The ladybird beetle, Propylea japonica Thunberg (Coleoptera: Coccinellidae), is a widely distributed natural predator that is crucial in controlling various agricultural pests in China. Despite frequent references to its remarkable thermotolerance, the molecular mechanisms underlying its thermotolerance remain poorly understood. Here, we investigated metabolomic changes in P. japonica following exposure to acute heat stress (AHS) lasting 1 h at 39 °C and 43 °C in populations from Zhengzhou (ZZ, warm temperate climate zone) and Shenzhen (SZ, subtropical climate zone), representing distinct northern and southern Chinese ecosystems. A total of 4165 and 4151 metabolites were detected in positive and negative ion modes, respectively. The high proportion of lipid and lipid-like metabolites (35.5%) and the top 20 pathways containing the highest number of metabolites, implying membrane fluidity modulation and energy metabolism restructuring, served as the core adaptive mechanism in P. japonica populations confronting thermal stress. The SZ25 vs. SZ39 exhibited a significantly higher number of differentially expressed metabolites (DEMs), which were predominantly enriched in the purine and tryptophan metabolism pathways. This indicated that these pathways orchestrate thermal adaptation in the SZ population by coordinating energy metabolism reprogramming, orchestrating antioxidant defense mechanisms, and modulating neuroendocrine homeostasis dysregulation. Additionally, the starch and sucrose, arachidonic acid, and fructose and mannose metabolism pathways were also implicated. This study enhances our understanding of P. japonica thermotolerance and provides a valuable reference for thermotolerance mechanisms in other insects.

With the increased cultivation of Bt crops in China, Apolygus lucorum and other mirid bugs have emerged as important agricultural pests because they are insensitive to the Bt proteins. In addition, the reduction of pesticide applications after planting Bt crops also increases the severity of mirid bug outbreaks. Peristenus spretus is a parasitoid of mirid nymphs, but its sensitivity to Bt proteins is not known. In the current study, we developed a dietary exposure assay to assess the effects of Bt proteins (Cry1Ab, Cry1Ac, Cry1F, Cry2Aa, and Cry2Ab) on P. spretus adults using a diet consisting of a 10% honey solution with or without Bt proteins at 400 µg g^–1 diet. The results showed that the survival and reproduction of P. spretus adults were reduced by the cysteine protease inhibitor E-64 (a positive control) but were not affected by any of the five Bt proteins. The activities of digestive, detoxifying, and antioxidant enzymes in P. spretus were also unaffected by diets containing the Cry proteins, but they were significantly affected by the diet containing E-64. We then developed a tri-trophic bioassay to determine the effects of the five Bt proteins on P. spretus larvae and pupae. In this assay, A. lucorum nymphs fed an artificial diet containing Cry proteins were used as the hosts for P. spretus. The results of the tri-trophic assay indicated that neither the pupation rate nor the eclosion rate of the P. spretus parasitoids were significantly affected by the presence of high concentrations of Bt proteins in the parasitized A. lucorum nymphs. The overall results indicate that these two assays can be used to evaluate the toxicity of insecticidal compounds to P. spretus and that the tested Cry proteins are not toxic to P. spretus.

Propylea japonica is a widely distributed natural enemy insect that preys on aphids, whiteflies, and other pests. Owing to its exceptional environmental ad