Passive vectoring of entomopathogenic fungus Beauveria bassiana among the wax moth Galleria mellonella larvae by the ectoparasitoid Habrobracon hebetor females

Effects of cold storage after cold acclimation on the fitness of Habrobracon hebetor (Hymenoptera: Braconidae)

Habrobracon hebetor (Say) (Hymenoptera: Braconidae) is a cosmopolitan, idiobiont, and gregarious ectoparasitoid, which can parasitize the larvae of several pyralid and noctuid moths. However, adult parasitoids require cold storage to ensure that adequate individuals are available when a pest outbreak occurs. To understand the effects of cold storage after acclimation on offspring fitness of H. hebetor, the development, fecundity, population parameters, and paralysis rate of the F1 generation were evaluated using an age-stage, two-sex life table. Four pairing treatments were used in this study, with refrigerated males and females (ReF×ReM), unrefrigerated females and refrigerated males (UnF×ReM), refrigerated females and unrefrigerated males (ReF×UnM), and unrefrigerated females and males (UnF×UnM, control). Cold storage after acclimation had no significant effect on the fecundity or oviposition period of F0-generation H. hebetor. Moreover, the survival rate (Sa = 61.43%), proportion of females (Nf/N = 0.41), intrinsic rate of increase (r = 0.3450), finite rate of increase (λ = 1.4121), net reproduction rate (R0 = 149.47), and net paralysis rate (C0 = 74.52) of ReF×UnM and UnF×UnM (Sa = 50.00%, Nf/N = 0.34, r = 0.3297, λ = 1.3881, R0 = 155.69, C0 = 62.90, respectively) treatments were significantly higher than those of the ReF×ReM treatment (Sa = 45%, Nf/N = 0.16, r = 0.2277, λ = 1.2558, R0 = 68.81, C0 = 31.61, respectively) (except for the Sa of UnF×UnM treatment), and there was no significant difference between the 2 treatments. Overall, it is advisable to avoid simultaneous cold storage of female and male parasitoids or to add unrefrigerated males appropriately when using cold-stored parasitoids to control pests.

Biocontrol effect of entomopathogenic fungi Metarhizium anisopliae ethyl acetate-derived chemical molecules: An eco-friendly anti-malarial drug and insecticide

Insect pests represent a major threat to human health and agricultural production. With a current over-dependence on chemical insecticides in the control of insect pests, leading to increased chemical resistance in target organisms, as well as side effects on nontarget organisms, the wider environment, and human health, finding alternative solutions is paramount. The employment of entomopathogenic fungi is one such potential avenue in the pursuit of greener, more target-specific methods of insect pest control. To this end, the present study tested the chemical constituents of Metarhizium anisopliae fungi against the unicellular protozoan malaria parasite Plasmodium falciparum, the insect pests Anopheles stephensi Listen, Spodoptera litura Fabricius, and Tenebrio molitor Linnaeus, as well as the nontarget bioindicator species, Eudrilus eugeniae Kinberg. Fungal crude chemical molecules caused a noticeable anti-plasmodial effect against P. falciparum, with IC50 and IC90 values of 11.53 and 7.65 µg/mL, respectively. The crude chemical molecules caused significant larvicidal activity against insect pests, with LC50 and LC90 values of 49.228-71.846 µg/mL in A. stephensi, 32.542-76.510 µg/mL in S. litura, and 38.503-88.826 µg/mL in T. molitor at 24 h posttreatment. Based on the results of the nontarget bioassay, it was revealed that the fungal-derived crude extract exhibited no histopathological sublethal effects on the earthworm E. eugeniae. LC-MS analysis of M. anisopliae-derived crude metabolites revealed the presence of 10 chemical constituents. Of these chemicals, three major chemical constituents, namely, camphor (15.91%), caprolactam (13.27%), and monobutyl phthalate (19.65%), were highlighted for potential insecticidal and anti-malarial activity. The entomopathogenic fungal-derived crude extracts thus represent promising tools in the control of insect pests and malarial parasites.

Melanization induced by Heliothis virescens ascovirus 3h promotes viral replication

Melanization is an important innate immune defense mechanism of insects, which can kill invading pathogens. Most pathogens, for their survival and reproduction, inhibit the melanization of the host. Interestingly, our results suggested that after infection with Heliothis virescens ascovirus 3h (HvAV-3h), the speed of melanization in infected Spodoptera exigua larval hemolymph was accelerated and that the phenoloxidase (PO) activity of hemolymph in larvae infected with HvAV-3h increased significantly (1.20-fold at 96 hpi, 1.52-fold at 120 hpi, 1.23-fold at 144 hpi, 1.12-fold at 168 hpi). The transcription level of the gene encoding S. exigua prophenoloxidase-1 (SePPO-1 gene) was upregulated dramatically in the fat body during the middle stage of infection. In addition, when melanization was inhibited or promoted, the replication of HvAV-3h was inhibited or promoted, respectively. In conclusion, infection with HvAV-3h can markedly induce melanization in the middle stage of infection, and melanization is helpful for HvAV-3h viral replication.

Compatibility between the endoparasitoid Hyposoter didymator and the entomopathogenic fungus Metarhizium brunneum: a laboratory simulation for the simultaneous use to control Spodoptera littoralis

BACKGROUND

The cotton leafworm, Spodoptera littoralis, is one of the most destructive pests in the Mediterranean basin, being predominantly controlled using synthetic chemical pesticides. Strain EAMa 01/58-Su of the fungus Metarhizium brunneum and the parasitoid Hyposoter didymator are promising biological control agents for this pest. In this study, we assessed the compatibility between these two agents to control S. littoralis under joint attack scenarios.

RESULTS

Firstly, the direct and indirect effects of the fungus towards parasitoid adults were studied. The fungus significantly decreased life expectancy of the parasitoid (mortality = 62.5%; mean lethal concentration = 1.85 × 10⁶ conidia ml^-1 ; average survival time = 92.2 h) when applied at high concentrations (10⁸ conidia ml^-1 ), whereas it did not affect the reproductive potential of the parasitoid females during the 3 days after treatment. Secondly, the combinations between the two agents to control S. littoralis under different simultaneous use scenarios (inoculation of S. littoralis larvae with the fungus before being exposed to parasitoid females and vice versa) were investigated, with additive effect in all cases. A significant effect on fitness (preimaginal development time and reproductive potential) of the F1 parasitoid generation were detected. Moreover, parasitization significantly reduced the total hemocytes in S. littoralis hemolymph compared with the control, promoting fungal infection. Finally, parasitoids showed a significant preference for non-inoculated S. littoralis larvae.

CONCLUSIONS

We demonstrated compatibility (additive effect) between fungus and parasitoid under different joint attack scenarios to control S. littoralis in laboratory conditions. However, this will be supported by our ongoing greenhouse and field studies. © 2019 Society of Chemical Industry.

Pathogenic post-effect of entomopathogenic fungi on phytophagous pests and entomophagous biocontrol agents

Phytosanitary optimization of agricultural ecosystems under conditions of glasshouses and organic farming urgently demands guaranteed effect of plant protection. This can be achieved only through effective exploitation of a complex of biological agents, including arthropod predators and parasites, entomopathogenic fungi, nematodes and other microbes. Entomopathogenic fungi Beauveria bassiana and Lecanicillium muscarium are characterized by facultative parasitism and possess high potential to control phytophagous insects, including pests of vegetable crops in glasshouses. In aphids, fungal pathogenesis was found to be comprised of primary mycosis and toxigenic post-effect in a row of consequent generations. For example, L. muscarium and B. bassiana had an adverse effect on fertility and survival rates of females of aphids Aphis gossypii up to the fifth generation. The longevity, reproductive period and amount of progeny were decreased in aphids treated with water suspension of fungal conidia. It can be deduced that the post-effect is caused by toxic action of metabolites as no evident mycosis was observed in the experiments. Similar type of after-effect is observed in the lacewing Chrysopa carnea contaminated with fungal conidia. The effect is also toxigenic being most prominent in the first generation of the survivors’ progeny and traceable up to the fifth generation. The consequences of the infection are best seen in the rate adult emergence which is twice as low as compared to control. This knowledge is essential to avoid antagonism between different groups of natural enemies exploited in biological control and to design adequate technology for their application.

Habrobracon hebetor and Pteromalus cerealellae as Tools in Post-Harvest Integrated Pest Management

Consumers are increasingly demanding pesticide-free grain/legumes and processed foods. Additionally, there are more restrictions, or complete loss, of insecticides labelled for use in managing stored grain insects in post-harvest ecosystems. Suppression of post-harvest pests using parasitic wasps is a more sustainable alternative than chemical pesticides. Habrobracon hebetor (Say) (Hymenoptera: Braconidae) and Pteromalus cerealellae Ashmead (Hymenoptera: Pteromalidae) are two important parasitoids that limit economically important pests of stored products. Host searching ability and reproductive performances of H. hebetor and P. cerealellae depend on a wide range of factors, such as host species, commodities, and environmental conditions. Further, use of entomopathogens can complement the ability of parasitoids to regulate pest populations. This review provides information on aspects of H. hebetor and P. cerealellae biology and successful regulation of post-harvest pest populations.

Parasitoid envenomation alters the Galleria mellonella midgut microbiota and immunity, thereby promoting fungal infection

Gut bacteria influence the development of different pathologies caused by bacteria, fungi and parasitoids in insects. Wax moth larvae became more susceptible to fungal infections after envenomation by the ectoparasitoid Habrobracon hebetor. In addition, spontaneous bacterioses occurred more often in envenomated larvae. We analyzed alterations in the midgut microbiota and immunity of the wax moth in response to H. hebetor envenomation and topical fungal infection (Beauveria bassiana) alone or in combination using 16S rRNA sequencing, an analysis of cultivable bacteria and a qPCR analysis of immunity- and stress-related genes. Envenomation led to a predominance shift from enterococci to enterobacteria, an increase in CFUs and the upregulation of AMPs in wax moth midguts. Furthermore, mycosis nonsignificantly increased the abundance of enterobacteria and the expression of AMPs in the midgut. Combined treatment led to a significant increase in the abundance of Serratia and a greater upregulation of gloverin. The oral administration of predominant bacteria (Enterococcus faecalis, Enterobacter sp. and Serratia marcescens) to wax moth larvae synergistically increased fungal susceptibility. Thus, the activation of midgut immunity might prevent the bacterial decomposition of envenomated larvae, thus permitting the development of fungal infections. Moreover, changes in the midgut bacterial community may promote fungal killing.