Toxicity Tests of Some Insecticides against Fruit Flies II Dacus cucurbitae Coquillet and Dacus tau (Walker)

Abstract

Dacus tau (Walker) is found as common as Dacus cucurbitae Coquillet to attack many vegetable fruits such as sponge gourds, pumpkin, cucumber, water melon, throughout the country. The appearance and damage of D.tau so closely resemble to D. cucurbitae that most of the destruction has been blamed to the latter and very little is known about the control of the former. Comparative toxicity laboratory tests were made to the two species in order to find insecticides which are effective for the simultaneous control of these fruit flies. Dimethoate, fenvalerate, malathion, naled, and trichlorfon were applied in baits and tested against 1, 7, 14, 21, and 28 days old adult flies using the feeding method. In the case of D. cucurbitae, susceptibility to malathion and fenvalerate was increased as the age of flies increased. Fourteen days old flies showed the most tolerant age to dimethoate, naled, and trichlorfon. On the other hand, most resistant age of D.tau to all tested insecticides was found at seven days old. D. cucurbitae, in general, showed higher resistant to the tested insecticides than D. tau. The susceptibility to insecticides of the two species was ranged from high to low as follows : dimethoate, naled, trichlorfon, malathion, and fenvalerate respectively for D. cucurbitae, and dimethoate, trichlorfon, naled, malathion, and fenvalerate respectively for D. tau. When ten insecticides were applied by the topical drop method on three days old flies, D. cucurbitae showed higher resistant than D. tau to cypermethrin, fenvalerate, malathion, and trichlorfon. On the contrary, higher susceptibility of the former species to cabaryl, decamethion, dimethoate, oxydemeton-methyl, permethrin, and vamidothion was also observed. The susceptibility of both species to the test insecticides was ranged from high to low as follows ; oxydemeton-methyl, fenvalerate, dimethoate, permethrin, decamethion, cypermethrin, trichlorfon, malathion, vamidothion, and cabaryl respectively for D. cucurbitae, and trichlorfon, malathion, fenvalerate, oxydemeton-methyl, dimethoate, cypermethrin, decamethion, permethrin, vamidothion, and cabaryl respectively for D. tau.