Potential use of Clerodendrum capitatum extracts and its formulation for control of three major stored product beetles

Abstract

Objective: Insecticidal activity of Clerodendrum capitatum extracts against the stored product insect pest, Sitophilus oryzae (L.), Rhyzopertha Dominica (F.), and Tribolium castaneum (Herbst) were investigated. Materials and Methods: Hundred grams of C. capitatum powder was sequentially extracted with a series of solvents of increasing polarity in a Soxhlet apparatus and the extracts were concentrated on rotary evaporator to make it solvent free and the residue dissolved in a known volume of methanol and the solution was assayed for insecticidal activity by the fumigant toxicity. Hexane extract which showed maximum activity was selected for the preparation of herbal formulation and for its insecticidal properties and phytotoxicity. The herbal formulation obtained from leaves of C. capitatum was investigated by GCMS and GC/FID. Results: Clerodendrum capitatum ethyl extract had a very strong repellent activity to adults of all three major stored grain insects and was significantly repellent at a 1.58 mg/cm2. The hexane extract (oil) had high fumigant activity with LC50 values in the range between 25 and 32 μg/L. A total of 14 components representing 97.8% of the formulation were identified and the main compounds in the formulation were found to be 2-Heptanone, 3-methyl (33.9 %) and Hexahydrofarnesyl acetone (25.3%) followed by 3-Dodecen-1-al (10.2%) and 8-Methyl-1-undecene (4.9%). Further, herbal formulation was found to be highly toxic to mixed age cultures of all three major stored grain insect pests which recorded 80%-90% mortality at dose of 200 μg/L in 24 h exposure, where as 100% mortality achieved at dose of 200 μg/L in 72 h exposure, respectively. Conclusion: The results indicate that extracts and formulation of C. capitatum has the potential to be developed in to a natural insecticide or repellent for controlling of stored product beetles.