Many organisms possessing a haplodiploid genetic system are known to preferentially allocate maleness and femaleness to individual offspring in response to environmental conditions that differentially confer advantages to either sex. (A haplodiploid species is one in which individuals of one sex--usually males--are produced from unfertilized eggs, while fertilized eggs produce individuals of the opposite sex). For instance, parasitic wasps will most likely oviposit a female (fertilized) egg in a relatively large high quality prey individual since the ovipositing female stands to gain more grandoffspring through the function of large, robust daughters than through the function of large sons. In contrast, the female will probably gain more grandoffspring through the function of small sons than through small daughters and will thus most likely allocate male (unfertilized) eggs to small, low quality, hosts. Differential sex allocation of the form just described is well-studied in the parasitic wasps. However, the factors affecting sex allocation in haplodiploid herbivores are much less understood, though these herbivores are very common and quite often cause major economic damage (e.g., spider mites and sawflies). In addition, herbivory is probably a primitive state in many haplodiploid groups and an understanding of gender control will allow a better understanding of the evolution of herbivory. The proposed research will examine the relationship between sex allocation in haplodiploid herbivores and the variable quality of host-plants encountered. By examining diverse groups of haplodiploid herbivores, i.e., sawflies and spider mites, in which haplodiploidy arose independently, the investigators hope to define the evolutionary generalities that led to the success of this genetic system. A further aspect of this research is the relationship of population sex ratios to rates of population increase. By determining host-plant factors that result in the production of relatively greater proportions of females, the investigators will also begin to determine the host-plant factors responsible for periodic outbreaks of haplodiploid herbivores. In addition to survivorship, growth rate and egg production, the relative proportion of females in a population is a parameter with potentially large consequences for population growth rates. The ability to alter the sex ratio of hapodiploid herbivores through manipulation of their host plants could lead to an additional method of controlling many pests in agriculture and forestry. *** //
