Feder Jeffrey L, Reynolds Katherine, Go Wesley, Wang Emma C
Department of Biological Sciences, University of Notre Dame, 46556, Notre Dame, IN, USA.
Department of Biology, California State University at Hayward, 94542, Hayward, CA, USA.
Oecologia. 1995 Apr;101(4):416-425. doi: 10.1007/BF00329420.
Intra- and interspecific resource competition are potentially important factors affecting host plant use by phytophagous insects. In particular, escape from competitors could mediate a successful host shift by compensating for decreased feeding performance on a new plant. Here, we examine the question of host plant-dependent competition for apple (Malus pumila)- and hawthorn (Crataegus mollis)-infesting larvae of the apple maggot fly, Rhagoletis pomonella (Diptera: Tephritidae) at a field site near Grant, Michigan, USA. Interspecific competition from tortricid (Cydia pomonella, Grapholita prunivora, and Grapholita packardi) and agonoxenid (subfamily Blastodacninae) caterpillars and a curculionid weevil (Conotrachelus crataegi) was much stronger for R. pomonella larvae infesting the ancestral host hawthorn than the derived host apple. Egg to pupal survivorship was estimated as 52.8% for fly larvae infesting hawthorn fruit without caterpillars and weevils compared to only 27.3% for larvae in harthorns with interspecific insects. Survivorship was essentially the same between fly larvae infesting apples in the presence (44.8%) or absence (42.6%) of interspecific insects. Intraspecific competition among maggots was also stronger in hawthorns than apples. The order or time that a larva exited a hawthorn fruit was a significant determinant of its pupal mass, with earlier emerging larvae being heavier than later emerging larvae. This was not the case for larvae in apples, as the order or time that a larva exited an apple fruit had relatively little influence on its pupal mass. Our findings suggest that decreased performance related to host plant chemistry/nutrition may restrict host range expansion and race formation in R. pomonella to those plants where biotic/ecological factors (i.e. escape from competitors and parasitoids) adequately balance the survivorship equation. This balance permits stable fly populations to persist on novel plants, setting the stage for the evolution of host specialization under certain mitigating conditions (e.g. when mating is host specific and host-associated fitness trade-offs exist).
种内和种间资源竞争是影响植食性昆虫寄主植物利用的潜在重要因素。特别是，逃离竞争者可以通过补偿在新植物上降低的取食性能来介导成功的寄主转移。在这里，我们在美国密歇根州格兰特附近的一个田间地点，研究了苹果实蝇（Rhagoletis pomonella，双翅目：实蝇科）以苹果（Malus pumila）和山楂（Crataegus mollis）为食的幼虫对寄主植物的依赖性竞争问题。来自卷蛾科（苹果蠹蛾Cydia pomonella、李小食心虫Grapholita prunivora和Packard小食心虫Grapholita packardi）和织蛾科（Blastodacninae亚科）毛虫以及象甲科象鼻虫（山楂象甲Conotrachelus crataegi）的种间竞争，对于侵染原始寄主山楂的苹果实蝇幼虫来说，比对衍生寄主苹果的竞争要强得多。对于侵染没有毛虫和象鼻虫的山楂果实的实蝇幼虫，卵到蛹的存活率估计为52.8%，而对于有物种间昆虫的山楂果实中的幼虫，存活率仅为27.3%。在有（44.8%）或没有（42.6%）物种间昆虫的情况下，侵染苹果的实蝇幼虫的存活率基本相同。山楂中蛆虫的种内竞争也比苹果中更强。幼虫离开山楂果实的顺序或时间是其蛹重的一个重要决定因素，较早出现的幼虫比晚出现的幼虫更重。苹果中的幼虫情况并非如此，因为幼虫离开苹果果实的顺序或时间对其蛹重的影响相对较小。我们的研究结果表明，与寄主植物化学/营养相关的性能下降可能会将苹果实蝇的寄主范围扩展和种群形成限制在那些生物/生态因素（即逃离竞争者和寄生蜂）能够充分平衡存活方程的植物上。这种平衡使得稳定的实蝇种群能够在新植物上持续存在，为在某些缓解条件下（例如当交配是寄主特异性的且存在寄主相关的适合度权衡时）寄主专一化的进化奠定了基础。
