Thesis (PH.D.) -- Syracuse University, 2006 / "Publication number AAT 3251760."

The cranberry fruitworm, Acrobasis vaccinii (Riley) (Pyralidae), is the most important insect pest of Massachusetts cranberries. The female lays her eggs individually in the calyxes of developing fruits. Upon hatching, the larva cats its way into the fruit and consumes it, whereupon it moves to another. Because the immatures are protected inside fruits, insecticides target the adult and egg stages. Growers wishing to practice integrated pest management (IPM) engage scouts to collect and check berries for eggs to determine whether spraying is warranted. However, their protocol was devised with limited knowledge of egg distribution or the relationship between eggs found and yield loss. Better understanding of the oviposition behavior of the female and of egg distributions is essential for effective monitoring. The quest to optimize scouting efficiency led me to explore the physical properties of cranberries and their immediate environment in order to identify factors influencing oviposition. Mechanosensory stimuli, including surface texture, conformation, size, geoörientation, and moisture content of the oviposition substrate, are important determinants in insect oviposition site selection, comprehensively reviewed in Chapter 1. In laboratory choice experiments described in Chapter 2, I manipulated the surface texture, conformation and geöorientation of cranberries and showed that physical contact with a natural calyx is important in eliciting oviposition. In field choice experiments, I showed that females are more likely to oviposit on the uppermost berries and on berries growing in abundant foliage. The balance of my research was designed to characterize the egg spatial distribution in commercial cranberry bogs and to develop an empirically-based IPM scouting protocol. Six bogs were intensively sampled and their egg distributions were modeled in Chapter 3 using Taylor's Power Law (Taylor, 1961), variance = a*meanb. However, exponential and logarithmic versions of the model produced different regressions. Comparisons of their performance demonstrated that exponential models usually produced more satisfactory descriptions of the variance to mean relationship. Analyses of the published data sets Taylor employed, presented in Chapter 4, obtained comparable results. In Chapter 5, I developed and tested a new scouting protocol based on the exponential model, which outperformed the original protocol in field trials.

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.

The mosquito Aedes aegypti is the primary worldwide vector of dengue fever, of which there are an estimated 390 million infections annually. Traditional vector control methods have been unsuccessful in preventing Ae. aegypti from posing a serious threat to human health worldwide, and as a result increasing emphasis is being placed on new control technologies. One of these is RIDL® (Release of Insects carrying a Dominant Lethal), a modified form of the sterile insect technique. Released RIDL males of strain OX513A are genetically engineered to possess a repressible lethal construct. Upon mating with a wild female, the construct is inherited by the offspring, causing their death. The RIDL strategy depends on the mass production and release of vigorous male insects, capable of competing with wild males to mate with wild females. <b>Chapter 2</b> investigates how rearing conditions can influence the size, asymmetry, quantity, and timing of OX513A mosquitoes produced. <b>Chapter 3</b> describes the design and testing of devices for the release of these adult males, and their implementation during the world's first release of transgenic mosquitoes. <b>Chapter 4</b> discusses how the modification of male size and nutritional status may affect subsequent performance, and how these changes to male vigour will be assessed in subsequent chapters. <b>Chapter 5</b> measures changes in competitiveness by examining longevity. Larger males lived longer, and longevity was increased by increasing the duration of the initial sugar feed. <b>Chapter 6</b> examines the potential improvements in male performance by measuring the flight capacity of OX513A males, using a purpose-built mosquito flight mill. Male size or nutritional status was not found to affect flight capacity, although light intensity was unexpectedly found to modulate the flight speed of the males. Finally, <b>Chapter 7</b> examines potential improvements in the mating performance of male OX513A Ae. aegypti. When OX513A males and wild-type males were placed in direct competition for virgin females, smaller OX513A males were found to have a significant mating advantage over larger wild-type males. The results of all three of these performance measures are discussed with relevance to field releases. The results presented in this thesis improve current knowledge of how the performance of male mosquitoes can be effectively measured and improved. This is a vital part of ensuring the success of male-release vector control strategies such as RIDL.

Insect pests represent major threats to food production, biodiversity conservation, and human and animal health. Currently, the most widespread strategy to control their populations is through the spraying of synthetic chemical insecticides. However, the overuse of these compounds has had significant negative environmental consequences. Additionally, our reliance on insecticides has resulted in major reductions in their efficacy through pest-evolved resistance. To successfully manage insect pests, while avoiding environmental degradation, thus requires the development of novel, more sustainable, pest management strategies. Recent advances in our understanding of recombinant DNA methods and molecular biology have allowed the application of transgenic tools to pest management. Here, synthetic genes can be engineered, transformed into the genomes of pest species, and transported into wild target populations through the natural mating behaviour of the insect. A strategy in which these transgenes are lethal to those insects inheriting them in the field is known as RIDL – Release of Insects carrying a Dominant Lethal. A variant of RIDL limits this lethality to females – female specific RIDL (fsRIDL) – which explicitly targets the reproductive capacity of a target population. The aim of this thesis is to investigate the application of such an fsRIDL strategy to the diamondback moth (Plutella xylostella L.). This economically important pest of brassica crops is highly adept at developing resistance to insecticides and is considered extremely difficult to manage effectively. I present findings which demonstrate the power of diamondback moth lines transformed with fsRIDL transgenes to eliminate target pest populations, and combine synergistically with other transgenic control strategies such as Bt crops in counteracting the evolution of pesticide resistance. Additionally, an exploration into an alternative gene expression system to that used in current RIDL strategies – the Q system – suggests that not all expression systems will be suitable for transgene control within this highly specific framework. It is hoped that this work will contribute towards the effective control of the diamondback moth, and form a model for the sustainable control of other lepidopteran species through genetic pest management.