Acceptance of willow‐species for the development of the winter moth, Operophtera hrumata (Lep., Geometridae)

Larvae of the winter moth Operophtera hrumata were fed on a variety of willow species which had bud burst up to 4 weeks prior to the oak bud burst. The larvae were analyzed for growth, feeding efficiency and nitrogen budgets as a function of host plant, nutrient content and temperature. Furthermore, the reproductive success of females was tested according to the host plants used as food during their larval stage. Within the temperature range from 5 ° to 20 °C consumption rate (RCR) and growth rate (RGR) of larvae increased but the overall efficiency of conversion of ingested food (ECI) was unaffected. Using an alternating regime with daily temperatures fluctuating by 10°C over a period of 12 h, each RGR and the maximum larval weight were the same as found at the mean constant temperature. An alternating regime, however, did increase the RCR of larvae. Feeding performance of larvae was also affected by the host plants. Food consumption increased with decreasing plant quality. Although the increase in RCR did not, however, prevent a total decline in RGR, both, the maximum larval weight and the weight of freshly emerged females were similar between the various trials conducted. The results indicate that the consumption and utilization of food are dynamic processes and that caterpillars in early spring exhibit compensatory responses to changes in temperature as well as to the host plant. An analysis of both the nutrient content (nitrogen and water) of the willow species and of the caterpillar utilization indices upon each host plant did not show any consistent trends. If larvae fed later in the season rather than in the early spring, such compensatory responses were not found. Instead, a decline in RGR, feeding time and/or RCR occurred resulting in a lowering of the maximum weight of larvae hatching at a later time. The mean weight of females according to the different willow species upon which the larvae had fed, did not differ from the mean weight of females originating from oak trees; nor are there differences in fecundity. Hence, winter moth caterpillars may find adequate host plants in early spring before oak bud burst occurs. At the time of oak leaf flush, however, the quality of foliage of at least some willow species may already be suboptimal for O. hrumata development.