ABSTRACT

Title of Document: THE ROLE OF HOST-PLANT SPECIES IN THE DIFFERENTIATION OF SYMPATRIC POPULATIONS OF HYMENOPTERAN PARASITOIDS.

Raul F. Medina, PhD, 2005

Directed By: Professor, Pedro Barbosa, Department of Entomology

The biology and ecology of insect parasitoids is strongly influenced by the host-plant species on which their herbivorous hosts occur. Hymenopteran parasitoids in particular, present a series of characteristics that made them good candidates for phenotypic and genotypic differentiation. Thus, parasitoid adaptation to plant traits may promote significant phenotypic and genotypic differences among sympatric populations of parasitoids associated with different host-plant species. The present study assessed phenotypic and genotypic differentiation in two braconid parasitoids ovipositing on the same host species, the green cloverworm, Plathypena scabra Fabricius (Lepidoptera: Noctuidae) feeding on alfalfa and soybean. Developmental time, adult weight, percent parasitism and preference for host-plant odors of the generalist parasitoid Cotesia marginiventris Cresson (Hymenoptera: Braconidae) and of the specialist parasitoid Aleiodes nolophanae Ashmead (Hymenoptera: Braconidae) were compared among individuals ovipositing in green cloverworm larvae feeding on alfalfa and soybean. In addition, amplified fragment length polymorphisms (AFLP) were used to assess if genotypic differentiation between parasitoids ovipositing on green cloverworm larvae feeding on different host-plant species (i.e., alfalfa or soybean) was present. Phenotypic differentiation in adult mass, adult longevity and percent parasitism between parasitoids ovipositing green cloverworm larvae on alfalfa and on soybean were found. These phenotypic differences between parasitoids associated with different host-plant species were observed in both the generalist and the specialist parasitoids. No evidence of parasitoids showing preferences for the host-plant species from which their host fed was found in the generalist nor in the specialist parasitoid. Contrary to the expectations and predictions from the literature, these parasitoid species did not show evidence of reproductive isolation when associated with different host-plant species (i.e., alfalfa or soybean), as evidenced by the lack of genetic differentiation in AFLP profiles between parasitoids associated with alfalfa and soybean. In order to ensure that the number of wasps and the number of AFLP bands used were enough to provide an accurate assessment of genetic differentiation among wasps ovipositing hosts on different host-plant species, a method for determining the minimum number of individuals and AFLP bands to include to obtain accurate genetic profiles of hypothesized populations was proposed.