Baseline studies and preliminary resistance survey of Australian populations of cotton aphid Aphis gossypii Glover (Hemiptera: Aphididae)

Abstract

Cotton aphids, Aphis gossypii, may be more troublesome in transgenic (Ingard®) cotton, because an overall reduction in pesticide use in transgenic cotton for the control of pests such as Helicoverpa spp., gives reduced control of concurrent aphids. Additionally, coincidental cotton aphid in conventional cotton is being exposed to an increasing number of organophosphate insecticides targeted against Helicoverpa spp. Resultant insecticide sprays targeted specifically at cotton aphid, are likely to increase and must be managed to maintain insecticide susceptibility. As a first step to studying resistance in cotton aphid, two strains were collected from unsprayed sources and tested against 21 registered or experimental insecticides by laboratory bioassay, to establish baseline data for resistance monitoring. The LC99.9 of the more susceptible strain was used arbitrarily as a discriminating concentration to detect resistance in three populations of cotton aphid collected in cotton growing districts of New South Wales. In contrast to overseas studies, our results suggest that Australian cotton aphid was resistant to endosulfan and pyrethroids but not to carbamates or organophosphates.

Detection of <i>kdr</i> pyrethroid resistance in the cotton aphid, <i>Aphis gossypii</i> (Hemiptera: Aphididae), using a PCR-RFLP assay

“…is treatment applied a uniform deposit (1.6±0.007 mg cm −2 ) of insecticide onto the petri dish. Aphids were sprayed at a rate of 0.003 g/L, a rate tenfold higher than the discriminating dose (DD) (a dose that will kill 99.9% of our reference susceptible population) calculated for lambda-cyhalothrin 3) to ensure survivors displayed a resistant phenotype and remove the possibility of false-positive resistant aphids being selected for subsequent testing. 19) A er spraying, each Petri dish was wrapped with plastic cling lm in which tiny perforations were made to prevent condensation.…”

“…e complete bioassay procedure has been described previously. 3) 2. DNA extraction DNA was extracted from discriminating dose survivors of the bioassay procedure as well as from eight individuals of a reference-susceptible strain, SB, which was also held at EMAI, Camden.…”

“…As the dose set to spray the aphids was tenfold above the LC 99.9 level routinely used in bioassay procedures 3) (to ensure survivors displayed a resistant phenotype), this strongly suggested high-level pyrethroid resistance to the insecticide used. e 11 survivors were extracted and subsequently used for PCR.…”

“…2) Transgenic cotton was implemented in Australia in 1996 to control Helicoverpa spp., and since then insecticide use has been dramatically reduced. 3) is reduction typically occurs during the rst half of the cotton season, 3,4) allowing resurgence of sucking pest populations, such as A. gossypii, to occur. 5) In China, largescale outbreaks of A. gossypii populations in transgenic cotton crops have weakened bene ts associated with its cultivation.…”

“…In Australia, SPs are currently not recommended for the control of A. gossypii in cotton, yet resistance against this insecticide group by A. gossypii on cotton has been detected. 3) In China, a greater than 1,000-fold resistance to the pyrethroid deltamethrin was reported, 7) and in Pakistan, resistance ratios generally above 1,000-fold were seen in response to seven di erent pyrethroids. 8) Additionally, resistance has been detected in the United States.…”