Trade-offs in the host selection by phloeophagous parasitic insects on conifers

点击翻译按钮获取中文摘要

Insects and plants have co-existed for hundreds of millions of years, often evolving close associations and even co-dependence. The most common interaction between plants and insects involve the utilization of plant tissue as a food and/or breeding resource by insects, often placing insects in direct conflict with human interests. In response to the selective pressures exerted by insects feeding or breeding in wood, most woody plants have evolved a potent cocktail of defensive chemicals. Most species of insects can tolerate only limited exposure to such chemicals, and hence feed and breed only in dead hosts, but a limited number of species can utilize live tissue, either invading it as the host is dying, killing it, or in a few cases living as a parasite. The parasitic insects are of interest in understanding the cues that insects use in selecting a host, something we still don't understand very well. The ability of a host tree to defend itself against attack depends on both its vigour and the defensive chemicals used. If tree vigour is compromised, e.g., during droughts, the defensive ability of the tree will also be diminished, regardless of how well defended the tree is chemically. Since insect larvae cannot leave an unsuitable host, a mistake by their mother will ultimately result in low reproductive fitness. Poorly defended trees tend to get attacked by many different insects, leading to severe competition. Thus, an insect orienting a host must make a cascade of decisions, involving trade-offs between coping with host defense or competition. How these choices are made is the focus of my research program. Research will be conducted on two phloem feeding species that are parasitic on conifers. Using field-centred methods, including harmonic radar to track insects and chemical analyses to determine potential host resistance factors, I will examine what cues the insects use, how they respond to them to make an optimal host choice. The results will provide expanded knowledge of insect-plant interactions, including an understanding of what factors contribute to resistance in conifers.