The objective of this project was to identify one or more chemical compounds that could serve as an attractant to invasive Brown Treesnakes (Boiga irregularis) smaller than 700 mm snout-vent length.
This project extracted skin compounds from geckos (Hemidactylus frenatus), a preferred prey of small Brown Treesnakes, and used bioassays to identify which of the successively more purified extract fractions contained compounds attractive to the snakes. Chemical analyses followed to characterize compounds in fractions of interest. For the study to be classified as a success, one or a few dominant compounds in a fraction needed to be identified that had a clear and consistent attraction effect on the snakes; this (these) compound(s) would be strong candidates for snake attractants if they are commercially available or possible to synthesize in a cost-effective manner.
Many snakes did not respond to either treatments or controls. Of those snakes that did respond, the majority responded to the treatment with gecko scent rather than to controls. In one experiment, all snakes that responded did so to a crude, non-fractionated gecko extract; they ingested or chewed on pieces of eraser scented with the extract (but not un-scented control erasers). In another experiment, several snakes responded exclusively to erasers scented with one out of two fractions resulting from a first extract separation step. However, after separating the bioactive fraction one step further, this study detected no attraction to any of the three resulting subfractions. Gas chromatography-mass spectrometry identified cholesterol as the dominant component in the bioactive fraction in addition to other compounds (e.g., fatty acids and hydrocarbons), which occurred in smaller amounts. The snake attraction effect of pure cholesterol has yet to be verified, and it is unknown if the addition of other compounds would enhance its attraction effect, but the results provide a proof-of-concept for extraction, purification, testing, and analysis of chemical compounds acting as attractants to small Brown Treesnakes. Cholesterol is commercially available at a low cost.
Finding a non-animate attractant for the Brown Treesnake—a costly invasive pest that has devastated Guam’s avifauna and poses a severe threat to other islands—would greatly facilitate its containment in Guam as well as help eradicate it in Guam and any other locations it may appear. This is especially true for attractants suitable for small snakes, as they have proven resistant to the current rodent-based control techniques. Their favored gecko prey is logistically difficult to use in large-scale operational control. Finding a cheap, non-animate compound that could help lure small snakes into traps, or be used to scent matrices for oral toxicants, would be a major step forward for Brown Treesnake control. The results demonstrated that it is possible to identify chemical components in fractionated gecko extracts that elicit a feeding response in Brown Treesnakes. Further research and development would need to involve identification of compounds that occurred in minor amounts, and screening for snake attraction efficacy of cholesterol as well as mixes of compounds.