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Category: Biological Control

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Middleton, E.G. and I. V. MacRae. 2021. Biological Control 152: 104463, https://doi.org/10.1016/j.biocontrol.2020.104463

Wildflower plantings in agroecosystems can support arthropod predators, and may have the potential to increase conservation biological control of pest species in nearby crops. Colorado potato beetle (CPB) is a significant defoliator of potato that is resistant to many forms of management. Promoting natural enemies of CPB by establishing perennial wildflower plantings in field margins may provide a measure of control for this pest. We examined the impacts of floral plantings on the abundance of known CPB predators, predation of CPB egg masses, and CPB populations in a commercial agroecosystem. Floral plantings increased the abundance of CPB predators, but did not significantly increase the rate of predation of sentinel CPB egg masses within field margins. Within nearby potato fields, predator abundance and predation rates on CPB eggs were unaffected by the presence of flowers. Colorado potato beetle abundance in potato fields was also not impacted by floral plantings. However, floral margins may provide improved overwintering opportunities for CPB, and further investigation is needed. Perennial wildflower plantings show potential for attracting predators that prey on CPB, but these benefits do not extend into nearby potato crops.

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Miller T, Crossley MS, Fu Z, Meier AR, Crowder DW, Snyder WE. 2020. Biological Control. 151:104403.

Prey commonly must compete with conspecifics for resources while also defending themselves against predators. Both competition and defense can reduce feeding opportunities, or otherwise strain prey energy reserves, even when the prey is not killed. This suggests that stress from competition and anti-predator defense might yield non-lethal harm that differs quantitatively rather than qualitatively. We examined this possibility for an herbivorous prey species, the Colorado potato beetle (Leptinotarsa decemlineata), feeding among differing numbers of intraspecific competitors while also avoiding predation by Nabis alternatus and Hippodamia convergens. In a field cage experiment, predators and intraspecific competitors similarly reduced the herbivores’ larval survival. Yet, only exposure to predators heightened the risk of beetles later being killed by entomopathogenic nematodes and fungi, as the beetles pupated in the soil. This suggests that the threat of predation was exerting physiological harm to the prey, although it was also possible that a tradeoff existed where those beetles most resistant to predator attack were most susceptible to pathogen infection. In a second experiment, we found that regular touching of larvae by predatory Nabis or Hippodamia, in the absence of actual predation, consistently induced predator-avoidance behaviors by the larvae (e.g., rearing, vomiting, wiggling, etc.) that might be energetically costly. Indeed, only being touched by predators, but not by a wooden dowel as a disturbance control, led to greater susceptibility to entomopathogens as pupae. Altogether, our findings suggest that non-lethal interactions with predators might carry a particular cost to beetles in heightened pathogen susceptibility, not seen when facing competitors or simple disturbance. Additional work is needed to determine the specific physiological mechanism underlying this apparent synergism in the effects of predators and entomopathogens, which spans prey life stages.

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Tomilova, O. G., O. N. Yaroslavtseva, M. D. Ganina, M. V. Tyurin, E. I. Chernyak, I. V. Senderskiy, Y. A. Noskov, O. V. Polenogova, Y. B. Akhanaev, V. Yu. Kryukov, V. V. Glupov, S. V. Morozov. Journal of Insect Physiology 116: 106-117. https://doi.org/10.1016/j.jinsphys.2019.05.003

Susceptibility to the fungus Metarhizium robertsii and changes in host defences were evaluated in different stages of the intermoult period (4–6 h, 34–36 h and 84–86 h post moult in IV larval instars) of the Colorado potato beetle. A significant thickening of the cuticle during larval growth was accompanied by decreases in cuticle melanization, phenoloxidase activity and epicuticular hydrocarbon contents (C28-C32). At the same time, a decrease in the conidial adhesion rate and an increase in resistance to the fungus were observed. In addition, we recorded significant elevation of the encapsulation rate and total haemocyte counts in the haemolymph during the specified period. The activity of detoxification enzymes decreased in the haemolymph but increased in the fat body during larval growth. No significant differences in the fatty acid content in the epicuticle were observed. The role of developmental disorders in susceptibility to entomopathogenic fungi is also discussed.

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Kryukov, V. Y., M. R. Kabilov, N. Smirnova, O. G. Tomilova, M. V. Tyurin, Y. B. Akhanaev, O. V. Polenogova, V. P. Danilov, S. K. Zhangissina, T. Alikina, O. N. Yaroslavtseva, V. V. Glupov, Fungal Biology https://doi.org/10.1016/j.funbio.2019.09.012

Strains of entomopathogenic fungi may have substantial differences in their final stages of mycosis. Insect cadavers are usually overgrown with mycelium after colonization of the insect body, but in many cases, bacterial decomposition of the colonized hosts occurs. We used two Metarhizium robertsii strains in the work: Mak-1 (cadavers become overgrown with mycelium and conidia) and P-72 (cadavers decay after fungal colonization). We conducted a comparative analysis of gut and cadaver microbiota in Colorado potato beetle larvae using 16S rRNA gene sequencing after infection with these strains. In addition, we estimated the content of different forms of nitrogen in cadavers and the influence of cadavers on the growth of Solanum lycopersicum on sand substrates under laboratory conditions. It was shown that infections did not lead to a significant shift in the midgut bacterial communities of infected insects compared to those of untreated insects. Importantly, bacterial communities were similar in both types of cadaver, with predominantly enterobacteria. Decomposing cadavers (P-72) were characterized by increased nitrate and ammonium, and they had a stronger growth-promoting effect on plants compared to cadavers overgrown with mycelium and conidia (Mak-1). We also estimated the colonization and growth of plants after treatment with conidia of both strains cultivated on artificial medium. Both cultures successfully colonized plants, but strain P-72 showed stronger growth promotion than Mak-1. We propose that the use of deviant strains that are unable to sporulate on cadavers leads to a faster (though only passive) flow of nitrogen from killed insects to plants.

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García-Robles, I., De Loma, J., Capilla, M., Roger, I., Boix-Montesinos, P., Carrión, P., Vicente, M., López-Galiano, MJ, Real, MD, Rausell, C. Developmental & Comparative Immunology DOI: 10.1016/j.dci.2019.103525

Bacillus thuringiensis (Bt) toxins constitute effective, environmentally safe biopesticides. Nevertheless, insects' tolerance to Bt is influenced by environmental factors affecting immunity. To understand larval immune response in the devastating coleopteran insect pest Colorado potato beetle (CPB), we undertook a proteomic analysis of hemolymph of non-treated control larvae and larvae consuming non-lethal doses of spore-crystal mixtures containing the coleopteran-active Cry3Aa toxin. Results revealed lower amount of proteins involved in insect growth and higher amount of immune response-related proteins in challenged insects, sustaining the larval weight loss observed. Additionally, we found a potential regulatory role of the evolutionary conserved miR-8 in the insect's immune response relying on antimicrobial peptides (AMPs) production. Upon toxin challenge, different patterns of hemolymph AMPs expression and phenoloxidase activity were observed in CPB larvae reared on different Solanaceae plants. This suggests that diet and diet-associated insect midgut microbiota might modulate this insects' tolerance to non-lethal doses of Bt.

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Kryukov VY, Tomilova OG, Luzina OA, et al. Pest Manag Sci. 2018;74(3):598-606.

BACKGROUND: The search for compounds that interact synergistically with entomopathogenic fungi is aimed at enhancing the efficacy and stability of biological products against pest insects, for example, against the Colorado potato beetle (CPB). We hypothesized that fluorine-containing derivatives of usnic acid (FUA) might be candidates for the development of multicomponent bio-insecticides. The aim of this study was to analyze the co-influence of FUA and Beauveria bassiana on the survival and immune-physiological reactions of CPB larvae. RESULTS: Synergy between FUA and B. bassiana was observed after treatment of second, third and fourth larvae instars under laboratory conditions. Furthermore, synergy was observed in field trials in continental climate conditions in southeastern Kazakhstan. In a field experiment, the median lethal time was shortened three-fold, and cumulative mortality for 15 days increased by 36% in the combined treatment compared with a fungal infection alone. FUA treatment delayed larval development, decreased the total hemocyte count, and increased both the phenoloxidase activity in integuments and the detoxification enzyme rate in hemolymph. A combined treatment with fungus and FUA led to increases in the aforementioned changes. CONCLUSION: Toxicosis caused by FUA provides a stable synergistic effect between FUA and B. bassiana. The combination can be promising for the development of highly efficient products against CPB.

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Wetzel WC, Aflitto NC, Thaler JS. 2018. Ecology. 99(10):2338-2347. doi: 10.1002/ecy.2472.

A growing number of studies have manipulated intraspecific plant diversity and found dramatic changes in the densities of associated insect herbivores and their predators. While these studies have been essential for quantifying the net ecological consequences of intraspecific plant diversity, they have been less effective at uncovering the ways in which plant diversity alters trophic interactions within arthropod communities. We manipulated intraspecific plant diversity and predation risk in the field in a factorial design to reveal how a mixture of plant genotypes changes the response of an herbivorous beetle (Leptinotarsa decemlineata) to a common stink bug predator (Podisus maculiventris). We repeated the manipulations twice across the ontogeny of the beetle to examine how the effects of diversity on the predator-prey interaction differ between larval and adult stages. We found that intraspecific plant diversity, mixtures of susceptible and resistant varieties of potato (Solanum tuberosum), reduced larval survival by 20% and adult oviposition by 34%, which surprisingly put survival and oviposition lower in the mixed-genotype plots than in the resistant monocultures. Moreover, we found that predation risk reduced larval survival 25% and 11% in resistant and susceptible monocultures, respectively, but had no effect in the mixture. This result indicated that our genotypic mixing treatment interacted nonadditively with predation risk such that plant diversity altered the predator-prey interaction by changing the responses of the beetles to their stink bug predators. In addition, even though predation risk reduced larval survival, it increased adult overwintering survival by 9%, independently of plant treatment, suggesting that these interactions change through ontogeny. A key implication of our study is that plant diversity influences arthropod communities not only by changing resource quality, as past studies have suggested, but also by changing interactions between species within the arthropod community.

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Wraight SP, Ramos ME. 2017. J Invertebr Pathol. 144:47-57. doi: 10.1016/j.jip.2017.01.007.

Studies were undertaken to further characterize the previously identified synergistic activity of Bacillus thuringiensis- and Beauveria bassiana-based biopesticides against Colorado potato beetle (CPB). A flowable concentrate of B. thuringiensis morrisoni strain tenebrionis (Bt) (Novodor® FC) and a wettable powder of B. bassiana strain GHA (Bb) (Mycotrol® 22WP) were applied against CPB larval populations infesting potato in field plots. Novodor FC and an oil-dispersion formulation of Bb (Mycotrol ES) were applied against second-instar CPB larvae on potted potato plants in greenhouse tests under low relative humidity (RH), variable-temperature conditions. Each pathogen was applied alone and in combination (tank-mixed) with the other pathogen. In the field tests, each biopesticide was also combined with the spray-carrier (formulation without active ingredient) of the other pathogen. Results from the greenhouse tests showed that under warm, dry conditions, low activity of Mycotrol was counterbalanced by high activity of the Novodor, and under cool, somewhat more humid conditions, low Novodor activity was balanced by high activity of Mycotrol, with the result being a constant level of synergism (CPB mortality ca. 20 percentage points higher than predicted by independent action). Similar levels of synergism were observed under the markedly different conditions of the field and greenhouse environments, and the synergism was confirmed as arising from interaction of the two microbes, as the Bt spray carrier had no significant effect on efficacy of the Mycotrol product and the Bb spray carrier had no effect on the efficacy of Novodor. The great capacity of these two control agents to act in concert to control CPB is well documented (the fast-acting, toxic Bt acting to protect potato crops from defoliation and the slow-acting Bb reducing survival to the adult stage). These finding further underscore the strong complementary action of these agents applied jointly against CPB.

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Kryukov V, Yaroslavtseva O, Tyurin M, et al. J Invertebr Pathol. 2017;149:1-7. doi: 10.1016/j.jip.2017.07.001.

Thirty-four isolates of Metarhizium spp. from Russian collections were genotyped using 5′ EF-1α gene sequence analysis. Four species were identified, of which M. robertsii and M. brunneum were the most frequent, whereas M. anisopliae and M. pemphigum were sporadic. Radial growth studies in the temperature range of 10-40°C revealed that growth at high temperatures (35-37.5°C) was inherent for M. robertsii isolates but not for M. brunneum isolates. In contrast, M. brunneum isolates were more active at cold temperatures (10°C) compared to M. robertsii. Virulence was evaluated against larvae of the Colorado potato beetle (CPB), Leptinotarsa decemlineata Say, under two regimes: humid (21°C, 80% relative humidity (RH)) and arid (31°C, 55% RH). M. brunneum isolates were less virulent compared to M. robertsii under both regimes. M. robertsii activity did not differ under the two regimes, but M. brunneum was less virulent under the arid regime compared to the humid one. A field experiment under natural conditions (steppe zone of Western Siberia) with daily ranges of 10-43°C and 13-98% RH showed that M. robertsii was significantly more active than M. brunneum against CPB larvae.

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Yaroslavtseva ON, Dubovskiy IM, Khodyrev VP, Duisembekov BA, Kryukov VY, Glupov VV. J Insect Physiol. 2017;96:14-20. doi: 10.1016/j.jinsphys.2016.10.004.

The synergistic effect between the entomopathogenic fungus Metarhizium robertsii and a sublethal dose of the bacterium Bacillus thuringiensis ssp. morrisoni var. tenebrionis was studied in terms of immune defense reactions and detoxification system activity of the Colorado potato beetle, Leptinotarsa decemlineata, fourth instar larvae. Bacterial infection led to more rapid germination of fungal conidia on integuments. We found a significant decrease of cellular immunity parameters, including total hemocyte count and encapsulation response, under the influence of bacteria. Phenoloxidase activity in integuments was increased under bacteriosis, mycosis and combined infection compared to controls. However, phenoloxidase activity in the hemolymph was enhanced under bacteriosis alone, and it was decreased under combined infection. Activation of both nonspecific esterases and glutathione-S-transferases in the hemolymph was shown at the first day of mycosis and third day of bacteriosis. However, inhibition of detoxification enzymes was detected under combined infection. The suppression of cellular immunity and detoxification reactions in Colorado potato beetle larvae with a sublethal dose of bacteria is discussed as a reason for synergy between B. thuringiensis and M. robertsii.