Microbiomes of Two Pest Fly Species of Pennsylvania Mushroom Houses.

Mushroom cultivation vastly improves the yield of mushrooms under optimized, controlled conditions, but may be susceptible to opportunistic colonization by pest species that can establish themselves, as well as the pathogens and pests they may transmit. Here, we describe our investigation into the bacterial communities of adult Lycoriella ingenua (Diptera: Sciaridae) and Megaselia halterata (Diptera: Phoridae) collected from button mushroom (Agaricus bisporus) production houses in Pennsylvania. We collected adult flies and sequenced the hypervariable v4 region of the bacterial 16S rRNA using the Illumina MiSeq. The most abundant bacterial genus detected in both species was Wolbachia, but phylogenetic analysis revealed that the infections are from different clades. Future studies include the characterization of Wolbachia infections on fly behavior and biology, comparison of microbial diversity of fly species colonizing wild mushrooms, and other microbiota that may contribute to the success of certain pest fly species.

Persistence of widespread moderate Spinosad resistance among wild melon fly (Zeugodacus cucurbitae) and oriental fruit fly (Bactrocera dorsalis) populations on the major Hawaiian islands.

BACKGROUND: Insecticide resistance among invasive tephritid fruit flies poses a great risk to national food security and has the potential to disrupt quarantine and eradication programs, which rely on the efficacy of Spinosad to prevent widespread establishment in North America. During 2022 to 2023 we surveyed the extent of Spinosad resistance of two key species, oriental fruit fly Bactrocera dorsalis, and melon fly Zeugodacus cucurbitae, from 20 sites across five Hawaiian Islands including Kaua'i, O'ahu, Maui, Molokai and the "Big Island" (Hawai'i). RESULTS: We used topical thoracic applications of eight concentrations of Spinosad ranging from 0.028 to 3.6 mg/mL to evaluate the lethal concentration (LC50 and LC99) required to kill wild-caught males. Resistance ratios (RR) were calculated by comparing the LC50 of wild flies to laboratory susceptible lines maintained in colony. Our results identified at least two new sites of concern for melon fly resistance on the Big Island, and at least four sites of concern for oriental fruit fly, all of which were located on the Big Island. At these locations RRs were >5. On O'ahu, melon fly RRs were >10. CONCLUSIONS: The persistence of Spinosad resistance is concerning, yet it is a reduction compared to the values reported previously and before changes to Spinosad use recommendations by local extension agents beginning in 2017. For oriental fruit fly, these RR values are the highest levels that have been detected in wild Hawai'i populations. These data suggest that expanded Spinosad reduction and replacement programs are warranted given the ongoing issues with Spinosad resistance in Hawai'i and expansion in the number of species affected. © 2024 The Author(s). 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.

Hotter days, stronger immunity? Exploring the impact of rising temperatures on insect gut health and microbial relationships.

Climate change can generate cascading effects on animals through compounding stressors. As ectotherms, insects are particularly susceptible to variation in temperature and extreme events. How insects respond to temperature often occurs with respect to their environment, and a pertinent question involves how thermal stress integrates with insect capabilities to resolve interactions with gut microorganisms (microbiome and gut pathogens). We explore the impact of elevated temperatures and the impact of the host physiological response influencing immune system regulation and the gut microbiome. We summarize the literature involving how elevated temperature extremes impact insect gut immune systems, and how in turn that alters potential interactions with the gut microbiome and potential pathogens. Temperature effects on immunity are complex, and ultimate effects on microbial components can vary by system. Moreover, there are multiple questions yet to explore in how insects contend with simultaneous abiotic stressors and potential trade-offs in their response to opportunistic microbiota.

Helicoverpa zea-Associated Gut Bacteria as Drivers in Shaping Plant Anti-herbivore Defense in Tomato.

Insect-associated bacteria can mediate the intersection of insect and plant immunity. In this study, we aimed to evaluate the effects of single isolates or communities of gut-associated bacteria of Helicoverpa zea larvae on herbivore-induced defenses in tomato. We first identified bacterial isolates from the regurgitant of field-collected H. zea larvae by using a culture-dependent method and 16S rRNA gene sequencing. We identified 11 isolates belonging to the families Enterobacteriaceae, Streptococcaceae, Yersiniaceae, Erwiniaceae, and unclassified Enterobacterales. Seven different bacterial isolates, namely Enterobacteriaceae-1, Lactococcus sp., Klebsiella sp. 1, Klebsiella sp. 3, Enterobacterales, Enterobacteriaceae-2, and Pantoea sp., were selected based on their phylogenetic relationships to test their impacts on insect-induced plant defenses. We found that the laboratory population of H. zea larvae inoculated with individual isolates did not induce plant anti-herbivore defenses, whereas larvae inoculated with a bacterial community (combination of the 7 bacterial isolates) triggered increased polyphenol oxidase (PPO) activity in tomato, leading to retarded larval development. Additionally, field-collected H. zea larvae with an unaltered bacterial community in their gut stimulated higher plant defenses than the larvae with a reduced gut microbial community. In summary, our findings highlight the importance of the gut microbial community in mediating interactions between herbivores and their host plants.

Enemy-Risk Effects in Parasitoid-Exposed Diamondback Moth Larvae: Potential Mediation of the Interaction by Host Plants.

Enemy-risk effects (i.e., non-consumptive effects) describe the non-lethal fitness costs incurred by animals when they perceive a risk of predation. These effects can result from fear-associated changes in behavior and physiology. Diamondback moth larvae (Plutella xylostella) are known to violently wriggle backwards and drop from their host plants, usually suspending themselves with a silk thread, when threatened by predators and parasitoids. Here, we investigated the developmental costs associated with this behavior when larvae were exposed to its specialist parasitoid wasp (Diadegma insulare). Additionally, the structural and chemical properties of plants are well-known to influence predation and parasitism rates of herbivorous insects. Yet, few studies have examined the influence of plants on enemy-risk effects. Therefore, we examined the developmental costs associated with parasitism risk on two host plants. Diamondback moth larvae were placed on either cabbage or Virginia pepperweed plants and exposed to gravid parasitoids with truncated ovipositors, which prevented piercing of the host cuticle without affecting host searching and attacking behaviors. On Virginia pepperweed, risk of parasitism resulted in reduced larval weight gain, longer development time, and smaller adult size compared to larvae that were not exposed to parasitoids. However, on cabbage, parasitoid exposure prolonged development time but had no significant effects on larval weight gain and adult size. On both plants, parasitoid-exposed larvae were found feeding on older foliage than younger foliage. Our findings demonstrate that the enemy-escape behavior of diamondback moths has developmental costs and that plants may mediate the intensity of these enemy-risk effects.

Field Tests of Three Alternative Insecticides with Protein Bait for the Development of an Insecticide Rotation Program to Control Melon Flies, Zeugodacus cucurbitae (Coquillett) (Diptera: Tephritidae).

High levels of resistance to the spinosad-based insecticidal protein bait GF-120 have been detected in some populations of melon fly, Zeugodacus cucurbitae (Coquillett) (Diptera: Tephritidae), in Hawaii in 2017. To provide cucurbit farmers in Hawaii with alternative insecticides, we field-tested the effectiveness of Agri-Mek SC (a.i., abamectin), Mustang Maxx (a.i., zeta-cypermethrin), and Malathion 5EC (a.i., malathion), added to a protein bait spray (Nu-Lure Insect Bait). The insecticide and protein bait combinations were applied to the roosting plants of Z. cucurbitae around the perimeter of the cucurbit fields at one-week intervals. When individually tested, all three insecticides in combination with protein bait significantly reduced or suppressed the numbers of female flies caught in torula yeast traps. A two-week rotation of weekly applications of the three insecticides and GF-120 significantly reduced Z. cucurbitae numbers on a commercial zucchini farm on Maui. The percentage of marketable fruits harvested increased from 51% to 98% after implementing the insecticide rotation. Our findings will be used to provide cucurbit farmers with additional products to control Z. cucurbitae. The future focus will be on educating cucurbit farmers to use the insecticide rotation strategy to prevent or delay resistance development.

Spinosad resistance in field populations of melon fly, Zeugodacus cucurbitae (Coquillett), in Hawaii.

BACKGROUND: Control of Zeugodacus cucurbitae, a serious agricultural pest worldwide, often includes or is dependent on the use of spinosad-based insecticides. This is especially the case in Hawaii, where GF-120, a protein bait containing spinosad as the active ingredient, has been in use as a key integrated pest management (IPM) tool against this Tephritid for the last two decades. Here, we report on resistance to spinosad [resistance ratios (RRs) and median lethal concentration (LC50 )] in Hawaii's populations of Z. cucurbitae. RESULTS: High resistance was found in populations from three farms on Oahu (RR = 102-303; LC50  = 191-567 mg L-1 ) and in a population from Maui (RR = 8.50; LC50  = 15.9 mg L-1 ). These will be problematic for control given that the most concentrated dilution ratio on the GF-120 label is 96 mg L-1 of spinosad (1 part GF-120 to 1.5 parts water). Background resistance in a naïve wild population from the Island of Hawaii (RR = 2.73; LC50  = 5.1 mg L-1 ) was relatively low compared with a spinosad-susceptible laboratory colony (LC50  = 1.87 mg L-1 ). Resistance in the three Oahu and one Maui populations declined over generations in the absence of spinosad but remained elevated in some cases. Moreover, melon flies collected from one of the Oahu farms 1 year after the cessation of spinosad use revealed high persistence of resistance. CONCLUSION: Compared with a 2008 survey of spinosad resistance, our findings indicate a 34-fold increase in resistance on one of the Oahu farms over 9 years. The evolution and persistence of high levels of resistance to spinosad in Z. cucurbitae in Hawaii highlights the need for alternative control tactics, particularly rotation of active ingredients. © 2021 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Microbiota, pathogens, and parasites as mediators of tritrophic interactions between insect herbivores, plants, and pollinators.

Insect-associated microbes, including pathogens, parasites, and symbionts, influence the interactions of herbivorous insects and pollinators with their host plants. Moreover, herbivory-induced changes in plant resource allocation and defensive chemistry can influence pollinator behavior. This suggests that the outcomes of interactions between herbivores, their microbes and host plants could have implications for pollinators. As epizootic diseases occur at high population densities, pathogen and parasite-mediated effects on plants could have landscape-level impacts on foraging pollinators. The goal of this minireview is to highlight the potential for an herbivore's multitrophic interactions to trigger plant-mediated effects on the immunity and health of pollinators. We highlight the importance of plant quality and gut microbiomes in bee health, and how caterpillars as model herbivores interact with pathogens, parasites, and symbionts to affect plant quality, which forms the centerpiece of multitrophic interactions between herbivores and pollinators. We also discuss the impacts of other herbivore-associated factors, such as agricultural inputs aimed at decreasing herbivorous pests, on pollinator microbiomes.

Effects of Chemical Insecticide Residues and Household Surface Type on a Beauveria bassiana-Based Biopesticide (Aprehend®) for Bed Bug Management.

The biopesticide Aprehend, containing spores of the entomopathogenic fungus Beauveria bassiana, is a biological control agent for the management of the common bed bug (Cimex lectularius L.) (Hemiptera: Cimicidae). The spores are applied in strategically placed barriers, which bed bugs walk across as they search for a bloodmeal. Application of chemical insecticides by the general public and professional pest managers is common, which means that Aprehend may be sprayed on existing insecticide residues. We evaluated the effect of chemical residues, of 22 different chemical insecticides on different household surface types. We found that residues from 12 chemical pesticides significantly reduced spore viability measured 5 weeks after application in comparison to the control. However, efficacy of Aprehend, as measured by bed bug mortality and mean survival time after exposure to sprayed surfaces, seven weeks after application was not impacted detrimentally. Furthermore, in some cases, efficacy of old chemical residues was enhanced by the combination of chemical and Aprehend seven weeks after application. Surface type also played a role in the relative efficacy of all products and combinations, particularly as the residues aged.

Host permissiveness to baculovirus influences time-dependent immune responses and fitness costs.

Insects possess specific immune responses to protect themselves from different types of pathogens. Activation of immune cascades can inflict significant developmental costs on the surviving host. To characterize infection kinetics in a surviving host that experiences baculovirus inoculation, it is crucial to determine the timing of immune responses. Here, we investigated time-dependent immune responses and developmental costs elicited by inoculations from each of two wild-type baculoviruses, Autographa californica multiple nucleopolyhedrovirus (AcMNPV) and Helicoverpa zea single nucleopolyhedrovirus (HzSNPV), in their common host H. zea. As H. zea is a semi-permissive host of AcMNPV and fully permissive to HzSNPV, we hypothesized there are differential immune responses and fitness costs associated with resisting infection by each virus species. Newly molted 4th-instar larvae that were inoculated with a low dose (LD15 ) of either virus showed significantly higher hemolymph FAD-glucose dehydrogenase (GLD) activities compared to the corresponding control larvae. Hemolymph phenoloxidase (PO) activity, protein concentration and total hemocyte numbers were not increased, but instead were lower than in control larvae at some time points post-inoculation. Larvae that survived either virus inoculation exhibited reduced pupal weight; survivors inoculated with AcMNPV grew slower than the control larvae, while survivors of HzSNPV pupated earlier than control larvae. Our results highlight the complexity of immune responses and fitness costs associated with combating different baculoviruses.

Biology of Mushroom Phorid Flies, Megaselia halterata (Diptera: Phoridae): Effects of Temperature, Humidity, Crowding, and Compost Stage.

The mushroom phorid fly, Megaselia halterata (Wood), is a common pest of mushroom production in many parts of the world. Due to the reduced availability of conventional insecticides for mushroom production, M. halterata has recently developed into a major pest in the top mushroom-producing county in the United States (Chester County, PA). Mushrooms are grown entirely indoors, and though larval development of M. halterata occurs in the mushroom-growing substrate, adult flies have been captured both inside and outside of the facilities. Here, we investigated three factors that might contribute to their growth and development. 1) The effects of ambient temperature (15-30°C) and relative humidity (RH; 21-98%) on adult M. halterata lifespan, 2) the effect of spawned compost stage (freshly inoculated with spawn vs 14-d spawned compost) on reproductive output, and 3) the effect of population density on reproductive output. The longevity of adult M. halterata increased under cooler temperatures and more humid conditions (>75% RH), which reflect the conditions inside mushroom-growing facilities. Similar numbers of flies emerged from freshly inoculated and 14-d spawned compost, but flies emerged earlier from 14-d spawned compost. The higher the parental fly density, the more offspring emerged from spawned compost, but the positive relationship reached a plateau beyond 40 parental mating pairs per 100 g of compost. Our findings highlight relevant abiotic and biotic factors that may contribute to M. halterata population dynamics.

Efficacy of a Fungal Biopesticide for Bed Bug Management Is Influenced by the Toxicity and Associated Behavioral Avoidance of Harborages on Insecticide-Impregnated Box Spring Covers.

Bed bugs spend most of their lives hiding in harborages, usually in the seams of mattresses and box springs and in crevices of bed frames. For insecticidal products that target these shelters, the repellency of the products for bed bugs may influence their duration of contact. Bed bugs are known to avoid contacting surfaces treated with certain insecticides. The fungal biopesticide Aprehend contains spores of the entomopathogen, Beauveria bassiana. It is sprayed around bed frames, box springs, and furniture where bed bugs are likely to walk, which includes potential shelters. Here, I investigated the influence of a permethrin-impregnated cover, ActiveGuard, on bed bug sheltering behavior and the effectiveness of combining ActiveGuard with Aprehend. Bed bugs avoided harboring in a shelter constructed with ActiveGuard compared to a nontoxic encasement-type cover. This avoidance behavior reduced mortality induced by ActiveGuard shelters compared to forced continuous contact on the ActiveGuard cover. However, while bed bugs also avoided Aprehend-treated ActiveGuard shelters, the combined treatment induced almost complete mortality and more quickly than Aprehend-treated shelters made of the encasement-type cover. This suggests compatibility between the two integrated pest management (IPM) tools even though the bed bug's avoidance behavior would suggest otherwise. Since Aprehend is highly effective against pyrethroid-resistant bed bugs, its use would provide more effective control where bed bug populations are more resistant to the permethrin-impregnated cover.

The impact of baculovirus challenge on immunity: The effect of dose and time after infection.

Understanding how hosts respond to pathogen attack is crucial to disease management. The response of a host can be particularly important if hosts have to defend against multiple pathogens which could either benefit from or be suppressed by prior pathogen exposure. Insect defence against viruses is less well understood than responses to other entomopathogens and much of the information available relates to in vitro studies and model systems. Baculoviruses are natural pathogens of insects, particularly Lepidoptera, and have been well-studied in terms of their ecology, pest control potential and molecular biology. In order to examine how an insect reacts to baculovirus challenge, we measured components of the cellular and humoral immune response of the cabbage looper Trichoplusia ni to Trichoplusia ni SNPV, a narrow-host range nucleopolyhedrovirus (NPV), over four doses and three times after pathogen challenge (18, 42 and 90 h). We found that total haemocyte numbers peaked at 42 h post-exposure at all doses, and declined linearly with increasing dose after the 18 h time point. Two immune-related enzymes, phenoloxidase (PO) and FAD-glucose dehydrogenase (GLD), showed very different responses. PO levels were lowest at the 42 h time point and were not influenced by virus dose when each time point was examined separately. GLD levels declined over time but they interacted with virus dose in a non-linear manner, such that there was an increase in levels at intermediate virus doses after 18 h, no effect at 42 h, and then declined as infection progressed at 90 h post-infection. These data suggest that baculoviruses can rapidly infect haemocytes (or cause a reduction in their numbers) in a dose-dependent manner once the infection is systemic, likely reducing the ability of the host to counter subsequent infections. However, the data do not support a direct role for PO in defence against baculoviruses. Whether GLD plays a role in virus defence is still unclear.

Plant defenses interact with insect enteric bacteria by initiating a leaky gut syndrome.

Plants produce suites of defenses that can collectively deter and reduce herbivory. Many defenses target the insect digestive system, with some altering the protective peritrophic matrix (PM) and causing increased permeability. The PM is responsible for multiple digestive functions, including reducing infections from potential pathogenic microbes. In our study, we developed axenic and gnotobiotic methods for fall armyworm (Spodoptera frugiperda) and tested how particular members present in the gut community influence interactions with plant defenses that can alter PM permeability. We observed interactions between gut bacteria with plant resistance. Axenic insects grew more but displayed lower immune-based responses compared with those possessing Enterococcus, Klebsiella, and Enterobacter isolates from field-collected larvae. While gut bacteria reduced performance of larvae fed on plants, none of the isolates produced mortality when injected directly into the hemocoel. Our results strongly suggest that plant physical and chemical defenses not only act directly upon the insect, but also have some interplay with the herbivore's microbiome. Combined direct and indirect, microbe-mediated assaults by maize defenses on the fall armyworm on the insect digestive and immune system reduced growth and elevated mortality in these insects. These results imply that plant-insect interactions should be considered in the context of potential mediation by the insect gut microbiome.

Persistence and Lethality of a Fungal Biopesticide (Aprehend) Applied to Insecticide-impregnated and Encasement-type Box Spring Covers for Bed Bug Management.

The newly developed fungal biopesticide Aprehend, containing spores of Beauveria bassiana, is the first biological control agent to be incorporated into management programs to control the common bed bug (Cimex lectularius L.) (Hemiptera: Cimicidae). Aprehend is sprayed as barriers where bed bugs are likely to walk and pick up spores as they search for a bloodmeal. A key application target for Aprehend is the box spring, which may be covered by encasement-type or insecticide-impregnated covers. Since some insecticides can reduce the persistence of fungal spores, we tested the efficacy and spore germination percentages of Aprehend when applied to the two types of box spring covers. We found that spore germination was about 11% lower on the permethrin-impregnated ActiveGuard cover than on the encasement-type AllerEase cover. However, bed bugs exposed for 15 min to Aprehend on the two box spring covers suffered similarly high levels of mortality irrespective of the cover material. Thus, there was no inhibitory or additive effect of the ActiveGuard cover on bed bug mortality. Lastly, overall mortality was higher if bed bugs were exposed to Aprehend-treated ActiveGuard than the ActiveGuard cover alone. Our findings indicate that if pest managers are using ActiveGuard covers in combination with Aprehend, best practice would be to use ActiveGuard on mattresses and apply Aprehend directly to the box spring or to a box spring covered by an encasement-type cover.

Pathogen-Mediated Tritrophic Interactions: Baculovirus-Challenged Caterpillars Induce Higher Plant Defenses than Healthy Caterpillars.

Although the tritrophic interactions of plants, insect herbivores and their natural enemies have been intensely studied for several decades, the roles of entomopathogens in their indirect modulation of plant-insect relationships is still unclear. Here, we employed a sublethal dose of a baculovirus with a relatively broad host range (AcMNPV) to explore if feeding by baculovirus-challenged Helicoverpa zea caterpillars induces direct defenses in the tomato plant. We examined induction of plant defenses following feeding by H. zea, including tomato plants fed on by healthy caterpillars, AcMNPV-challenged caterpillars, or undamaged controls, and subsequently compared the transcript levels of defense related proteins (i.e., trypsin proteinase inhibitors, peroxidase and polyphenol oxidase) and other defense genes (i.e., proteinase inhibitor II and cysteine proteinase inhibitor) from these plants, in addition to comparing caterpillar relative growth rates. As a result, AcMNPV-challenged caterpillars induced the highest plant anti-herbivore defenses. We examined several elicitors and effectors in the secretions of these caterpillars (i.e., glucose oxidase, phospholipase C, and ATPase hydrolysis), which surprisingly did not differ between treatments. Hence, we suggest that the greater induction of plant defenses by the virus-challenged caterpillars may be due to differences in the amount of these secretions deposited during feeding or to some other unknown factor(s).

Jasmonic acid-induced plant defenses delay caterpillar developmental resistance to a baculovirus: Slow-growth, high-mortality hypothesis in plant-insect-pathogen interactions.

Plants damaged by herbivore feeding can induce defensive responses that reduce herbivore growth. The slow-growth, high-mortality hypothesis postulates that these non-lethal plant defenses prolong the herbivore's period of susceptibility to natural enemies, such as predators and parasitoids. While many juvenile animals increase their disease resistance as they grow, direct tests of the slow-growth, high-mortality hypothesis in the context of plant-herbivore-pathogen interactions are lacking. Caterpillars increase their resistance to lethal baculoviruses as they develop within and across instars, a phenomenon termed developmental resistance. Progression of developmental resistance can occur through age-related increases in systemic immune functioning and/or midgut-based resistance. Here, we examined the slow-growth, high-mortality hypothesis in the context of developmental resistance of caterpillars to baculoviruses. Intra-stadial (within-instar) developmental resistance of the fall armyworm, Spodoptera frugiperda, to an oral inoculum of the baculovirus SfMNPV increased more rapidly with age when larvae were fed on non-induced foliage than foliage that was induced by jasmonic acid (a phytohormone that up-regulates plant anti-herbivore defenses). The degree of developmental resistance observed was attributable to larval weight at the time of virus inoculation. Thus, slower growth on induced plants prolonged the window of larval susceptibility to the baculovirus. Developmental resistance on induced and non-induced plants was absent when budded virus was injected intrahemocoelically bypassing the midgut, suggesting that developmental resistance was gut-based. Addition of fluorescent brightener, which weakens midgut-based resistance mechanisms to oral virus challenge, abolished developmental resistance. These results highlight the impact of plant defenses on herbivore growth rate and consequences for disease risk.

Herbivore-Induced Defenses in Tomato Plants Enhance the Lethality of the Entomopathogenic Bacterium, Bacillus thuringiensis var. kurstaki.

Plants can influence the effectiveness of microbial insecticides through numerous mechanisms. One of these mechanisms is the oxidation of plant phenolics by plant enzymes, such as polyphenol oxidases (PPO) and peroxidases (POD). These reactions generate a variety of products and intermediates that play important roles in resistance against herbivores. Oxidation of the catecholic phenolic compound chlorogenic acid by PPO enhances the lethality of the insect-killing bacterial pathogen, Bacillus thuringiensis var. kurstaki (Bt) to the polyphagous caterpillar, Helicoverpa zea. Since herbivore feeding damage often triggers the induction of higher activities of oxidative enzymes in plant tissues, here we hypothesized that the induction of plant defenses would enhance the lethality of Bt on those plants. We found that the lethality of a commercial formulation of Bt (Dipel® PRO DF) on tomato plants was higher if it was applied to plants that were induced by H. zea feeding or induced by the phytohormone jasmonic acid. Higher proportions of H. zea larvae killed by Bt were strongly correlated with higher levels of PPO activity in the leaflet tissue. Higher POD activity was only weakly associated with higher levels of Bt-induced mortality. While plant-mediated variation in entomopathogen lethality is well known, our findings demonstrate that plants can induce defensive responses that work in concert with a microbial insecticide/entomopathogen to protect against insect herbivores.

Tritrophic Interactions: Microbe-Mediated Plant Effects on Insect Herbivores.

It is becoming abundantly clear that the microbes associated with plants and insects can profoundly influence plant-insect interactions. Here, we focus on recent findings and propose directions for future research that involve microbe-induced changes to plant defenses and nutritive quality as well as the consequences of these changes for the behavior and fitness of insect herbivores. Insect (herbivore and parasitoid)-associated microbes can favor or improve insect fitness by suppressing plant defenses and detoxifying defensive phytochemicals. Phytopathogens can influence or manipulate insect behavior and fitness by altering plant quality and defense. Plant-beneficial microbes can promote plant growth and influence plant nutritional and phytochemical composition that can positively or negatively influence insect fitness. Lastly, we suggest that entomopathogens have the potential to influence plant defenses directly as endophytes or indirectly by altering insect physiology.