Artificial diets for rearing the Colorado potato beetle, <italic>Leptinotarsa decemlineata</italic>

Abstract

Colorado potato beetles have been reared successfully through 12 generations on artificial diets containing either 2.5% potato leaf powder or 2.5% lettuce leaf powder/0.75% potato leaf powder. For all but one of the treatment groups, the mean duration of each of the four larval stages was between 0.8 and 1.5 days longer than the durations exhibited by control beetles that had been fed on potato leaves. Maximum weights of prepupae, newly emerged adults and day 5 - 9 adults were approximately 78, 80 and 82%, respectively, of the weights for comparable stages of control beetles. Mean percent mortality for 1 st instars was two to six times higher for artificial diet-fed CPBs than for leaf-fed beetles. However, since pupal mortality was four times higher for control beetles than for beetles reared on artificial diet, mean percent total mortality (newly hatched through the 9 day old adult) was equivalent for leaf-fed beetles and for later generations of potato and Lettuce+Potato diet-fed CPBs. Hemolymph ecdysteroid levels and fluctuations in mature 4 th instar larvae and prepupae were similar in controls and experimental groups. Number of hatchlings produced per adult pair per day (fertility) was approximately eight times greater in control beetles than in later generations of artificial diet-fed beetles, primarily because fewer egg masses were laid per day, percent hatch was lower and cannibalism of eggs was higher in these latter groups. Interestingly, the mean percent hatch, although only 68% of the control value, was 1.5 times greater for beetles reared on diet containing lettuce-leaf powder, and a small percentage of potato leaf powder, than on diet containing only potato leaf powder. Percent hatch was equal for beetles fed on diet containing only lettuce-leaf powder and those fed on potato leaves. Finally, it is noteworthy that the quality of eggs, as judged by the ability of the wasp parasitoid, Edovum puttleri , to parasitize and develop in the eggs, was similar for eggs produced by control beetles and for those produced by beetles fed on potato and Lettuce+Potato diets. The diets and rearing system described here will be useful for providing beetles on a year-round basis for experiments designed to evaluate the effects of potential insect control agents, to investigate the mechanism(s) by which insects become resistant to control agents and for other applied and fundamental studies related to the control of this serious pest. The use of lettuce leaf powder in place of most of the potato leaf powder is especially advantageous because of the much reduced cost and greater availability of lettuce as compared to potato leaves.