Risk assessment of predatory lady beetle Propylea japonica's multi-generational exposure to three non-insecticidal agrochemicals

Abstract

The effects of non-insecticidal agrochemicals on pest natural predators remain largely unexplored except bees and silkworm. The herbicide quizalofop-p-ethyl (QpE), fungicide thiophanate-methyl (TM), and plant growth regulator mepiquat chloride (MC) have been extensively applied as non-insecticidal agrochemicals. Here, we systematically evaluated multiple effects of these 3 non-insecticidal agrochemicals on three generations of Propylea japonica, an important agroforestry predatory beetle, including the effects on its development, reproduction, enterobacteria, and transcriptomic response. The results showed that QpE exhibited a hormetic effect on P. japonica, thus significantly increasing the survival rate of generation 2 (F2) females, generation 3 (F3) females, and F3 males and body weight of F3 males. However, three successive generations exposed to TM and MC had no significant effect on longevity, body weight, survival rate, pre-oviposition period, and fecundity of P. japonica. Additionally, we investigated the effects of MC, TM, and QpE exposure on gene expression and gut bacterial community of F3 P. japonica. Under MC, TM, and QpE exposure, the overwhelming genes of P. japonica (99.90 %, 99.45 %, and 99.7 %) remained unaffected, respectively. Under TM and MC exposure, differentially expressed genes (DEGs) were not significantly enriched in any KEGG pathway, indicating TM and MC did not significantly affect functions of P. japonica, but under QpE exposure, the expression levels of drug metabolism-related genes were down-regulated. Although QpE treatment did not affect gut dominant bacterial community composition, it significantly increased relative abundances of detoxification metabolism-related bacteria such as Wolbachia, Pseudomonas and Burkholderia in P. japonica. However, TM and MC had no significant effect on the gut bacterial community composition and relative abundance in P. japonica. This study revealed for the first time the mechanism by which P. japonica might compensate for gene downregulation-induced detoxification metabolism decline through altering symbiotic bacteria under QpE exposure. Our findings provide reference for the rational application of non-insecticidal agrochemicals.

Keywords: Mepiquat chloride; P. japonica; Quizalofop-p-ethyl; Safety evaluation; Thiophanate-methyl.