Oral toxicity of chitin synthesis inhibitors (CSIs) and plant extracts to rubber termite, Coptotermes curvignathus Holmgren (Rhinotermitidae: Isoptera)

Aran Ngampongsai, Surakrai Permkam, Wisut Sittichaya, Suraphong Saiboon and Kanok Maharat

Abstract: Coptotermes curvignathus (Holmgren) causes serious damage to live rubber trees in Thailand. Chemicals have been commonly used to control this termite. The control of this subterranean termite by soil treatments remains problematic, so the oral toxicities in a bait formulation of chitin synthesis inhibitors (CSIs), plant oils and crude extracts were evaluated to find environmentally friendly and safe products for the control. Baits made of cardboard mixed with various concentrations of the tested solutions of CSIs, plant oils, and crude extracts were ingested by worker termites. Ten worker termites were used for each concentration with five replications. Mortality was recorded and LC50 was estimated by probit analysis at 24, 48, 72, 96 and 120 h after treatment. Lufenuron was the most toxic to C. curvignathus with the lowest oral LC50 of 323.7 ppm at 120 h. The oral LC50 values of flufenoxuron, buprofezin, chlorfluazuron and novaluron were 505.6, 830.6, 1054.3 and 2 939.8 ppm, respectively. Oils from long pepper (Piper retrofractum Vahl), black pepper (Piper nigrum L.), and thiam [Azadirachta excelsa (Jack) Jacobs] were highly toxic to C. curvignathus, reaching 100% mortality after exposure for 120 h at the concentrations of 2 000, 2 500 and 3 000 ppm, respectively. Plant oils exhibited greater toxicity than plant crude extracts. Oral LC50 values of the plant oils were 4 382.6, 7 507.6 and 5 618.3, ppm, while those of plant crude extracts were 12 032.4, 12 630.6 and 23 860.6 ppm, in the same order. In conclusion, the long pepper oil and lufenuron have potential for the control of this termite species, to reduce or replace synthetic chemicals in future soil treatments. However, field trials should be done to confirm the efficacy of the product in fully realistic conditions.

Keywords: plant oils, plant crude extracts, Coptotermes curvignathus, oral LC50, baits

Date published: 2020-10-16