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Intraguild Predation Among Aphidophagous Lady Beetles
Department of Entomology
This project will increase our understanding of the chemical ecology of intraguild predation among invasive and native species of Coccinellidae in North America. Previous laboratory studies have documented intraguild predation among Coccinellidae, but the underlying role of alkaloid defenses has not been examined for most species. An additional aspect of this study will address the effect of the invasive predatory species (Harmonia axyridis) as an intraguild predator of several native species of Coccinellidae. This work will provide a better understanding of the role of multiple species of predatory Coccinellidae in the biological control of selected insect pests of agricultural crops.
2009 Project Description
We conducted multiple laboratory experiments and a field survey during the first year of this grant. In the laboratory, we developed a new technique to quantify defensive chemicals, alkaloids, from eggs and larvae of predatory ladybeetles, using gas-chromatography-mass spectrometry. The materials and methods are available in our research papers.
A post-doc was trained to use gas-chromatography-mass spectrometry. A research paper has been submitted to Oecologia on August 17, 2009. We hired and trained an undergraduate student to conduct field surveys for ladybeetles and aphid prey, and laboratory experiments. We participated as instructors in an International Organization for Biological Control (Nearctic Region Section) Ladybeetle Workshop organized by Dr. Jon Lundgren, USDA-ARS, Brooking, South Dakota, from July 7 to 10, 2009. We presented recent research topics of predatory ladybeetles, such as, biological control using predatory lady beetles, life history strategies, reproductive physiology and invasion ecology of predatory ladybeetles in North America. We also organized field surveys and laboratory sections during the workshop to educate and train graduate students and professional entomologists attending the workshop.
We documented variation in the quantity of alkaloids in eggs of predatory lady beetles, Harmonia axyridis (Pallas), Coccinella septempunctata L., and Hippodamia convergens (Guerin) using gas chromatography-mass spectrometry. The repeatability (R) of our measurements of alkaloids in eggs in an egg cluster was high (R=0.99), however, the amount of alkaloids varied significantly between egg clutches within and among females. This variation affected egg consumption by C. septempunctata larvae when they fed on H. axyridis eggs, but not for H. axyridis larvae feeding on C. septempunctata eggs.
Processing of ingested alkaloids differed between the two species. First instar H. axyridis sequestered and synthesized their own alkaloids (harmonine) when they consumed conspecific eggs. Newly molted second instars of H. axyridis contain more harmonine than they consumed. In contrast, first instar C. septempuncata accumulated a smaller fraction of the ingested conspecific alkaloids compared with H. axyridis. Coccinella septempuncata eliminated over 95% of the consumed harmonine, but nonetheless died within 3 days. Harmonia axyridis also eliminated over 74% of ingested C. septempuncata alkaloids (in contrast to the accumulation of conspecific alkaloid) and survived to the second instar.
Consumption of C. septempuncata eggs by first instar H. axyridis led to a minor reduction in weight gain (compared to a diet of aphids). In addition, feeding on C. septempuncata eggs with high alkaloid level extended development of first instars by about 10% compared to a diet of aphids, or conspecific eggs. There are many reports that consumption of eggs negatively affects survivorship and development of larval stages of predatory coccinellids however, this is the first report to show a link between heterospecific alkaloids and their toxicity and/or costs.
Kajita Y, Obrycki JJ, Sloggett JJ, Haynes KF. Intraspecific alkaloid variation in ladybird eggs and its effects on con- and heterospecific intraguild predators. Submitted to Oecologia (August 2009)
Sloggett JJ, Obrycki JJ, Haynes KF (2009) Identification and quantification of predation: novel use of gas chromatography-mass spectrometric analysis of prey alkaloid markers. Functional Ecology 23: 416-426