Temperature dependent immunological responses of Spoladea recurvalis exposed to entomopathogenic fungi

Abstract

Spoladea recurvalis is a major pest of amaranth, capable of causing up to 100% yield loss if not controlled. Current control measures rely on synthetic chemicals; however, these chemicals are unsafe due to the crop’s short maturity that make pre-harvest intervals observation difficult. A sustainable alternative to synthetic chemicals would be entomopathogenic fungi (EPF) though, a few bottlenecks still exist in the effective use of these biological solutions. Studies show low susceptibility of S. recurvalis to Metarhizium anisopliae isolates ICIPE 30 and ICIPE 18, with larval mortalities of 58.3 and 6.7%, respectively. Temperature can affect the efficacy of EPF and how the insect’s immunity responds to fungal infections, but the effect of temperature on S. recurvalis and their interactions with the EPF is unknown. Therefore, we evaluated immune responses and gut microbiome of S. recurvalis when exposed to EPF at 15, 20, 25, 30 and 35 °C. From the results, S. recurvalis susceptibility increased at 30 °C, with ICIPE 30 causing the strongest effect. Total hemocyte counts in ICIPE 30-treated larvae reduced from 30.25 × 104/ml on day 3 to 10.75 × 104/ml on day 7. Granulocytes and plasmatocytes also decreased significantly. The dominant bacterial genera were Enterobacter, Enterococcus, and Klebsiella, with microbial diversity highest in ICIPE 30-treated larvae on day 1 and ICIPE 18-treated larvae on day 7, and lowest in ICIPE 30-treated larvae on day 7. The Findings of this study demonstrate that temperature influences this EPF’s efficacy and provide important information on the optimal conditions for this biopesticide in the pest’s management.