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Pesticide Biochemistry and Physiology

Geranium intoxication induces detoxification enzymes in the Japanese beetle, Popillia japonica Newman

Adekunle W.Adesanya, David W.Held, Nannan Liu

Department of Entomology and Plant Pathology, Auburn University, 301 Funchess Hall, Auburn, AL 36830, United States.


Popillia japonica is a generalist herbivore that feeds on > 300 host plant species in at least 72 plant families. It is unknown why P. japonica, despite possessing active detoxification enzymes in its gut, is paralyzed when feeding on the petals of one of its preferred host plant, Pelargonium × hortorum, or on artificial diet containing quisqualic acid (QA), the active compound in zonal geranium. We hypothesized that Pelargonium × hortorum or QA do not induce activity of the cytochrome P450, glutathione S transferase (GST), and carboxylesterase (CoE) detoxification enzymes in P. japonica. In this study, P. japonica were fed petals of zonal geranium or agar plugs containing QA, or rose petals, another preferred but non-toxic host. Midgut enzyme activities of P450, GST, and CoE were then assayed after 6, 12, or 24 h of feeding. In most cases, P450, GST, and CoE activities were significantly induced in P. japonica midguts by geranium petals and QA, though the induction was slower than with rose petals. Induced enzyme activity reached a peak at 24 h after consumption, which coincides with the period of highest recovery from geranium and QA paralysis. This study shows that toxic geranium and QA induce detoxification enzyme activity, but the induced enzymes do not effectively protect P. japonica from paralysis by QA. Further investigation is required through in vitro studies to know if the enzymes induced by geranium are capable of metabolizing QA. This study highlights a rare physiological mismatch between the detoxification tool kit of a generalist and its preferred host.

Graphical abstract

Keywords: Quisqualic acid, P450 activity, GST activity, Carboxylesterase activity, Allelochemical toxicity, Biopesticide.

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