BACKGROUNDPlants emit volatile organic compounds (VOCs), which serve as critical cues for herbivorous insects to locate hosts for feeding and oviposition. Understanding how adults identify host plants is essential to develop pest management strategies, particularly for hemiedaphic insects like click beetles, the larvae of which are significant soil-dwelling pests. To investigate click beetle attraction towards plant VOCs and their relevance for oviposition, we tested the attractiveness of constitutive VOCs (emitted by intact plants) and damage-induced VOCs (released by chopped plants) from 11 plant species to male and female Agriotes sputator beetles.RESULTSAgriotes sputator beetles exhibit plant species-specific olfactory preferences, which are influenced by beetle sex and female maturity and differ between constitutive and damage-induced VOCs. Female beetles showed the greatest attraction to buckwheat VOCs, especially during their main oviposition period, whereas males were more attracted to clover and ryegrass. EAG recordings show strong female antennal responses to ryegrass, carrot, maize, wild carrot, barley, and buckwheat VOCs, while male antennae responded significantly only to peas. Antennae from female beetles show overall stronger responses to constitutive VOCs than those of males (P = 0.02).CONCLUSIONThese findings facilitate the development of new approaches for Agriotes pest management. Understanding preferred plant VOCs aids in identifying attractive semiochemicals that can be used for monitoring female beetles. Additionally, recognizing attractive plants aids wireworm management by either avoiding them in crop rotations before sensitive crops (thus reducing oviposition) or by attracting beetles to specific areas where they can be targeted by control measures. (c) 2025 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Theories have been widely proposed and tested for impacts of soil nitrogen (N) on phytochemical defenses. Among the hundreds of distinct cardenolide toxins produced by milkweeds (Asclepias spp.), few contain N, yet these appear to be the most toxic against specialist herbivores. Because N- and non-N-cardenolides coexist in milkweed leaves and likely have distinct biosynthesis, they present an opportunity to address hypotheses about drivers of toxin expression. We tested effects of soil N and herbivore-damage on cardenolide profiles of two milkweed species differing in life-history strategies (Asclepias syriaca and A. curassavica), and the toxicity of their leaves. In particular leaf extracts were tested against the target enzymes (Na+/K+-ATPase extracted from neural tissue) from both monarch butterflies (Danaus plexippus) as well as less cardenolide-resistant queen butterflies, D. gilippus. Increasing soil N enhanced biomass of Asclepias syriaca but had weak effects on cardenolides, including causing a significant reduction in the N-cardenolide labriformin; feeding by monarch caterpillars strongly induced N-cardenolides (labriformin), its precursors, and total cardenolides. Conversely, soil N had little impact on A. curassavica biomass, but was the primary driver of increasing N-cardenolides (voruscharin, uscharin and their precursors); caterpillar induction was weak. Butterfly enzyme assays revealed damage-induced cardenolides substantially increased toxicity of both milkweeds to both butterflies, swamping out effects of soil N on cardenolide concentration and composition. Although these two milkweed species differentially responded to soil N with allocation to growth and specific cardenolides, leaf toxicity to butterfly Na+/K+-ATPases was primarily driven by herbivore-induced defense. Thus, both biotic and abiotic factors shape the composition of phytochemical defense expression, and their relative importance may be dictated by plant life-history differences.