Exploiting insect susceptibility to an essential amino acid used as an insecticide: Papilio cresphontes bioassays on methionine

The demand for alternatives to the conventional practices of pest management has increased in recent times. There is a need for control measures that are targeted, effective, and nontoxic, or of reduced toxicity to humans, mammals, birds, other non-target organisms, and the environment. Lepidopteran pests are the most damaging insects in agriculture, with the Corn Earworm, Helicoperva zea (Boddie) as possibly the most costly crop pest in America. Recently, the Southeast Asian citrus-feeding butterfly species Princeps (Papilio) demoleus was introduced into the Americas, causing an imminent threat to the citrus industry and ornamental flora. Lepidopterans maintain an alkaline midgut with aid of a transport protein, CAATCH1, which is a multi-functional cation and amino acid modulated solute transporter that also behaves as a channel for Na+, K+, and H+, with ion channel gating opened by proline and blocked by methionine. Methionine has been shown by us to disrupt aminoacid-modulated ion transport systems in lepidopterans and other insect larvae that possess an alkaline midgut.  Heraclides  (Papilio) cresphontes was bioassayed as a USDA-permitted surrogate of the Florida quarantined P. demoleus as a way to test the potential efficacy of methionine.  Larvae were allowed to feed ad libitum on wild lime plants with leaves treated with methionine. Methionine caused 100% mortality in 1st through 4th instars in a time- and dose-dependent manner, as determined by probit analysis. Proline was ineffective. Wild lime host plants did not exhibit phytotoxicity with methionine treatments during a 14 day test period. It is concluded that methionine is an effective larvicide against H. cresphontes, and therefore may be a candidate environmentally safe biorational pesticide for use against invasive P. demoleus in the Americas.