The Colorado potato beetle, Leptinotarsa decemlineata (Say)

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.

Colorado potato beetle, Leptinotarsa decemlineata (Say), adults and larvae collected from Long Island, NY, were 100.8 and 13.2 times more resistant to imidacloprid, respectively, compared with a susceptible strain. This high level of resistance appeared in only the third field season of imidacloprid use. Analysis of probit lines from F1 reciprocal crosses indicated that resistance to imidacloprid in adults was inherited autosomaly as an incompletely recessive factor. The degree of dominance of the resistance was -0.23 and -0.10, respectively, 3 and 7 d after treatment (incompletely recessive). The chi2 analysis of response ratio statistics from F1 x susceptible back crosses compared with a monogenic model suggested that more than one locus is responsible for resistance to imidacloprid. Synergism studies with piperonyl butoxide suggested that mixed-function oxidase mediated detoxification is responsible for the resistance to imidacloprid in adults. Synergism studies with S,S,S-tributyl phosphorotrithioate (DEF) indicated that esterase mediated detoxification may be an additional resistance factor. Mixed-function oxidase mediated detoxification is probably also one of the mechanisms of resistance to imidacloprid in larvae. Because the synergists used did not completely eliminate resistance in the resistant strain, there may be additional mechanisms involved. Refugia and crop rotation decrease the frequency of homozygous resistant genotypes and may be effective resistance management strategies, because of the recessive nature of the resistance.

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The increasing resistance to neonicotinoid insecticides raises concerns for the continued effective management of Colorado potato beetles in potatoes and highlights the need for more rigorous practice of integrated pest management methods.

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The aim of this study was to gather quantitative field and laboratory data on the utilization of deciduous leaves as food by Lepidostoma quercina Ross (Trichoptera: Lepidostamatidae) and estimate the effect of this food processing on the stream ecosystem. Samples were taken monthly in a riffle—pool section of Berry Creek, Benton County, Oregon. Maximum larval density was 382 per m2, instantaneous growth rate was 2.7% per day, instantaneous mortality rate was 1.4% per day, and production was 0.19 g·—2·—1. The life cycle of L. quercina and its period of maximum larval growth correspond closely with the period of maximum availability of its prefered food (alder leaves) in the stream. Consumption and fecal production rates were measured gravimetrically. Rates (mg·—1·—1) increased with temperature, food quantity, and conditioning time of the leaves, and decreased with increased size of the larvae. Mean respiration rates of larvae were higher at 10°C than at 5°, but there was no significant difference in mean rates at 10, 15, or 20°C. Respiration rate decreased with increased size of the larvae. Size—specific respiration rates showed regulation of respiration with respect to temperature for small individuals (present in the field in September and October when temperatures are variable) and little or no regulation by large individuals (present in December and January). Stimulation modeling of larval growth based on laboratory data demonstrated that growth and production of L. quercina in the field may be limited by a lack of high—quality food (alder leaves) in late summer and early fall. Consumption of leaves by the simulated population was estimated as 3.1 g·—2·—1. Lepidostama quercina comprised only a small part of the secondary production in Berry Creek (0.19g·—2·—1, vs. 2.2 g·—2 for simuliids) and processed only a small portion of the allochthonous input to the stream. However, significant quantities of fecal material were produced and it was estimated that these fine particle would be sufficient to support ¼ to ½ of the production of simuliids, the dominant riffle species in Berry Creek.

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