Behavior and performance of gypsy moth in multiple host situations.

Abstract

Because many gypsy moths may experience multiple species diets in nature, I studied performance and behavior of gypsy moths in multiple host situations in Michigan. I examined effects of host switching on insect performance, utilizing diets which were combinations of red and white oaks and bigtooth and trembling aspens. Conclusions include: (1) Insects performed best on a first host of red oak and most poorly on a first host of bigtooth aspen. (2) Insects did not uniformly perform better or worse on multiple species diets than on single species diets. (3) Both first and second host species affect insect performance; some aspects of performance are affected more strongly by the first host and some by the second host. (4) Insects performed best on a second host of trembling aspen. Performance also was investigated in relation to egg hatch/feeding initiation times over a 3 week period. Insects placed on trees earliest had highest mortality, slowest development, and lowest larval weights late in the season, while those placed 3 weeks later had lowest mortality, fastest development, and heaviest larval weights throughout the season. Nutritional indices were examined for fourth and fifth instar gypsy moths fed sequential diets. Combinations were formed from northern pin and white oaks and bigtooth and trembling aspens. Indices were evaluated under field conditions. Conclusions include: (1) Insects eating northern pin oak before the switch performed best after the switch. (2) Insects grew best on a second host of trembling aspen despite mediocre to low food conversion efficiencies; low efficiencies were offset by high consumption rates. (3) Insects did not consume more, grow faster, or use food more efficiently when the second host was either the same species as the rearing plant or closely related to it. Food choices of older gypsy moths in multiple species situations were evaluated by caging larvae on intermingled foliage of host trees. Species pairs tested were northern pin oak/white oak, northern pin oak/bigtooth aspen, white oak/bigtooth aspen, and witch-hazel/bigtooth aspen. Findings include: (1) Early experience on northern pin oak did not uniformly affect later choices of insects. (2) Insects distinguished strongly between congeneric species. (3) Insects strongly avoided white oak. (4) Insects switched between available diet items but frequency of movement was not high.