RESUMO
Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) is a highly dispersive, polyphagous insect pest that severely defoliates crops. Excessive reliance on synthetic insecticides leads to ecological pollution and resistance development, urging scientists to probe eco-friendly biopesticides. Here, we explore the virulence of an entomopathogenic fungus, Beauveria bassiana, against S. exigua, resulting in 88% larval mortality. Using an age-stage, two-sex life table, we evaluated the lethal and sublethal effects of B. bassiana on the demographic parameters of S. exigua, including survival, development, and reproduction. Sublethal (LC20) and lethal concentrations (LC50) of B. bassiana impacted the parental generation (F0), with these effects further influencing the demographic parameters of the first filial generation (F1). The infected F1 offsprings showed a reduced intrinsic rate of increase (r), mean generation time (T), and net reproduction rate (R0). Larval developmental duration varied significantly between the control (10.98 d) and treated groups (LC20: 10.42; LC50: 9.37 d). Adults in the treated groups had significantly reduced lifespans (M: 8.22; F: 7.32 d) than the control (M: 10.00; F: 8.22 d). Reduced fecundity was observed in the B. bassiana-infected groups (LC20: 313.45; LC50: 223.92 eggs/female) compared to the control (359.55 eggs/female). A biochemical assay revealed elevated levels of detoxification enzymes (esterases, glutathione S-transferases, and acetylcholinesterase) in the F0 generation after B. bassiana infection. However, the enzymatic activity remained non-significant in the F1 generation likely due to the lack of direct fungal exposure. Our findings highlight the enduring effects of B. bassiana on the biological parameters and population dynamics of S. exigua, stressing its use in eco-friendly management programs.
RESUMO
Insect gut microbiotas have a variety of physiological functions for host growth, development, and immunity. Bacillus thuringiensis (Bt) is known to kill insect pests by releasing insecticidal protoxins, which are activated in the insect midgut. However, the interplay among Bt infection, host immunity, and gut microbiota are still unclear. Here we show that Bt Cry1Ac protoxin interacts with the gut microbiota to accelerate the mortality of P. xylostella larvae. Cry1Ac protoxin was found to cause a dynamic change in the midgut and hemocoel microbiota of P. xylostella, with a significant increase in bacterial load and a significant reduction in bacterial diversity. In turn, loss of gut microbiota significantly decreased the Bt susceptibility of P. xylostella larvae. The introduction of three gut bacterial isolates Enterococcus mundtii (PxG1), Carnobacterium maltaromaticum (PxCG2), and Acinetobacter guillouiae (PxCG3) restored sensitivity to Bt Cry1Ac protoxin. We also found that Cry1Ac protoxin and native gut microbiota can trigger host midgut immune response, which involves the up-regulation of expression of Toll and IMD pathway genes and most antimicrobial peptide genes, respectively. Our findings further shed light on the interplay between insect gut microbiota and host immunity under the Bt toxin killing pressure, and this may provide insights for improving the management of Bt resistance and lead to new strategies for biological control of insect pests.