Non-nutritive Sugars as a Management Tactic for Spotted-Wing Drosophila (Drosophila suzukii) and Non-Target Effects

With confirmation of non-nutritive sugar, erythritol, having insecticidal properties to Dipterans, this thesis research focuses on use of erythritol as a human-safe management tool for small berry and cherry pest, Drosophila suzukii, commonly referred to as spotted-wing drosophila. Drosophila suzukii is a destructive invasive fruit fly from Asia with an advantageous ovipositor that allows females to lay eggs into ripening fruit. Current pest management involves revolving insecticide application of various classes of insecticides despite the well-known detrimental impacts to the environment, human health, and beneficial insects. This thesis covers three main topics concerning use of erythritol when combined with sucrose and another sweet non-nutritive sugar, sucralose. Erythritol has insecticidal properties to D. suzukii if they consume a lethal dose, so our formulation uses 1.5 molar concentration and is combined with something sweet to entice flies to feed a large amount. Testing sucralose is of particular interest because an erythritol+sucralose combination would be completely non-nutritional to spotted-wing drosophila, which consequently has potential to quicken mortality if flies are unable to use sucralose for energy. First, laboratory tests were performed directly comparing efficacy between erythritol+sucrose and erythritol+sucralose formulations on D. suzukii feeding preference, survival, and oviposition behavior. We found that erythritol combined with sucralose enhanced feeding, quickened mortality, and reduced oviposition rates, in comparison to erythritol+sucrose combination; thus, we suggest that sucralose could be a suitable, non-nutritional phagostimulant and replace sucrose for our purposes. Second, we explored how D. suzukii metabolizes sucralose as it is a chlorinated form of sucrose. We performed various physiological experiments to investigate whether sucralose can be converted to a usable carbohydrate in the fly body or if it is truly non-nutritive. Much like erythritol, sucralose consumption leads to starvation, heightened pressure inside the body and desiccation that negatively effects fly survival. Through anthrone and vanillin tests, we found that D. suzukii cannot convert sucralose to any usable bodily carbohydrates or storage in lipids. Third, we conducted multi-year field trials to test performance of our two erythritol formulations on blueberry cultivars and examined non-target impacts to honeybee brood (Apis mellifera) and western yellow jacket (Vespula pensylvanica). During both years of field trials, leaf damage was observed which could indicate that our sprays are slightly phytotoxic to the various blueberry cultivars, although there was no detectable negative impact of our sprays on blueberry fruit quality (firmness, size, penetration force to pierce fruit epidermis and °Brix). Additionally, during field trials, yellow jacket visitation was plentiful to both erythritol+sucrose and erythritol+sucralose sprayed bushes. Yellow jackets are considered nuisance pests, thus we tested toxicity of these treatments by feeding these compounds to adults in a feeding assay. Our results showed little to no toxicity of erythritol or sucralose to yellow jackets. Honeybee visitation was scarce and similar among all treatments which indicates that they are not lured towards the sweet sprays. Although there was minimal visitation, the impacts of our erythritol treatments to honeybee brood was still of interest and this was tested by directly dripping treatment solutions into larval brood cells and monitoring mortality until completion of adult development. Our results showed that there is no detectable difference in toxicity of both erythritol and sucralose to honeybee brood in comparison to control (distilled water). Our formulations, erythritol+sucrose and erythritol+sucralose, kill and reduce oviposition of spotted-wing drosophila efficiently in lab settings, but were inconclusive in field settings because of low wild D. suzukii infestation rates and abnormally hot weather. This work provides vital non-target information as both of our formulations cause negligible non-target damage to blueberry fruit, yellow jackets, and honeybees

"The un-bee-lieveable need for consistent population surveying"

Lightning Tal

Factors affecting the biology of Pachycrepoideus vindemmiae (Hymenoptera: Pteromalidae), a parasitoid of spotted-wing drosophila (Drosophila suzukii).

Pachycrepoideus vindemmiae is a wasp that parasitizes and host-feeds on pupae of the invasive spotted-wing drosophila (SWD, Drosophila suzukii). Few studies have addressed interactions between these two species and little is known about the potential of this parasitoid as a biocontrol agent of SWD and the different variables that may affect it. Here, we investigated the impact of extrinsic and intrinsic factors on life-history traits of P. vindemmiae. Both constant (entire adulthood) and limited (30 minutes) supplies of water + honey, honey, or host increased parasitoid survival compared to controls (water or fasting). Water + honey caused the highest parasitoid survivals (35-60 days), independent of supply period, sex, and host availability. Females were intrinsically more resistant to water- and honey-deprivation than males, and host-feeding elevated such resistance even higher. Constant honey supply (either with or without water) supported the highest host-killing capacities (= capacity to kill hosts) (ca. 600 SWD pupae/wasp). However, in young females (4-9 days old), the impact of honey availability (with or without water) was insignificant while water deprivation (either with or without honey) caused the highest host-killing potential. This indicates that although sugar becomes a critical nutritional resource as females age, young females depend more on water than sugar to reproduce. Neither water nor honey affected the sex ratio of young females, but when we considered the entire adulthood, the availability of honey caused the lowest proportion of females (0.50), independent of water availability. Neither water nor honey affected parasitoid emergence rate (0.97), independent of female age. Based on survival and host-killing capacity, we conclude that P. vindemmiae has a tremendous biocontrol potential against SWD. Both limited and constant supply of water, sugar, and host increase parasitoid survival, while constant supply of water and/or honey enhance its host-killing potential and decrease sex ratio depending on maternal age

\u3ci\u3eDrosophila\u3c/i\u3e Muller F Elements Maintain a Distinct Set of Genomic Properties Over 40 Million Years of Evolution

The Muller F element (4.2 Mb, ~80 protein-coding genes) is an unusual autosome of Drosophila melanogaster; it is mostly heterochromatic with a low recombination rate. To investigate how these properties impact the evolution of repeats and genes, we manually improved the sequence and annotated the genes on the D. erecta, D. mojavensis, and D. grimshawi F elements and euchromatic domains from the Muller D element. We find that F elements have greater transposon density (25–50%) than euchromatic reference regions (3–11%). Among the F elements, D. grimshawi has the lowest transposon density (particularly DINE-1: 2% vs. 11–27%). F element genes have larger coding spans, more coding exons, larger introns, and lower codon bias. Comparison of the Effective Number of Codons with the Codon Adaptation Index shows that, in contrast to the other species, codon bias in D. grimshawi F element genes can be attributed primarily to selection instead of mutational biases, suggesting that density and types of transposons affect the degree of local heterochromatin formation. F element genes have lower estimated DNA melting temperatures than D element genes, potentially facilitating transcription through heterochromatin. Most F element genes (~90%) have remained on that element, but the F element has smaller syntenic blocks than genome averages (3.4–3.6 vs. 8.4–8.8 genes per block), indicating greater rates of inversion despite lower rates of recombination. Overall, the F element has maintained characteristics that are distinct from other autosomes in the Drosophila lineage, illuminating the constraints imposed by a heterochromatic milieu