Sublethal Effects of Acetamiprid, Pymetrozine and Flonicamid on the Functional Response of Aphidius matricariae Haliday

It is necessary to investigate side effects of the pesticides on natural enemies of pests for integrated pest management (IPM) programs. Insecticides may impair physiological and behavioral traits of parasitoid wasps. This research was designed to study toxicity of actamiprid, pymetrozine and flonicamid on Aphidius matricariae Haliday (Hym.: Braconidae: Aphidiinae), a parasitoid wasp of Aphis fabae Scopoli (Hemi.: Aphididae). Furthermore, their sublethal effect were evaluated on the functional response of the parasitoid wasp of under laboratory conditions (25±1 0C, 65±5% R.H. and 16:8 (L: D) h).

A residual bioassay method was used to determine the toxicity of the insecticides on A. matricariae. Adult parasitoids were exposed to LC25 of the insecticides and distilled water as control on the glass vials and functional response study was done. After 24 h, randomly selected 6 alive mated females were transferred individually to cylindrical containers containing broad bean seedlings infested by densities of 2, 4, 8, 16, 32 and 64 of the third instar A. fabae nymphs. Each host density had fifteen replications. Aphids were left on the plants until mummification of the parasitized individuals. Functional response type was determined using logistic regression and its parameters were estimated by non-linear regression using SAS program.

The LC50 of values of actamiprid, pymetrozine and flonicamid were 3.07, 740.20 and 133.15 mg a.i./l, respectively. The results showed that acetamiprid was more toxic than pymetrozine and flonicamid to adult stage of A. matricariae. Functional response of the parasitoid on control and the insecticides treatments fitted the type II. Attack rate (a) in control, actamiprid, pymetrozine and flonicamid treatments were estimated 0.0432 ± 0.01, 0.0237 ± 0.003, 0.0414 ± 0.004 and 0.0398 ± 0.01 h-1 and handling time (Th) were 0.5170 ± 0.06, 1.4257 ± 0.13, 0.6133 ± 0.05 and 0.6816 ± 0.07 h, respectively. The attack rate (a) value of A. matricariae exposed to acetamiprid was significantly lower than that of control and other insecticides treatments. The highest value of handling time(Th) was observed in acetamipirid. Although, they were not significantly affected by pymetrozine and flonicamid. Maximum rates of parasitism (T/ Th) in control and mentioned insecticides treatments were estimated 46.42, 16.83, 39.15 and 35.21 aphids, respectively.

According to present results, acetamiprid negatively affected the attack rate (a), handling time (Th) and maximum attack rate (T/Th) of parasitoid compared to the control, pymetrozine and flonicamid treatments. Pymetrozine and flonicamid had lower side effects on A. matricariae in comparison with acetamiprid and they were suitable candidates for controlling of A. fabae in combination with A. matricariae. Although, studying side-effects of the insecticides on the mentioned parasitoid wasp in semi-field and field conditions are needed to obtain more applicable recommendations.