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Effects of temperature on development and fitness of Asian gypsy moth and the biocontrol agent of hemlock woolly adelgid, scymnus camptodromus

Author
Limbu, Samita
Published
[University Park, Pennsylvania] : Pennsylvania State University, 2017.
Physical Description
1 electronic document
Additional Creators
Hoover, Kelli
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Open Access.
Summary
The recent rise in mean annual temperature along with growth and advancement in international trade have accelerated the rate of invasion by exotic species throughout the world. Around 50,000 non-native species have been estimated to be introduced into the US (Pimental et al. 2004). Exotic species have often become pests and have caused substantial disturbances to forest and agricultural ecosystem, threatened the biodiversity, and has the potential for severe economic impacts. Hemlock woolly adelgid, Adelges tsugae (Annand) (Hemiptera: Adelgidae) and gypsy moth (Lymantria dispar L.) are examples of two non-native insects that have seriously threatened urban and forest ecosystem in the US. Hemlock woolly adelgid (HWA) since its initial introduction has steadily expanded its range in the eastern US and caused extensive damage to hemlock stands. This insect is now considered as the single most important threat to native hemlock stands in the eastern US. Similarly, gypsy moth is a major defoliator of numerous tree species in most of the northern hemisphere. In North America, the gypsy moth of European origin has been present for over 145 years and has decimated hardwood forests. Recently, introductions of Asian subspecies of L. dispar have been detected in North America potentially through international trade and it is considered a greater threat to the commercial and urban forest than the European counterparts.Not all non-native species have a negative impact because most of them do not survive in a new environment. Environmental barriers can prevent introduced species from establishing in a new location. Thus, invasion success is more likely when climatic conditions in the introduced area are similar to the native habitat of the exotic species (Walther et al. 2009). Because insect is ectotherms, temperature has a significant impact on their survival. Understanding the potential of the non-native species to colonize and establish in a new environment requires a thorough knowledge on effects of temperature on the life history of the insect. We examined the effects of temperature on growth, development and fitness of two insect species: Scymnus camptodromus and Asian gypsy moth. In an attempt to control HWA population in the eastern US, several predators were introduced from outside the pests native range and Scymnus (Neopullus) camptodromus Yu and Liu (Coleoptera: Coccinellidae) was one of them. It is a predacious lady beetle brought to the US from China as one of the potential biological control agents of HWA. The lady beetles phenology is closely synchronized with that of HWA and has several characteristics of a promising biological control agent. As a prerequisite to field release, we first evaluated the potential non-target impacts of S. camptodromus. In host range studies, the predator was given the choice of adelgid and non-adelgid prey items. Non-target testing showed that S. camptodromus will feed to some degree on other adelgid species, but highly prefers HWA. We also evaluated the larval development of the predator on other adelgid species and only a small proportion of predator larvae were able to develop to adulthood. S. camptodromus showed minimum interest in feeding on the non-adelgid species tested in choice and no-choice experiments. S. camptodromus females did not oviposit on any host material other than HWA infested hemlock. Under the circumstances of the study, S. camptodromus appears to be a specific predator of HWA, with minimal risk to non-target species. We also evaluated the effect of temperature on S. camptodromus larval development time and predation by instar and strain (geographical population). We observed that temperature had significant effects on the predator's life history. The larvae tended to develop faster and consume more eggs of HWA per day as rearing temperature increased. Mean egg consumption per day of HWA was significantly less at 15 than at 20 C. However, since larvae took longer to develop at the lower temperature, the total number of eggs consumed per instar during larval development did not differ significantly between the two temperatures. The lower temperature threshold for predator larval development was estimated to be 5 C and the accumulated degree-days for 50% of the predator neonates to reach adulthood were estimated to be 424. Although temperature had a significant effect on larval development and predation, it did not impact survival, size or sex ratio of the predator at 15 and 20 C. Furthermore, no remarkable distinctions were observed among different geographical populations of the predator. These findings on developmental rates, degree-day requirements, and predator consumption provide baseline data for developing mass rearing procedures and planning field releases of S. camptodromus. For Asian gypsy moth, because it is not yet an established pest, our goal was to develop phenology models of AGM strains in response to temperature to facilitate detection and management/eradication efforts. Predicting phenology of the Asian gypsy moth is critical for monitoring and management. For instance, Bacillus thuringiensis kurstaki (Btk), a preferred treatment for Asian gypsy moth control, is most effective if applied to the early second instar (Reardon et al. 1994). Currently, phenology of the gypsy moth is predicted based on the European subspecies and by climate matching, which may not be accurate for the Asian subspecies. In this study we evaluated the development of eight strains of AGM from a broad range of geographic latitudes reared on artificial diet at five constant temperatures (10-30 C). Our results suggest that AGM larvae developed faster as rearing temperature increased until it reached an optimum at 29 C. Larvae displayed significant molting problems at the highest and lowest temperatures tested (10 and 30 C), and at 30 C female fitness was markedly compromised, as evidenced by reduced fecundity and fertility. These findings suggest that development and survival of Asian gypsy moth may be limited by summer temperature extremes in the southern US. We also determined the degree-day requirements for two critical life stages (from egg hatch to second instar and egg hatch to adult) to predict the timing for both bio-pesticide application and adult trapping. Our data will benefit pest managers in developing management strategies, pest risk assessments, and timing for implementation of management tactics.
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Dissertation Note
Ph.D. Pennsylvania State University, 2017.
Reproduction Note
Microfilm (positive). 1 reel ; 35 mm. (University Microfilms 13918129)
Technical Details
The full text of the dissertation is available as an Adobe Acrobat .pdf file ; Adobe Acrobat Reader required to view the file.
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