Facultative diapause is a strategy that allows insects to initiate an additional generation when conditions are favorable, or to enter diapause when they are not. The occurrence of additional generations within one year can have a profound effect on the ecology and evolution of a species. Most previous studies of the cues that induce facultative diapause in insects have concentrated on photoperiod and temperature. In contrast, we studied the effects of host-plant quality on the induction of larval diapause and subsequent voltinism in a polyphagous insect herbivore, Choristoneura rosaceana (Lepidoptera: Tortricidae). Field experiments demonstrated that the proportion of larvae entering diapause differed among four host-plant species. Larvae feeding on chokecherry were more likely to continue development and produce a second generation than larvae feeding on red maple or black ash. Paper birch was intermediate in diapause induction. Laboratory experiments with excised foliage supported the results of the field experiments and demonstrated that the induction of diapause depended on host species under constant conditions of photoperiod and temperature. A further study with low-and high-quality artificial diet demonstrated that the nutritional quality of larval diet has a direct effect on diapause induction: lowquality diet favored diapause induction. Dispersal of neonate larvae from host foliage did not necessarily reflect host quality and the potential for bivoltinism. We argue that the effect of plant quality on diapause induction in natural populations of insect herbivores merits more attention.

2003. The effect of food supplementation on reproductive success in bumblebee field colonies. -Oikos 103: 688-694.Food availability is a major component of habitat quality. For bumblebee field colonies, it is unknown to what extent reproductive success is limited by food availability relative to other factors such as parasites. To assess the importance of food availability, we carried out a field experiment in the Quebec City area, Canada, in 1999 and 2000, using 45 colonies of Bombus impatiens and B. ternarius. Colonies whose nectar and pollen supplies were increased regularly throughout the season reached larger sizes (in number of workers) and had a higher reproductive success than controls, by 51% and 86% respectively. In particular, food supplementation increased the number of males produced and the probability of producing gynes (young queens). The sex ratio was highly skewed in favour of males overall, and the relative proportion of gynes increased with food supplementation in B. ternarius, but not in B. impatiens. These results suggest that colonies ensure reproduction by producing some males and, given the opportunity (sufficient food availability), will produce gynes. Possible reasons for the increased success of food supplemented colonies are explored. However, despite some clear advantages of having larger food supplies such as the build-up of larger worker populations, food supplementation did not appear to help colonies defend themselves against macroparasites because experimental and control colonies experienced similar levels of parasitism by Psithyrus, Fannia canicularis, Brachicoma de6ia and Vitula edmandsae.

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Adults of many species of Lepidoptera, principally the males, frequent mud puddles, edges of streams, carrion and animal excreta where they imbibe moisture, an activity referred to as 'puddling'. Sodium ions are the only known stimulus present which cause males of at least two lepidopteran species to drink for extended periods. In the European skipper Thymelicus lineola (Ochsenheimer) (Lepidoptera: Hesperiidae), only males puddle, even though they have concentrations of abdominal sodium 2-3 times that of females at emergence. During their first mating, males transfer 32% of their abdominal sodium to females. This could be of considerable importance given that an average egg complement contains >SO% of the total body sodium of females at emergence. Virgin females. as well as having reduced fecundity, have reduced longevity. This is attributed to virgins not obtaining important nutrients which males transfer to females during mating. Access to sodium ions increases the total number of matings by c . 50% for males living >1S days. Access to sodium ions by once-mated males increases the percentage of males which re-mate on the day following first mating; the percentage of females, mated to the twice-mated males, which lay >SO% fertile eggs; and the drought resistance of eggs laid by those females.