With the long-term and large-scale use, herbicides have been well known to influence tritrophic interactions particularly natural enemies of pests in agro-ecosystems. On the other hand, herbivorous insects, especially the generalist pests, have developed antagonistic interaction to different insecticides, toxic plant secondary metabolites and even heavy metals. However, whether exposure to herbicides would affect resistance of insects against insecticides is largely unknown, especially in agricultural pests. Here, we first reported that pre-exposure to two widely used herbicides butachlor and haloxyfop-methyl for 48 h can prime resistance of a generalist agricultural pest Helicoverpa armigera Hübner against insecticide methomyl and fungal toxin aflatoxin B1. In addition, there were no significant differences between control and herbicides-treated caterpillars on weight gain, pupal weight and pupation rates, suggesting that exposure to herbicides induce resistance of H. armigera accompanied with no fitness cost. Moreover, by determining detoxifying enzyme activities and toxicity bioassay with additional inhibitor of cytochrome P450 piperonyl butoxide (PBO), we showed that exposure to herbicides might prime P450-mediated detoxification of H. armigera against insecticide. Based on these results, we propose that exposure to herbicides primes resistance of H. armigera against insecticide by eliciting a clear elevation of predominantly P450 monooxygenase activities in midgut and fat body.

Polycyclic polyprenylated acylphloroglucinols (PPAPs) comprise a large group of compounds of mostly plant origin. The best-known compound is hyperforin from St. John's wort with its antidepressant, antitumor and antimicrobial properties. Chemical synthesis of PPAP variants allows the generation of compounds with improved activity and compatibility. Here we studied two synthetic PPAP-derivatives, PPAP 23 and PPAP 53, as to their antimicrobial activity. While PPAP 23 is insoluble in water, PPAP 53, the sodium salt, is water-soluble. In vitro, both compounds exhibited good and comparable activity against methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus faecium. Both compounds had no adverse effects on Galleria mellonella wax moth larvae, even at high concentrations. However, they were unable to protect the larvae from infection with S. aureus because components of the larval coelom neutralized the antimicrobial activity; a similar neutralizing effect was also seen with serum albumin. In a septic arthritis model triggered by S. aureus PPAP23 decreased the formation of abscesses and bacterial load in kidneys, and in a mouse skin abscess model topical treatment with PPAP 53 resulted in an approximately two-fold reduction in S. aureus counts. PPAP 23 and PPAP 53 also showed high growth inhibiting activity against anaerobic Gram-positive pathogenic gut bacteria such as Clostridium perfringens and Clostridium difficile. Based on these results, we envision potential application of PPAP 23 and PPAP 53 in the topical treatment of wound infections with Gram+ pathogens, and their oral use in intestinal infections with C. difficile.