Genetic Population Structure of Pecan Nut Casebearer Pherotypes
The pecan nut casebearer, Acrobasis nuxvorella, is the most damaging pest of pecan. Early season management of this key pest prevents losses of ca. $30 million/yr. 33-56% of the insecticides used in the Southern Region of the US target this pest. Pheromone monitoring and sequential sampling are currently used to assess insecticide treatment needs. Reducing insecticide use is essential for conserving natural enemies of foliar pecan pests and for reducing environmental pollution. A putative cryptic strain of A. nuxvorella (recently discovered using a new pheromone construct) poses a major threat to pecan. Our research has found that these two alleged pheromone strains were pherotypes. Thus, no reproductive isolation of moths attracted to different pheromones, was detected. The two pherotypes we have described are sympatric in the US and have similar phenologies and damage characteristics. Our research project has assessed the relative ratio of the two strains across the US Southern Region. We have also assessed the population structure of A. nuxvorella in the US. Funding source: USDA-CSREE.
Host-Associated Differentiation of an Insect Pest in Cultivated and Uncultivated Vegetation
Cotton is an important crop in the Southern US. In Texas, cotton and cotton seed generate more than $2 billion annually. The adoption of transgenic cotton and boll weevil eradication has transformed cotton fleahoppers into a key pest of cotton. Preliminary studies suggest that fleahoppers from cotton and uncultivated vegetation could be reproductively isolated. Thus, uncultivated plants may not be considered as pest refuges and their treatment as a pest source could be unwarranted. The objectives of this study are to find evidence of adaptation to different host-plant species among fleahoppers; to determine odor preferences of host-associated cotton fleahopper populations; to determine if cotton fleahopper populations associated with different host-plant species are reproductively isolated and to determine the genetic population structure of the cotton fleahopper across its distribution range. Morphometric parameters are being used to detect host-plant adaptation.
Olfactometric tests are being used to determine fleahopper odor preferences. AFLP markers are being used to determine reproductive isolation among fleahopper populations associated with cotton and uncultivated vegetation and to asses the population structure of this insect in the Southern US. The findings from this multi-State study (i.e., Arizona, New Mexico, Oklahoma, Texas, Arkansas, Mississippi, Louisiana, and Georgia) will elucidate the role of uncultivated vegetation in a simple plant bug model system and should result in a reduction in the cost of cotton IPM through an improvement of management practices and more effective insecticide use thus minimizing potential human health and environmental risks with improved IPM strategies. This project is a collaborative effort between AgriLIFE RESEARCH and AgriLIFE EXTENSION. Funding Source: Texas State Support Committee
Host-Associated Differentiation in Arboreal Insect Communities
Flowering plants, herbivorous insects, and insect parasitoids together comprise more than 50% of the world’s species. Because insects often have narrow host breadths and tight associations with their hosts they are prime candidates for Host Associated Differentiation (HAD). HAD is the formation of genetically divergent host associated sub-populations. HAD has been proposed as a mechanism promoting adaptive radiation of host-associated lineages resulting over time in increased species diversity. HAD has been documented by assessing behavioral differences such as oviposition preference indicating host-plant fidelity and assortative mating; differences in fitness due to heritable morphological traits; and statistical measures of genetic differentiation between populations on different host plants. Multiple studies to date have demonstrated HAD for a single species of herbivore on related species of host-plants. Recently, some studies have also demonstrated HAD cascading to the third trophic level from insect herbivores to both parasitoids and predaceous inquilines. The purpose of the present research project is to test genetic differentiation of insects in a host-plant system where HAD is predicted to be favored utilizing a multi-trophic community approach. Testing HAD in an insect community will facilitate multiple comparisons between insects on the same host-plant system and make a contribution to our understanding of HAD. Funding Source: Department of Entomology, Texas A&M University.
Host-Associated Differentiation in Native Fruit Systems
Host-associated differentiation (HAD) is a mechanism promoting species diversity by genetically isolating subpopulations within a species adapting to new hosts. The cranberry fruitworm and the cranberry weevil have co-evolved with both cranberries and blueberries for millennia in their native habitat. If HAD is as common as the literature suggest in nature, it is likely to be found in such a system. We are testing the cranberry fruitworm, Acrobasis vaccinii Riley (Lepidoptera: Pyralidae) and the cranberry weevil, Anthonomus musculus Say (Coleoptera: Curculionidae) , for HAD by examining the genetic fingerprint of individuals associated with cranberry, Vaccinium macrocarpon Ait., compared to those living on blueberry, Vaccinium corymbosum L. (both Ericales: Ericaceae). We are collecting samples from blueberries and cranberries throughout various farms across New Jersey, Michigan and Massachusetts and performing behavioral and molecular analyses to assess the existence of HAD. The current project is a collaborative effort between Texas A&M University and Rutgers University. Funding Source: Department of Entomology Texas A&M University, Rutgers University, NSF-REU.
Influence of Host-Range in the Population Structure of Parasitoids
Parasitoids with different host-ranges (i.e., specialist versus generalist) may differ in the way their populations are geographically structured. We are currently exploring if host-range influence the way parasitoid populations are structured genetically. We hypothesize that generalist parasitoids will tend to be less mobile than specialist parasitoids due to their ability to oviposit in more than one host-species. In contrast, specialist parasitoids are predicted to have a less geographically structured population due to their hypothesized tendency to search for hosts by moving larger distances. This hypothesis is being tested, in collaboration with Saskya Van Nouhuys, using a generalist and a specialist parasitoid of the fritillary butterfly (Melitaea cinxia) in the Åland Islands in Finland. Similarly, we are testing this hypothesis with a generalist and a specialist parasitoid of the main European pine forest pests, the pine processionary moth, Thaumetopoea pityocampa Denis & Schiffermuller (Lepidoptera: Notodontidae) on its two main host plants in Italy (i.e., Pinus nigra and Pinus sylvestris). This last project is a collaborative effort between Texas A&M University and The Università degli Studi di Padova. Knowledge on the influence of host-range in the population structure of parasitoid species will provide insights into effective ways to release natural enemies in bio-control. Funding Source: Van Nouhuys lab, Università degli Studi di Padova, Texas A&M University.