Browsing by Author "Ed Vargo, Committee Member"

Filter results by typing the first few letters
Now showing 1 - 2 of 2
  • No Thumbnail Available
    Interactions Between a Specialist and Generalist Moth and Their Host Plants
    (2009-12-03) Petzold, Jennifer Lee; Wendy Boss, Committee Co-Chair; Ed Vargo, Committee Member; Thomas Wentworth, Committee Member; Fred Gould, Committee Co-Chair
    Among the most significant issues regarding plant-herbivore interactions today are 1) elucidating the genetic architecture of host plant use and determining what factors are involved in locating and ovipositing on host plants, 2) understanding chemical interactions between insects and their host plants, and 3) understanding how plants evolve in response to the ecological pressures imposed on them by their insect pests, and how these insects in turn respond to these evolved mechanisms of host plant defense. The purpose of this research was to address these questions using a model system composed of two Heliothine moths, Heliothis subflexa and H. virescens. Heliothis subflexa (Hs) is a specialist that feeds only on plants in the genus Physalis, while H. virescens (Hv) is a broad generalist. To determine what genetic factors are involved in changes in host range, these two species were hybridized, and backcrosses to both parent species were produced. Larval feeding preference of Hs, Hv, and backcross lines was assessed using choice and no choice feeding tests on Physalis and tobacco (a host of Hv), and oviposition behavior was assessed by observing moths in a large outdoor cage containing Physalis and tobacco. We found that backcrosses in the Hs direction always resembled Hs in feeding and oviposition preference. Backcrosses in the Hv direction resembled Hv in oviposition behavior, but had intermediate feeding behavior and fed on both Physalis and tobacco. Hybrids showed strong preference for tobacco in oviposition behavior. These results show that at least one major locus is likely involved in feeding preference between the two host plants and that preference for Physalis is a dominant trait; however, genetic control of oviposition behavior on the two host species is more complicated to understand, possibly involving multiple genetic loci and a threshold effect, or few genes and a heterozygous disadvantage. Field experiments were also conducted to determine how Hs locates its host plants. Results showed that vision is an important host location cue, and confirmed prior studies that showed that Hs lays approximately 20% of its eggs on nearby non-hosts. A possible reason for this could be to avoid host plant defenses Physalis plants were observed to respond to eggs of Hs; they do so by forming undifferentiated cells or a hypersensitive response directly under some Hs eggs. Laboratory and field studies demonstrated that eggs that elicited a response had a 25% lower probability of hatching, and a 28% lower probability of remaining on the plant. This resulted in a fitness cost of 18% for Hs, and it was concluded that response to eggs could be a factor that selected for non-host oviposition by Hs. Plants in this genus have also evolved to abscise fruits in response to fruigivory by Hs, but the degree to which chemical interactions are involved in this defense response was unknown. By using a combination of mechanical damage, natural damage, and Hs saliva and regurgitant treatments applied to fruit, it was determined that mechanical damage was sufficient to cause fruit abscission and insect oral secretions were not important in this response.
  • No Thumbnail Available
    Modified Drone-Brood Removal to Control Varroa destructor in Apis mellifera Colonies
    (2009-07-14) Wantuch, Holly Anne; David Tarpy, Committee Chair; Wes Watson, Committee Member; Ed Vargo, Committee Member
    The parasitic mite Varroa destructor Anderson and Trueman (Acari: Varroidae) has plagued European honey bees (Apis mellifera L.) in the Americas since its introduction to the United States in the 1980s. For many years, these mites were sufficiently controlled using synthetic acaricides. Recently, however, beekeepers have experienced increased resistance by mites to chemical pesticides, which are also known to leave residues in hive products such as wax and honey. Thus, there has been increased emphasis on non-chemical IPM control tactics for Varroa. Because mites preferentially reproduce in drone brood (pupal male bees), we developed a treatment strategy focusing on salvaging parasitized drones and removing mites from them. In our initial study, we tested 10 colonies of honey bees in each of four treatment groups: 1) negative control (no treatment); 2) positive control (treatment with fluvalinate); 3) periodic drone-brood removal and freezing; and 4) periodic drone-brood removal and return of adult drones to colony after physically removing any mites. We found that there were no significant differences measured between the mean mite levels of the treatment groups (P> 0.05). However, there were numeric trends indicating that both drone-brood removal groups were intermediate in mite levels compared to the negative and positive controls. In a subsequent study, we removed drone brood from colonies in which there is no acaricidal application and banking it in separate “sacrificial†colonies treated with pesticides to kill mites emerging with drones. We tested 20 colonies divided into three treatment groups: 1) negative control (no mite treatment); 2) positive control (treatment with fluvalinate and thymol); and 3) drone-brood trapping. Two colonies were selected from the drone-brood trapping group to serve as sacrificial colonies. We found that drone-brood trapping significantly lowered mite numbers during the early months of the season, eliminating the need for additional control measures in the spring. However, mite levels in the drone-brood removal group increased later in the summer, suggesting that this benefit does not persist throughout the entire season. We recommend that drone-brood trapping can be utilized as an element of an integrated control strategy to control varroa mites. If implemented successfully, this method of drone-brood removal and rescuing may serve to eliminate a large portion of the Varroa population with limited chemical treatments, while simultaneously retaining any benefits of having adult drones in the colony.