Geranium intoxication circumvents detoxification enzymes in Japanese beetles, Popillia japonica Newman

Adult Japanese beetles are generalist herbivores, which feed on >300 host plant species in at least 72 plant families. Beetles become paralyzed when they feed on petals of zonal geranium (Pelargonium × hortorum Bailey), a preferred host plant. Japanese beetles possess a suite of inducible detoxification enzymes for metabolizing plant toxins.  Quisqualic acid, the active compound in geranium, is responsible for paralysis of Japanese beetles. However, quisqualic acid may circumvent or not induce detoxification enzymes in Japanese beetles. Hence, the goal of this research was to study the connection between geranium (quisqualic acid) intoxication and the activity of cytochrome P450 (P450), glutathione S transferase (GST) and carboxylesterase (CoE) proteins in the midgut of adult Japanese beetles. Beetles were fed toxic petals of geranium or agar plugs containing quisqualic acid at different time periods and assayed for midgut enzyme activities.  Geranium and quisqualic acid induced activity of P450, GST and CoE in beetles’ midgut. Paralysis of the beetles was greatest at 12h, yet there were significantly higher enzyme activities at 24h, coincident with recovery of the beetles.  Our study suggests that induction of detoxification enzymes by toxic geranium and quisqualic acid does not completely protect Japanese beetles from being paralyzed by geranium. Further investigation is required through in vitro studies to know if the enzymes induced by geranium are capable of metabolizing quisqualic acid.