Resistance and cross-resistance to neonicotinoid insecticides and spinosad in the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae)

The Colorado potato beetle, Leptinotarsa decemlineata (Say), has developed resistance to many insecticides used for its control, recently including imidacloprid, a neonicotinoid compound. Other neonicotinoids are now being deployed to control this pest. A key point in the strategies of resistance management is the monitoring of resistance and cross-resistance. In the summer of 2003, imidacloprid-resistant adult Colorado potato beetles collected from Long Island, New York, USA were bioassayed using topical applications of imidacloprid and nine other neonicotinoids. Compared to a standard susceptible strain, the Long Island beetles showed 309-fold resistance to imidacloprid, and lower levels of cross-resistance to all other neonicotinoids, despite these never having been used in the field, i.e., 59-fold to dinotefuran, 33-fold to clothianidin, 29-fold to acetamiprid, 28-fold to N-methylimidacloprid, 25-fold to thiacloprid, 15-fold to thiamethoxam, 10-fold to nitenpyram, but less than 2-fold to nicotine. In injection bioassays, high resistance to imidacloprid was also found (116-fold). Piperonyl butoxide partially suppressed resistance to imidacloprid, but the resistance level was still over 100-fold, indicating that other mechanisms were primarily responsible for resistance. Low levels of resistance (8- to 10-fold) were found to the nicotinic activator, spinosad, in an imidacloprid-resistant strain collected from the same field in 2004. The cross-resistance seen with all the neonicotinoids tested suggests that the rotation of imidacloprid with other neonicotinoids may not be an effective long-term resistance management strategy. Rotation with spinosad also carries some risk, but it is unlikely that spinosad resistance in this case is mechanistically related to that for the neonicotinoids.     

Effectiveness of two insect growth regulators against Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) and Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) and their impact on population densities of arthropod predators in cotton in Pakistan

Field efficacies of two insect growth regulators (IGRs) at two recommended application rates, buprofezin at 370 and 555 g AI ha(-1) and lufenuron at 37 and 49 g AI ha(-1), were determined against the sweet potato whitefly, Bemisia tabaci (Gennadius), and the cotton bollworm, Helicoverpa armigera (Hübner), in experimental plots of cotton at the Directorate of Cotton Research, Faisalabad, Pakistan. Adverse effects of the IGRs on populations of associated arthropod predators, namely geocorids, chrysopids, coccinellids, formicids and arachnids, were also assessed. Both IGRs significantly reduced populations of B. tabaci at each application rate 24, 48 and 72 h after treatment, and higher doses were more effective than lower doses. Buprofezin was not effective against H. armigera at any tested dose for any time of treatment in any spray. Lufenuron applied at 37 and 49 g AI ha(-1) effectively suppressed H. armigera populations, resulting in significant reductions in crop damage. At lower doses, both IGRs appeared safe to predator populations, which did not differ significantly in IGR-treated versus untreated control plots. Population densities of formicids and coccinellids were significantly lower at high concentrations of both IGRs in treatment plots, possibly as a result of reduced prey availability. The potential role of buprofezin and lufenuron for control of B. tabaci and H. armigera in a spray programme and the likelihood of direct toxic effects of IGRs on predatory fauna of cotton are discussed.     

Effects of pH on chemical stability and de-esterification of fenoxaprop-ethyl by purified enzymes, bacterial extracts, and soils

De-esterification is an initial step in the metabolism of certain herbicides, for example, fenoxaprop-ethyl [(+/-)-ethyl 2-[4-[(6-chloro-2-benzoxaolyl)oxy]phenoxy]propanoate] (FE). The ethyl-ester bond cleavage of FE to fenoxaprop acid (FA) by purified enzymes, crude bacterial enzyme preparations, and soils was investigated. In similar experiments fluorescein diacetate (FDA) was used as an alternative substrate. FE stability was pH sensitive in acidic buffered solutions; that is, below pH 4.6, rapid nonenzymatic hydrolysis of the benzoxazolyl-oxy-phenoxy ether linkage occurred, forming 6-chloro-2,3-dihydro-benzoxazol-2-one (CDHB) and ethyl 4-hydroxyphenoxypropanoate or 4-hydroxyphenoxypropanoate. With porcine esterase and cell-free Pseudomonas fluorescens extracts, activity on FE and FDA was most rapid at pH 7.6-8.6 but decreased 80-90% at pH 5.6. Yeast (Candida cylindrica) lipase-mediated de-esterification of FE and FDA was not as sensitive to pH; that is, activity at pH 4.6 was 70% of that at pH 7.6. Short-term incubations (20 h) were conducted in eight soils (pH 4.5-6.9) treated with (14)C-chlorophenyl ring-labeled FE (2 mg kg(-)(1)). In the most acidic soils (pH 4.4-4.5) 25% of the (14)C was recovered as FA, versus 30-40% in moderately acid soils (pH 5.0-5.6) and 55% in neutral soils (pH 6.8-6.9). There was a similar correlation between soil pH and FDA de-esterification. CDHB was formed in all acidic soils with levels 4-fold greater in pH 4.4-4.5 soils than in pH 5. 0-5.6 soils. CDHB was not formed in neutral soils. Results demonstrate some chemical hydrolysis (benzoxazolyl-oxy-phenoxy ether linkage) of FE in acid soils, the sensitivity of enzymatic de-esterification of FE to pH, and the potential of FDA as a colorimetric indicator for esterase hydrolysis of FE.     

Widespread parallel evolution in sticklebacks by repeated fixation of Ectodysplasin alleles

Major phenotypic changes evolve in parallel in nature by molecular mechanisms that are largely unknown. Here, we use positional cloning methods to identify the major chromosome locus controlling armor plate patterning in wild threespine sticklebacks. Mapping, sequencing, and transgenic studies show that the Ectodysplasin (EDA) signaling pathway plays a key role in evolutionary change in natural populations and that parallel evolution of stickleback low-plated phenotypes at most freshwater locations around the world has occurred by repeated selection of Eda alleles derived from an ancestral low-plated haplotype that first appeared more than two million years ago. Members of this clade of low-plated alleles are present at low frequencies in marine fish, which suggests that standing genetic variation can provide a molecular basis for rapid, parallel evolution of dramatic phenotypic change in nature.