Geranium Intoxication and Consequence on Detoxification Enzymes in a Polyphagous Scarab, Popillia japonica Newman

Adult Japanese beetles, Popillia japonica Newman (Scarabaeidae) are one of the most polyphagous insect herbivores feeding on over 300 host plants representing 72 plant families, with limited fitness consequences. However, flowers of zonal geranium (Pelargonium × hortorum L. G. Bailey), a highly preferred host for Japanese beetles, contain quisqualic acid, which paralyzes and can kill adult Japanese beetles following one feeding bout. Japanese beetles, like other insect herbivores, rely on detoxification enzymes to circumvent plant allelochemicals. Therefore this study investigated if quisqualic acid, in artificial diet or in planta, induces three major superfamilies of detoxification enzymes (cytochrome P450, glutathione S transferase and carboxylesterase) in the midgut of adult Japanese beetles. We predict that quisqualic acid will induce a limited or delayed response of these enzyme groups. Beetles were allowed to consume petals of zonal geranium or agar plugs containing 10µg quisqualic acid. Midguts were dissected from live, but paralyzed beetles, with live beetles either starved or fed rose petals used as negative and positive control groups. Enzyme activities were assayed using multiple chemical substrates for each enzyme for the treatment and control groups. The results of these experiments and their relevance to Japanese beetle’s physiology and ecology will be discussed.