Identification of factors influencing flight performance of field-collected and laboratory-reared, overwintered, and nonoverwintered cactus moths fed with field-collected host plants.

Environmental conditions during egg and larval development may influence the dispersal ability of insect pests, thus requiring seasonal adjustment of control strategies. We studied the longest single flight, total distance flown, and the number of flights initiated by wild Cactoblastis cactorum (Berg) (Lepidoptera: Pyralidae) to determine whether the flight performance of overwintered cactus moths with a prolonged feeding phase during development differs from nonoverwintered cactus moths. Pupae of field-collected and laboratory-reared moths were transported together from the United States to Switzerland, and flight mills were used to characterize the flight capacity of 24- to 48-h-old adults during their most active period of the diel cycle. The lack of seasonal variation in flight performance of those moths that developed under controlled environment but were fed with field-collected Opuntia cacti showed that seasonal changes in host plant quality did not affect flight. This consistent flight performance in the mass-reared laboratory population throughout the year is beneficial for sterile insect technique programs, which aim to limit the dispersal of this pest. For field-collected C. cactorum, the larger overwintered females performed similarly to nonoverwintered females, indicating that longer feeding time at lower temperature increases body size but does not influence female flight capacity. Young mated females had a similar flight capacity to unmated ones, suggesting that gravid females may play an important role in invading new habitats. For males, overwintering increased the proportion of long-distance flyers, suggesting that they are well-adapted to locate the more sparsely dispersed females in the spring.

Diel flight pattern and flight performance of Cactoblastis cactorum (Lepidoptera: Pyralidae) measured on a flight mill: influence of age, gender, mating status, and body size.

Cactoblastis cactorum (Berg) (Lepidoptera: Pyralidae) is an invasive herbivore that poses a serious risk to Opuntia cacti in North America. Knowledge of the flight behavior of the cactus moth is crucial for a better understanding of natural dispersal, and for both monitoring and control. We used computer-linked flight mills to investigate diel flight activity and flight performance in relation to gender, age, mating status, and body size. Maximal flight activity for both mated and unmated moths occurred during twilight, whereas flight activity was low during photophase. The total distance flown and the number of initiated flights within a diel cycle were higher in both unmated and mated females than in males, but the longest single flight was similar in both genders. These findings suggest that pheromone trap captures of males likely indicate the simultaneous presence of females and that mated females might even be in areas where males are not detected yet. Flight performance heterogeneity was large, with a small portion of the population (both males and females) performing long unbroken flights, whereas the majority made short flights. Females had higher pupal and adult body size and shorter longevity than males. A few individuals, particularly young mated females, flying long distances may be important for active spread of a population and the colonization of new habitats. Implications of this study in the control of the cactus moth by using the sterile insect technique are discussed.

Effect of rearing strategy and gamma radiation on field competitiveness of mass-reared codling moths (Lepidoptera: Tortricidae).

We compared the field competitiveness of sterile codling moth, Cydia pomonella (L.), males mass-reared through diapause or standard production protocols and treated with either 150 or 250 Gy of gamma radiation. Evaluations were performed during spring and summer 2003 by using field release-recapture tests. Released males were recaptured using traps baited with synthetic pheromone or with virgin females. In addition, mating tables baited with virgin females were used in the summer to assess the mating competitiveness of the released moths. Field performance of released males was significantly improved by rearing through diapause and by lowering the dose of radiation used to treat the insects. These effects were observed during spring when evening temperatures were relatively cool and in summer when evening temperatures were high. These effects were observed regardless of the sampling method (i.e., capture in pheromone-baited traps, virgin female-baited traps, or in mating tables). There were significant interactions between larval rearing strategy and radiation dose with respect to day of recapture. The effect of rearing strategy on male performance was observed immediately after release, whereas the effect of dose of radiation was usually delayed by 2-3 d. In general, the best treatment for improving codling moth male field performance was a combination of rearing through diapause and using a low dose of radiation (150 Gy). The difference in performance when insects were treated with 150 or 250 Gy was greater when males had been reared using standard (nondiapause) rearing protocols, suggesting that diapause rearing may attenuate some of the negative effects of the higher doses of radiation.