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This project focused on field evaluations of synthetic host and pheromonal odor combinations for attractiveness to plum curculios, Conotrachelus nenuphar (Coleoptera: Curculionidae), with the aim of developing a monitoring device that could track the onset and extent of immigration into apple orchards, thereby maximizing plum curculio control while minimizing exposure and cost by helping growers to accurately time insecticide sprays. In a 2000 field test I screened six individual host plant volatiles, each in association with grandisoic acid (synthetic plum curculio aggregation pheromone), using panel and pyramid traps. Benzaldehyde was the most attractive host plant odor when in combination with grandisoic acid. Evaluations conducted in 2001 confirmed the attractiveness of this binary combination to both males and females across the entire period of immigration, and also revealed that benzaldehyde interacts in a synergistic manner with grandisoic acid. Additional field studies conducted in 2002 and 2003 showed that benzaldehyde at 40 mg/day of release in association with grandisoic acid at 1 mg/day of release is the most cost-effective bait combination for use in traps to monitor plum curculio immigration. I also investigated temporal dynamics of plum curculio immigration into an unsprayed section of an apple orchard over a five-year period using traps. My main goal was to determine relationships among the timing of immigration, temperature and phenological tree stage. Based on my data, I propose a pre- and a post-petal-fall period of immigration, each of which is influenced to a different extent by spring temperature. Thermal constants (expressed in Degree Days [DD] base 6.1°C, computed starting January 1st) for the start of immigration, 50th and 80th percentile of cumulative captures were 113, 249 and 412 DD, respectively. Some spatial aspects of plum curculio immigration were also studied in commercial apple orchards over a two-year period. By petal fall, most adults were found on perimeter-row trees in sprayed blocks having large trees (M.7 rootstock), but more adults were found inside of blocks than on perimeter-row trees if blocks had small trees (M.9 rootstock). Plum curculios were able to overwinter inside blocks, regardless of the presence or absence of weeds beneath trees.

Mutualisms are major structuring forces in biological communities. However, the concept of the trophic cascade has rarely been explicitly applied to mutualisms. Antagonists of one mutualist have the potential to negatively affect the second mutualist through effects on their partner, and the magnitude of such effects should vary with mutualism strength. Bumblebees represent an ecologically and economically important mutualist pollinator group. They are attacked by a range of parasites, and visit a variety of plants that vary in reliance on bumblebees for pollination service. Using bumblebees and their parasites, I investigated whether mutualisms can mediate trophic cascades. I surveyed three parasites (Crithidia bombi, Nosema bombi and conopid flies) in Bombus spp. in Massachusetts and found that parasites are more common in wild bumblebees than previously believed (Chapter 1). To test whether infection by these parasites has top-down effects on pollination service to plants, I examined whether site-level parasitism rates correlated with pollination service to greenhouse-raised plants. I used several plant species which varied in their dependence on bumblebees for pollination. The relationship between parasitism and pollination service differed between plants and parasite species, and there was evidence that plants more reliant on bees for pollination experienced stronger negative indirect effects of parasites (Chapter 2). Finally, I developed an ordinary differential equation model of mutualist population dynamics incorporating a producer, its mutualist, and an antagonist of the mutualist. I varied the mutualism from obligate to facultative, and investigated effects of the antagonist on mutualist coexistence. My results highlight how mutualisms differ from traditional trophic cascades, and the importance of considering obligate, facultative, and asymmetric mutualisms in attempting to understand their interactions with the community (Chapter 3). My contributes to conservation issues and extends our theoretical understanding of basic ecology. I provided valuable data about the incidence and multitrophic effects of parasites in an important native pollinator. By combining mutualisms with the theoretical structure of the trophic cascade, two previously independent areas of ecological research that will benefit from integration, my research improves our understanding of how mutualisms structure the community as a whole.

The pine-needle scale insects; Chionaspis pinifoliae and C. heterophyllae are armored scale insects (Hemiptera: Diaspididae) with extensive native ranges throughout North America. In particular, C. pinifoliae is found on almost every species in the genus Pinus. Both species are economically important pests on pines, and over a century of scientific literature has considered these as only two morphological species. The life history of scale insects suggests they may form strongly structured metapopulations, resulting in high rates of host race formation and possibly speciation. Such newly originated species are likely to be morphologically similar. The geographic distribution and host use of these two species suggests they may represent a group of species that have gone unsampled due to their broad distribution or unrecognized due to their similar morphology. To explore the potential for species diversity in pine-needle scale insects I collected 366 individual insects from 320 localities across North America, representing 51 host species within the Pinaceae. I estimated species diversity by inferring species boundaries using genealogical concordance across allele genealogies of two nuclear loci and one mitochondrial locus. Using Maximum Likelihood allele genealogies in a majority-rule consensus to assess congruence, I conservatively detect 10 species in this group. However some of these 10 species contain morphological subgroups that conventional taxonomy would recognize as their own species. I explored alternate species delimitations using a range of species delimitation schemes based on genealogical concordance and mitochondrial divergence. I analyzed these delimitation schemes as species in a Bayesian species tree analysis, and infer that a delimitation of 26 species is the optimum scheme. This 26-species scheme also recognizes most of the aforementioned unique morphological subgroups, as species. Additionally, the genetic analyses for the above work occasionally recovered parasitoid sequences, from the 28S D2 and D3 subunits of ribosomal RNA. I included these sequences in a phylogeny of over 500 specimens from 18 of 19 families within the Chalcidoidea. I compared the phylogenetic results against a comprehensive list of parasitoids recorded from C. pinifoliae and C. heterophyllae, and find the 28s sequences indicate the parasitoid diversity utilizing these pine-feeding scale insects is much higher than previously thought.

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The genital chamber is a structure that is important for mating, egg progression, and fertilization in female crickets. The activity and efferent control of the genital chamber and its retractor, muscle 2, are characterized using electrophysiology, intracellular dye injections, and immunohistochemistry in a dissected preparation of female Acheta domesticus. Rhythmic activity in nerves 7v and 8v underlies movements of the genital chamber, and rhythmically-active motor neurons in the terminal abdominal ganglion supply the genital chamber and muscle 2. Some of these motor neurons were identified on the basis of intracellularly-recorded activity, axonal projections, target muscle, and/or central anatomy. Rhythmic 8v motor neurons in the terminal abdominal ganglion have two morphological types; one type shows diffuse or stringy projections and the physiological characteristic of soma spikes. Rhythmic motor neurons do not show properties such as plateau potentials, which are consistent with endogenous oscillation; it is suggested that they receive rhythmic synaptic drive. A bilateral pair of identified rhythmic motor neurons in the 8th segment contains serotonin and projects to the genital chamber. Serotonergic fibers on the genital chamber are the endings of this pair of neurons exclusively. Other serotonergic neurons in the terminal ganglion project to motor and integrative areas, and serotonin is differentially localized in sensory projection areas of the 7th and 8th versus the 9th and 10th neuromeres. These results suggest that serotonin could be involved in the modulation of mechanosensory information, as well as modulating pattern-generating circuitry in the terminal ganglion. This system presents a model for investigating the role of serotonin in neuromuscular transmission, and in the integration of neural circuits for behavior.