Susceptibility of Aphis gossypii (Glover) to Insecticides as Affected by Host Plant Using a Rapid Bioassay

Abstract

Listen

Translate article

The susceptibility of Aphis gossypii (Glover) reared on watermelon or cotton to seven insecticides was determined using a Petri dish bioassay. Baseline susceptibility values to each insecticide for susceptible laboratory A. gossypii colonies varied between host plants, but aphids reared on cotton were generally more tolerant to insecticides than aphids from watermelon. The ratio of relative susceptibility of cotton aphids to melon aphids was as much as 1000 with dimethoate or 415 with bifenthrin, however, no significant differences in susceptibility was observed with chlorpyrifos between aphid populations from the two host plants. Orders of toxicity for the seven insecticides varied between host plant, but on watermelon, the order of toxicity was bifenthrin > oxydemeton-methyl > methomyl > dicrotophos > dimethoate > chlorpyrifos > endosulfan. Because of the wide range of response to insecticide doses observed with bifenthrin on melon aphid and with dimethoate and endosulfan against cotton aphid, use of the Petri dish bioassay method as a discriminating-dose field bioassay for these insecticides may not provide consistent estimations of the resistant nature of field populations. Bioassay data taken at 3 h were generally more consistent and provided a more predictive mortality model than those taken at 2 or 4 h for most insecticides. LC50 values estimated for dimethoate with melon aphids using leaf-spray or leaf residue bioassays differed little from LC50 values estimated with the Petri dish bioassay. Because Petri dish bioassays cost less than half as much as plant-based bioassays, provide comparable results, and require less assay time, this method is more suitable for use in monitoring for insecticide resistance in melon aphid.