Cucumber vs Ants: a Case Against the Myth of the Uses of Plant Extracts in Insect Pest Management

An accumulation of questionable scientific reports on the use of natural plant extracts to control household pest insects, using biologically irrelevant experimental designs and extremely high concentrations, has resulted in a publication bias: “promising” studies claiming readily available plants can repel various insects, including social insects, despite no usable data to judge cost-effectiveness or sustainability in a realistic situation. The Internet provides a further torrent of untested claims, generating a background noise of misinformation. An example is the belief that cucumbers are “natural” ant repellent, widely reported in such informal literature, despite no direct evidence for or against this claim. We tested this popular assertion using peel extracts of cucumber and the related bitter melon as olfactory and gustatory repellents against ants. Extracts of both fruit peels in water, methanol, or hexane were statistically significant but effectively weak gustatory repellents. Aqueous cucumber peel extract has a significant but mild olfactory repellent effect: about half of the ants were repelled relative to none in a control. While the myth may have a grain of truth to it, as cucumber does have a mild but detectable effect on ants in an artificial setup, its potential impact on keeping ants out of a treated perimeter would be extremely short-lived and not cost-effective. Superior ant management strategies are currently available. The promotion of “natural” products must be rooted in scientific evidence of a successful and cost-effective implementation prospect.

Butyl Carbitol Acetate as an Ant Repellent on the Pecan Tree Trunk

2 – (2 – butoxyethoxy) ethyl acetate (butyl carbitol acetate), an animal repellent, was found to repel red imported fire ants, Solenopsis invicta (Buren), in trail blocking, pickup, and trail to source bioassays. Butyl carbitol acetate effectively prevented worker ants from trailing up the trunk of pecan trees for 1 wk and reduced foraging for 2 wks after application. Butyl carbitol acetate and farnesol were more effective than neem extract, methyl myristate, methyl anthranilate, and Tanglefoot® (The Tanglefoot Co., Grand Rapids, Ml) in restricting ants from crossing a trunk barrier. Also, application of the repellents dissolved in wax-slurry and applied directly to the trunk was more effective than application to a wax-covered Kraft paper (Food Services Direct, Hampton, VA) band. Wax-covered strings amended with the repellents and tied around the trunk were similar in effectiveness to the waxy slurry band.