Influence of Oilseed Rape Seed Treatment with Imidacloprid on Survival, Feeding Behavior, and Detoxifying Enzymes of Mustard Aphid, Lipaphis erysimi

Abstract

Imidacloprid application, as a seed coating agent on oilseed rape, is recommended to control mustard aphid, Lipaphis erysimi (Kaltenbach) (Hemiptera: Aphididae). In this study, responses of L. erysimi were investigated, including survival, feeding behavior, and detoxifying enzymes, on the oilseed rape seedlings grown from seeds coated with imidacloprid at rates of 6, 12, or 18 g active ingredient (a.i.)/kg seed. The results showed that the aphids' survival rate, together with that of the progeny of the survivors, on the seed-treated seedlings significantly decreased. This indicates that the aphid population in fields can be suppressed effectively. The electrical penetration graph (EPG) technique was used to record aphid feeding behaviors on two-, four-, and six-leaf stages of oilseed rape seedlings that had been seed-coated with imidacloprid, and individual responses were revealed during the aphid feeding behavior. On the plants at the two-leaf stage, aphid feeding behaviors were influenced, showing decreased frequency of stylet penetration into the leaf (probe) or into the mesophyll cells (potential drops, pds for short), and shortened duration of stylet event in the leaf (probe) or in the phloem. On the plants at the four- and six-leaf stages, these impacts of imidacloprid were weakened; however, the saliva secretion duration in phloem was shortened to less than 5 min in all imidacloprid treatments. The activity of mixed-function oxidase in aphids maintained on the treated seedlings with imidacloprid was elevated. In conclusion, imidacloprid could be used as a seed coating agent for aphid control, but chemical resistance in aphids should not be ignored.

Keywords: Lipaphis erysimi; coating agent; feeding behavior; imidacloprid; oilseed rape.

Figure 1

Effect of imidacloprid seed treatments on (a) aphids’ and (b) their offspring’s survival rate. CN: Control; L: Seed coated by low imidacloprid dose; M: Seed coated by medium imidacloprid; H: Seed coated by high imidacloprid dose. Bars indicate standard errors. Bars with the same letters are homogeneous groups or are not statistically different. v. = value.

Figure 2

Survival of (a) tested aphids and (b) their progeny on oilseed rape seedlings that had been seed treated with imidacloprid. CN: Controls; L: Seed coated with low imidacloprid dose; M: Seed coated by medium imidacloprid dose; H: Seed coated by high imidacloprid dose. Bars indicate standard errors. Data were analyzed using analysis of variance (ANOVA) followed by Tukey’s test, and different lower-case letters indicate significant differences (p < 0.05).

Figure 3

Effect of imidacloprid seed treatments on aphids’ detoxifying enzymes (average ± standard error), (a) carboxylesterase, (b) glutathione-s-transferase, and (c) mixed-function oxidase. CN: The controls; L: Seed coated by imidacloprid of low dose; M: Seed coated by imidacloprid of median dose. Different small letters show significant difference (p < 0.05).