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

Abstract

Larvae of the winter moth Operophteru brurnutu 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 O 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, revent a total decline in RGR, both, the maximum larval weight and the weight of freshly emerged Emales 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 0. brurnutu development.

Reproductive capacity of the horse chestnut scale insect, Pulvinaria regalis Canard (Hom., Coccidae)

“…The linear relationship between adult female size and fecundity in insects has been reported on many occasions for the Hemiptera and other insects (e.g. WAY 1968;LEATHER and WELLINGS 1981;DIXON 1985). The existence of a curvilinear association which better describes the data has not been demonstrated so often.…”

“…Some insects within the Hemiptera, such as certain aphids, tend to have the maximum potential number of offspring predetermined early in life based on a specific and constant ovariole number (LEATHER and WELLINGS 1981); this would dictate a maximum theoretical fecundity which in turn necessitates an upper asymptote to the size/fecundity relationship. The ability to realise this potential is likely to be a function of resources available to the female during growth, via an increase in embryos per ovariole (LEATHER and WELLINGS 1981). Thus, a very small female, whilst able to survive, might only be able to provide minimal requirements for egg production until a certain body size is reached.…”

Effects of elevated temperature on multi‐species interactions: the case of Pedunculate Oak, Winter Moth and Tits

“…Dewar & Watt (1992) predicted that climatic warming would result in decreased synchrony with budburst in Sitka Spruce ( Picea sitchensis ) and Kerslake & Hartley (1997) suggested that synchronization with Heather ( Calluna vulgaris ) is unimportant. If egg hatch occurs before or after Oak budburst, the caterpillars can disperse to other hosts (Smith 1972; Kirsten & Topp 1991), but there is little understorey in Wytham, or other mature woodlands, for them to feed on. In any case, Oak is considered to be the optimum host for Winter Moth (Wint 1983) and, because dispersal must be dangerous, it is probably a last resort.…”

Relative susceptibility of Salix clones to chrysomelid beetles: evidence from the Stott willow collection at Ness

“…Arnongst these physical factors leaf size, leaf toughness and the presence of trichomes all influence palatability to insects (WARING and PRICE 1988;BoGATKO 1990;BoGAGHEVA 1994;MATSUKI and MAGLEAN 1994). The nutritive value of a leaf to a developing insect, particularly the available soluble nitrogen concentration, varies throughout the growing season (THOMAS and HODKINSON 1991;KiRSTEN and ToPP 1991), with food quality declining as the leaf ages (IVlEYER and MONTGOMERY 1987). The nutritive value of a leaf to a developing insect, particularly the available soluble nitrogen concentration, varies throughout the growing season (THOMAS and HODKINSON 1991;KiRSTEN and ToPP 1991), with food quality declining as the leaf ages (IVlEYER and MONTGOMERY 1987).…”

“…Cheniical effects are more subtle, with sornetimes a close inter-relationship apparent between the concetitrations of nutritive and defensive chemicals within the leaves (LARSSON et al 1986). The nutritive value of a leaf to a developing insect, particularly the available soluble nitrogen concentration, varies throughout the growing season (THOMAS and HODKINSON 1991;KiRSTEN and ToPP 1991), with food quality declining as the leaf ages (IVlEYER and MONTGOMERY 1987). Beyond the point of senescence, however, soluble nutrients are again mobilized and food quality may tmprove for some insects.…”