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The cabbage maggot, Delia radicum L., has a bimodal pattern of emergence caused by the presence in populations of early and late-emerging genotypes that differ in their pupal development time. These genotypes could also express different egg-laying strategies. To examine oviposition patterns between genotypes and, particularly, their response to temperature, the egg-laying activity of females and egg mortality from each genotype were evaluated at temperatures from 12 to 30°C. Several criteria were used to describe the oviposition pattern: longevity of females, preoviposition period, lifetime fecundity, number of oviposition bouts, duration and number of eggs for each oviposition bout, duration of an oviposition cycle, and time interval between oviposition bouts. All criteria were similar between genotypes, except the preoviposition period and time interval between oviposition bouts. The preoviposition period was 1-4 d longer for the early emerging genotype than for the late-emerging genotype at temperatures <25°C, but similar at temperatures ≥25°C. The time interval between oviposition bouts of early emerging genotype was a few hours longer than for the late-emerging genotype at all temperatures. All oviposition pattern criteria responded to temperature, except the duration of oviposition bouts (≈6.5 d) and egg mortality (≈11%). The duration of a bout could be a compromise between oogenesis duration and the risks associated with egg deposition. According to these results, early and late-emerging genotypes express similar egg-laying strategies for all temperatures tested. [ABSTRACT FROM AUTHOR]

This study investigated the effects of partial plant resistance on the lettuce aphid Nasonovia ribisnigri (Mosley) (Hemiptera: Aphididae), a major pest of cultivated lettuce (Lactuca sativa L.), and one of its parasitoids, Aphidius ervi Haliday (Hymenoptera: Braconidae). Aphids were reared on susceptible (L. sativa variety Estival; S) or partially resistant (Lactuca serriola L. PI 491093; PR) lettuce, and next parasitized by A. ervi females. Fitness proxies were measured for both aphids and parasitoids. Developmental time to adult stage took longer for alate and apterous aphids (an average of 3.5 and 1.5 additional days, respectively) on PR than on S lettuce, and fecundity of alate aphids reared on PR lettuce was reduced by 37.8% relative to those reared on S lettuce. Size (tibia length) and weight of aphids reared on PR lettuce were lower than for aphids reared on S lettuce from the third and second instar onward, respectively. Parasitism of aphids reared on PR plants resulted in lower parasitoid offspring emergence (-49.9%), lower adult female (-30.3%) and male (-27.5%) weight, smaller adult female (-17.5%) and male (-11.9%) size, and lower female fecundity (37.8% fewer eggs) than when parasitoids developed from aphids reared on S plants. Our results demonstrate that partial aphid resistance in lettuce negatively affects both the second and third trophic levels. Host plant resistance in cultivated lettuce may therefore create an ecological sink for aphid parasitoids.

The seasonal development of the swede midge Contarinia nasturtii Kieffer was studied in Quebec in 2004 and 2005 using pheromone traps, emergence cages, and visual inspection in relation to degree-day accumulations (DD7.2 degrees C). Peak emergence of overwintering adults occurred between 344 and 731 DD7.2 degrees C (second half of June) during both seasons. The swede midge had three to four overlapping generations in Quebec based on adult captures in pheromone traps and abundance of larvae in the field. The level of infestation was higher in late transplants than in early transplants, with cauliflower and broccoli being more susceptible to damage than white or red cabbage under high pest population.