Insecticidal activity of Thai botanical extracts against German cockroach, Blattella germanica (l.) (Orthoptera : Blattellidae)

Abstract

German cockroach, B. germanica is considered an important medical and economic pest in Thailand because they can carry many pathogens, such as bacteria, virus and protozoa to humans. The objective of this study was to evaluate the efficacy of extracts derived from six Thai botanicals, which including Piper retrofractum, Stemona tuberosa, Derris elliptica, Rhinacanthus nasutus, Butea superba and Foeniculum vulgare against various developmental stages of B. germanica under laboratory conditions.

Different concentrations of extract derived from six Thai botanical (2, 4, 6, 8 and 10%) (% w/v) were used to exposure to various developmental stage including nymphs, adult and gravid females stage of B. germanica by topical application method. The mortality was assessed at 1, 2, 4, 6, 24 and 48 hours after the exposure. Data was statistically analyzed by using analysis of variance (ANOVA) and Duncan’s multiple range test (DMRT). LD50 were calculated by the Probit analysis program. Moreover, the major component of Thai botanical extract that had highest insecticidal activity was analyzed by column chromatography and thin layer chromatography (TLC).

The results showed that Thai botanical extracts derived from P. retrofractum have the highest mortality on various developmental stage of B. germanica at every experimental time intervals. Moreover, the acetone extract of P. retrofractum at highest concentration (10% w/v) showed complete insecticidal activity (100%) against both adult (LD50 2.61) and gravid females stages (LD50 1.97) of B. germanica after 6 hours post exposure. The fraction 5 of acetone extract of P. retrofractum obtained from TLC analysis was showed highest efficacy against B. germanica and the major component was identified as piperine.

Therefore, extracts of P. retrofractum can be used as an alternative natural insecticide for the controlling of B. germanica which are inexpensive and safe for humans and the environment. However, insecticidal activity of the Thai botanical extracts against B. germanica in field environment and appropriate formulations of this extracts should be determined.