Influence of varietal differences and pyrethroid insecticides on the population densities of cucumber insect pests, Dacus spp. and Bactrocera invadens (Diptera: Tephritidae), and fruit damage

Abstract

Two insecticidal trials were carried out between 2004 and 2008 at the Teaching and Research Farm, Federal University of Agriculture, Abeokuta, Nigeria. In the first experiment, the pyrethroid insecticides - deltamethrin, lambda-cyhalothrin and cypermethrin were evaluated for ejfcacy against the cucumber fruit flies, Bactrocera invadens and Dacus spp, and cost benefit. In the second trial, the influence of varietal differences on the efficacy of lambda-cyhalothrin (which was selected as the most effective pyrethroid from the first trial) was investigated using four cucumber varieties. From the insecticide screening experiment, numbers of exit holes and fruit fly larvae recorded from infested fruits were significantly lower (P < 0. 05) in treated plots, while yield was higher in treated plots than control. The three pyrethroids tested were effective against the fruit flies, but deltamethrin gave the highest economic returns. In the second trial, number of fruit fly larvae and damage recorded were significantly higher on Hybrid F, compared to other varieties. The highest damage (P < 0.05) (74.6 %) and number of exit holes (80.4%) was found on Hybrid F, which was therefore, the most preferred by the fruit flies. However, while lambda-cyhalothrin was effective in reducing fruit fly damage, the significant interaction that existed between lambda-cyhalothrin and cucumber variety suggest that fruit flies density was jointly influenced by the two factors, and that reduction in fruit fly population by the insecticide depends on the cucumber variety used.