Sublethal effect of chlorpyriphos and fenpropathrin on functional response of Habrobracon hebetor (Hym.: Braconidae)

Abstract

One of the criteria for selecting a suitable natural enemy is its functional response to different densities of the host. Habrobracon hebetor (Say) is a larval ectoparasitoid of several species of lepidopteran. Functional response of H. hebetor, after treatment with LC25 of chlorpyrifos and fenpropathrin in three stages, was assessed to different densities of fifth instar of Ephestia kuehniella (2, 4, 8, 16, 32 and 64). LC25 values were estimated to be 0.043, 5.36 and 2.00 and 0.38, 13.9 and 4.45 mg a.i. l−1 for the larval, pupal and adult stages for chlorpyrifos and fenpropathrin, respectively. Host densities were offered to treated wasps for 24 h. Experiments were replicated 10 times. The results showed that the functional responses of wasps in control as well as immature stages treatments were Type III, whereas those of adult stage were Type II. a (Type II) or b (Type III) and Th parameters were evaluated with Roger’s equation. b and Th in control were assessed to be 0.0129 and 0.1723 h, respectively. These parameters were estimated in chlorpyrifos and fenpropathrin to be 0.0052, 0.00718 and 0.1945, 0.2492 h in larval stage; 0.00817, 0.00916 and 0.2736, 0.3108 h in pupal stage; and a and Th were 0.0064, 0.0137 h−1 and 0.2492, 0.2242 h in the adult stage, respectively. The insecticide had no significant effect on the searching efficiency of H. hebetor compared with those treated in control; however, they had significant effect on the handling time of the parasitoid and increased it, except in the larval stage treated with chlorpyrifos treatment.