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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.
2010 Project Description
We conducted multiple laboratory experiments and a field survey during the second year of this grant. The study of "Intraspecific alkaloid variation in ladybird eggs and its effects on con- and heterospecific intraguild predators" was published in Oecologia. The study was presented at 1) the 57th Annual Meeting of the Entomological Society of America, December 13-16, 2009, Indianapolis, Indiana, 2) the International Organization of Biological Control, Nearctic and Neotropic Regional Sections Conference, May 11-13, 2010, Niagara Falls, Canada, 3) the 26th Annual Meeting of the International Society of Chemical Ecology, July 31-Aug 4, 2010, Tours, France, 4) the International symposium Ecology of Aphidophaga 11, September 19-24, 2010, Perugia, Italy (Kajita was an invited speaker for this symposium), and 5) the NIFA/AFRI Awardee Workshops, March 23-24, 2010, Washington D.C., and December 11-12, 2010, San Diego, California. Kajita was also invited as a guest speaker at the USDA-ARS Laboratories in Brookings, SD, November 15, 2010, and exchanged our knowledge with students and researchers at USDA-ARS and South Dakota State University.
We hired and trained an international internship undergraduate student from Maejo University, Chiang Mai, Thailand. She learned how to conduct field surveys, maintain cultures of insects, and conduct laboratory experiments in a professional scientific environment.
In the laboratory, we conducted preliminary experiments to develop a new technique to identify consumed defensive chemicals, alkaloids, in intraguild predators, by using stable isotopes: N-glutamine (15N2) and sodium acetate (1,2-13C2).
We conducted several preliminary experiments to identify the variable alkaloids in eggs and larvae of Coccinella septempunctata L., C. transversoguttata Richardsoni, C. novemnotata, and Hippodamia convergens (Guerin) using gas chromatography-mass spectrometry. We found that three Coccinella species possess the same alkaloids, coccinelline and precoccinelline. Our previous data show a link between heterospecific alkaloids and their toxicity and/or costs (Kajita et al. 2010), but this finding suggests that heterospecific alkaloids may not be toxic for these ladybeetles if the heterospecific alkaloids are similar.
We conducted several preliminary experiments to trace the consumed "heterospecific (but same alkaloids for all three species)" alkaloids using stable isotopes: N-glutamine (15N2) and sodium acetate (1,2-13C2), which could incorporate within coccinelline and precoccinelline. We dissolved 10, 20, 30, 40, and 45mg/ml of each stable isotope in either 10-15% sucrose water or 50-60% Acetone, and we painted about 1ul of each stable isotope solution using a Hamilton Repeating Dispenser on the egg surface. The solution was dried at room temperature for 2 hours before we feed the eggs to 1st instar ladybeetles.
We expected to identify the 15N or 13C labeled alkaloids in gas chromatography-mass spectrometry (GC-MS) when larvae consumed the eggs, however, we could not see any 15N or 13C labeled alkaloids in GC-MS. Therefore, we could not trace exactly the consumed heterospecific alkaloids in these predators. We will use the methods from Kajita et al. (2010) to quantify alkaloids in eggs before feeding to 1st instars followed by quantification of alkaloids in larvae when we finish the feeding experiments. These methods provide an estimate of the accumulation or reduction of consumed alkaloids by comparing the levels in eggs and larvae from the GC-MS.
Kajita Y, Obrycki JJ, Sloggett JJ, Haynes KF (2010). Intraspecific alkaloid variation in ladybird eggs and its effects on con- and heterospecific intraguild predators. Oecologia (163): 313-322, DOI10.1007/s00442-009-1551-2