Toxicity and repellency of essential oil components on the Turkestan cockroach, Blatta lateralis (Blattodea: Blattidae)

The Turkestan cockroach has become an important invasive species throughout the Southwestern United States found mostly in human dwellings as well as animal facilities. Our study aims to evaluate ecofriendly management strategies that help manage this pest. We evaluated the toxicity and repellency of six botanically-derived components against Turkestan cockroach nymphs. Compounds were diluted in acetone and nymphs were treated topically with serial dilutions between the metathoracic legs. Mortality data from each component were assessed after 24 hours post-application and subjected to probit analysis to estimate LD₅₀ values. Thymol was found to be the most toxic compound to cockroaches with a LD₅₀ of 0.34 mg/cockroach followed by trans-Cinnamaldehyde, eugenol, geraniol, methyl eugenol and p-Cymene with LD₅₀ values of 1.01, 1.56, 2.48, 3.10 and 9.85 mg/cockroach, respectively. The repellency of nymphs to dry residues of these compounds were evaluated using the Ethovision video-tracking technique. Test arena floors were divided into two halves, only one half was sprayed with the 1% of test material. Nymphal activity was recorded for 20 minutes and repellency was determined by comparing the percent time of nymphs spent in the treated zone with the activity of nymphs responding to insecticide-free arenas. Nymphs spent significantly less time in zones treated with thymol and geraniol than in untreated areas. Results from both toxicological and behavioral assays indicated that plant essential oils with a high content of thymol or geraniol are promising candidates for further field studies to fully assess their potential for use against Turkestan cockroaches.