Crop colonisation, feeding, and reproduction by the predatory beetle, Hippodamia convergens, as indicated by stable carbon isotope analysis
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1. Habitat management to enhance natural enemy populations in agricultural systems may help regulate levels of crop pests, but little research addresses the behaviour of immigrating beneficial insects. 2. Stable carbon isotopes were used in complementary laboratory and field studies to examine colonisation behaviour of an ephemeral agricultural habitat by the lady beetle, Hippodamia convergens Gurin-Mneville. 3. Under laboratory conditions, H. convergens carbon isotope ratios, 13C, changed after its food supply was shifted from a C4- to a C3-based diet of aphids produced on grain sorghum or cotton respectively. Final isotope ratios of adult H. convergens were closer to that of the new C3-based diet, with most change in 13C occurring within 3 days after the diet shift. 4. The carbon isotope ratios of lady beetle adults collected in cotton fields suggested that grain sorghum was a continuous source for H. convergens until many nearby sorghum fields matured and senesced. 5. When cotton aphid (Aphis gossypii Glover) prey were absent, carbon isotope ratios of beetle populations did not change over time and virtually no egg production by H. convergens was detected. This indicates that beetles were feeding little on non-aphid resources originating in cotton. 6. With cotton aphids present, beetle isotope ratios decreased towards the carbon isotope ratio of cotton, indicating adult feeding in cotton. As a result, egg masses produced had carbon isotope ratios in the C3 range of values. 7. The results suggest that some predator species may be retained in habitats without large prey populations, a quality essential in controlling pests in agricultural systems.
author list (cited authors)
Prasifka, J. R., Heinz, K. M., & Winemiller, K. O.
complete list of authors
Prasifka, JR||Heinz, KM||Winemiller, KO