Screening of Plant Extracts Possessing Methylenedioxyphenyl (MDP) Group as Potential Synergists in Insecticide Formulations using the Maize Weevil, Sitophilus Zea-mais (Motsch.)

Synergists are compounds that are either negligibly toxic or non-toxic to insects when applied on their own, but enhance the efficacy of an insecticide. Many insects are able to detoxify insecticide molecules and survive their application. Early studies found that most methylene-dioxyphenyl (MDP) agents themselves possess relatively low intrinsic toxicity, but strongly influence the actions of other xenobiotic in mammals and insects. The current commercial synergist, Piperonyl butoxide (PBO), though effective as a synergist, is not classified as an organic product in many countries. With the current focus on decreasing environmental contamination and increasing demand for organic products, a natural compound for use as a synergist would be ideal. Searches for effective synergists have not yet yielded many compounds that have the viability equivalent to that of PBO. This paper screened plant extracts possessing MDP rings as potential synergists in insecticides formulations using the maize weevil, Sitophilus zea-mais. Dose-mortality experiments were carried out on S. zea-mais at four concentrations of synergists. Topical application of synergist on S. zea-mais was done in triplicate in a CRD. Experiments were conducted under controlled laboratory conditions of 27 ± 2OC and 60 ± 5%RH with normal daylight hours. Analysis of Variance (ANOVA) was used to obtain the mean mortality differences of S. zea-mais at P ≤ 0.05 while Duncan’s Multiple Range Test (DMRT) was used to rank significant concentration means within a synergist. Black pepper seed hexane extract (BPSHE) and PBO after 48 h exposure were statistically significant (P ≤ 0.05) with the average percentage mortalities of 10% and 20% at 10,000 ppm and 20,000 ppm respectively, while PBO and Coriander leaves hexane extract (CLHE) were significant P ≤ 0.05 after 72 h. PBO was the most toxic synergist (36.67 ± 3.33%) followed by CLHE (26.67 ± 3.43%) at 20,000 ppm. It can be concluded that the plant extracts tested and statistically significant at a particular exposure time can be used to replace the standard PBO in insecticide formulations since their inherent toxicity is low. At a higher concentration (20,000 ppm) PBO was the most toxic synergist which could be contributing to the toxicity of insecticide when used in formulations