosea under the conditions tested and demonstrate invasion of the insect reproductive tissues during fungal infection.