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Laboratory experiments were conducted to compare relative Þtness of strains of Colorado potato beetle resistant and susceptible to Bacillus thuringiensis subsp. tenebrionis Cry3A toxin. Net replacement rates and intrinsic rates of population increase were calculated for resistant and susceptible populations. During the experiment, susceptible males on average copulated 13.3 Ϯ 1.5 times, whereas resistant males copulated only 8.0 Ϯ 1.0 times. Susceptible females produced an average of 824.2 Ϯ 68.1 eggs and 590.9 Ϯ 58.5 larvae, which was signiÞcantly Ͼ484.6 Ϯ 48.0 eggs and 334.9 Ϯ 39.7 larvae produced by an average resistant female. As a result, both net replacement rate and intrinsic rate of increase were reduced for the resistant population. Furthermore, twice as many susceptible beetles as resistant beetles survived overwintering diapause. Our results clearly indicate that relative Þtness of resistant individuals is reduced in the absence of B. thuringiensis in the environment. Therefore, relaxation of selection pressure through refugia and insecticide rotation will favor decrease in the frequency of resistant alleles in beetle populations.

The recent introduction of the concept of refuge areas for the management of the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera : Chrysomelidae), on resistant potato highlighted the existence of important gaps in our knowledge and understanding of this pest's movement within and between habitats. The objective of this review is to synthesize the information available for the benefit of crop managers and to identify subject areas in need of additional research. A traditional, somewhat encyclopedic, review of the old and recent literature on research methods, basics of flight and walking, as well as abiotic and biotic conditions for dispersal, revealed a considerable volume of information accumulated since the early 1900s. There is a consensus on the role of abiotic factors on flight and walking, but a better understanding of the biotic factors will be required before the variability of the dispersal response can be fully explained or predicted. Cybernetic models of orientation proposed in the literature were pulled together into a schematic representation of the orientation process in walking L. decemlineata. The model begins the integration of the different conditions and underlying suggested mechanisms responsible for the orientation of the walking beetle. There is remarkably little information on the orientation of potato beetles during flight. Finally, the seasonality of walking and flight dispersal is reviewed in relation to the host habitat and overwintering sites.

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Feeding responses that influence the effectiveness of a polyphagous endemic coccinellid, Coleomegilla maculata (DeGeer), for biological control of Colorado potato beetle, Leptinotarsa decemlineata (Say), in potato were examined in the laboratory. Consumption rate, functional response, prey preference, and the effect of alternate prey were studied for C. maculata adult females feeding upon eggs of Colorado potato beetle; Myzus persicae (Sulzer) and corn pollen were alternate food sources. C. maculata females continuously supplied with eggs attacked an average of 20.8 eggs per 48 h, and introduction of M. persicae significantly reduced but did not eliminate egg feeding. Females starved for 24 h showed a Type II functional response to egg density when offered 10-70 eggs per 24 h in small cages at 26 ± 2°C. Data fit well to the Holling disk equation, which predicted maximum egg consumption of 31.5 eggs per 24 h. The functional response curve showed suppression of egg feeding at high egg densities when aphids were present as alternate prey, but no effect was evident at low egg densities. There was no change in functional response with corn pollen as the alternate food. When Colorado potato beetle eggs and aphids were available in equal numbers, females did not prefer either prey at low prey densities, but they preferred aphids over eggs at high densities. Eggs were an adequate (but not optimal) diet for larval development and adult oviposition relative to M. persicae or corn pollen. Some implications for ecology and effectiveness of C. maculata for control of Colorado potato beetle in potato are discussed.

Trichogramma ostriniae (Hym: Trichogrammatidae), an egg parasitoid of the European corn borer, Ostrinia nubilalis (Lep: Pyralidae), were released into sweet corn (Zea mays L.) fields to study the effects of weather, plant size and distribution of egg masses on egg parasitism by the wasp. Sentinel European corn borer eggs were stapled onto leaves located in the upper, middle and lower third of sweet corn plants 5 to 35 meters away from the wasp release point in either a radial or grid manner. Weather conditions and plant architecture were monitored during the experiments. Logistic regression was used to analyze the data. The results indicated that percentage of eggs parasitized was negatively related to an increase in leaf area as well as an increase in distance eggs were located from the point of release of wasps. Eggs distributed on plants at different directions from the release point received different levels of parasitism. Eggs that were stapled onto leaves in the upper third of a corn plant received much less parasitism than those on the middle and lower third of the plant. Higher mean temperature adversely affected the level of parasitism during hotter times of the season and conversely, lower temperatures (<17 °C ) reduced the egg parasitism during cooler times of the season. The longer the exposure of eggs to wasps, the higher the level of egg parasitism. However, the levels of egg parasitism for 2 day's exposure were almost the same as that for 3 day's exposure due to the limited longevity and egg‐laying behavior of the wasp. These results suggest that inundative releases of T. ostriniae should be made every two to three days, with multiple release points per hectare. In addition, weather conditions and plant architecture, especially temperature, plant height and leaf area must be taken into consideration to optimize levels of parasitism.

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