The family Tephritidae encompasses more than 4400 species worldwide from 500 genera. This family is one of the largest in the order Diptera that includes over 200 species of economic importance (Christenson & Foote 1960, White & Elson-Harris 1992). Economically important fruit flies can be serious pests of fruits, nuts, and vegetables that create adverse social, political, and economic hardship around the globe (Papadopoulos 2014). Extensive research and regulatory resources have been put towards pestiferous flies to reduce established populations, prevent transfer to fruit fly free areas, and effect quarantines and eradications (Vargas et al 2014). One technique used to combat these invasive pests is the use of the male annihilation technique (MAT; a.k.a. male attractant treatment). Male annihilation technique is the deployment of a high density of traps or bait stations that consists of an attractant combined with an insecticide and matrix. Where more than one species of fruit flies attacks a single crop, management becomes even more difficult and further research is needed.
Papaya (Carica papaya L.) is a specialty crop that is of significant importance to Hawaiʻi’s diversified agriculture. In Hawaiʻi, papaya is attacked by both Bactrocera dorsalis (Hendel, est. 1945) and melon fly, Bactrocera (Zeugodacus) cucurbitae (Coquillett, est. 1895). Male annihilation technique has been used in papaya for management of both B. dorsalis and B. cucurbitae. This system presents an opportunity to test the behavioral response of two species to a binary lure system in an economically important crop. Management using MAT to date has been typically done in a single lure format that targets one species with separate trapping materials, labor, and deployment.
Given that B. dorsalis and B. cucurbitae are both routinely found in and around papaya growing areas, this study sought to understand the significance of visual and olfactory cues in resource location of papaya for both fruit fly species. It also aimed to test the application and optimization of a binary lure MAT system that would reduce the numbers of both fly species.
In a series of behavioral experiments, I quantitatively measured the host resource use of B. cucurbitae on papaya and compared the sensory modalities used by two tephritids that are currently considered a “primary” pest (B. dorsalis) and an “occasional” pest (B. cucurbitae) of papaya. I recovered twenty times more adult wild B. cucurbitae flies than B. dorsalis flies from sentinel papaya fruits placed in the largest papaya growing area in the United States. Results of visual and olfactory experiments suggest that B. cucurbitae females are not primarily attracted to volatiles emitted by papaya fruit, but rather vision seems to be the main stimulus inducing landing and oviposition. Bactrocera dorsalis appears to be equally responsive to either olfactory or visual stimuli of papaya. These observations demonstrate a potential for behavioral control using visual mimics with B. cucurbitae. Furthermore, a synergistic approach using both chemical and visual stimuli to control mature male and female fruit flies shows real promise.
I performed a series of field trials to evaluate a novel binary lure MAT for two species simultaneously, B. dorsalis and B. cucurbitae. The trials were conducted in a large papaya growing area using standard trapping methods to determine efficacy and optimization of a binary MAT system (SPLAT™, Specialized Pheromone and Lure Application Technology, ISCA Technologies, Riverside, CA) with a biopesticide (spinosad, Dow AgroSciences LLC, Indianapolis, IN). I found that a binary lure system may function as a generic MAT (ME + CL) against B. dorsalis and B. cucurbitae when populations of both species are associated in a cropping area. Binary lure formulation of SPLAT was optimized by increasing the amount of ME from 25.5% to 45% and decreasing the amount of CL from 10% to 8%. A single application containing both lures could potentially reduce labor, equipment and material costs by 50%.
Following the results of the field trials, it was important to identify any potential interspecies dependent responses of B. dorsalis and B cucurbitae using novel binary lure MAT. In a series of cage test, the number of individuals in each species was manipulated to examine if the response changed when one species occurs in greater numbers than the other. I also evaluated male attractants ME + CL at varied ratios to understand the role each lure plays on the response and capture of each species. I found no interspecies interactions. Captures for both species were not different when each species was alone, in equal numbers, or when the other species was in greater numbers. Instead, the only factor that seems to influence capture rate was measured in cages with B. dorsalis. The response of B. dorsalis amplified considerably with increase in the amount of ME formulated into binary SPLAT mixture. Response of B. cucurbitae was not influenced in the same way by increasing the amount of CL. Maximizing ME and using a lower amount of CL in a binary lure MAT at the trap or station would provide the most benefit when B. dorsalis and B. cucurbitae are in equal numbers or B. cucurbitae is the dominant species.
I further explored the potential horizontal transfer of insecticide of a binary lure MAT containing spinosad. The sprayable application, strong behavioral response to male lures, and mode of action including time to mortality induced by spinosad may facilitate horizontal transfer of insecticide. Using a series of laboratory tests, I recorded mortality of conspecific male and female flies exposed to primary fed males of B. dorsalis and B. cucurbitae. I found that horizontal transfer can occur in both males and females of both species. This transfer can occur from a single fed male to other individuals or a group of conspecifics resulting in mortality. The higher mortality of males relative to females is linked to the strong behavioral response, of males to lures. Horizontal transfers of spinosad may provide enhanced suppression of both males and females of two species in one location.
Together, the results of these experiments demonstrate that use of a binary lure in papaya systems will effectively attract and kill both B. dorsalis and B. cucurbitae. Furthermore, use of a reduced risk insecticide such as spinosad, will lead to horizontal transfer and increased mortality in the populations of both species. Thus, deployment of a sprayable binary lure MAT system with reduced risk insecticide spinosad would reduce the costs associated with materials, equipment, and labor by 50% and lead to similar mortality in the field.
|Commitee:||Daehler, Curtis, Follett, Peter, Manoukis, Nicholas C., Pinero, Jaime C., Taylor, Andrew, Vargas, Roger I.|
|School:||University of Hawai'i at Manoa|
|School Location:||United States -- Hawaii|
|Source:||DAI-B 82/1(E), Dissertation Abstracts International|
|Keywords:||Biopesticide, Fruit flies, Horizontal insecticde transfer, Lure mixtures, Male annihilation technique, Suppression|
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