Interactions in Entomology: Aphids, Aphidophaga and Ants in Pecan Orchards

Abstract

Three methods for conserving aphidophaga were tested in multiple factor controlled field experiments over two seasons in four pecan, (Carya illinoensis Wangenheim (K. Koch)) orchards. Two of the orchards were planted in the 1920's and had closed canopies; and the other two were planted in 1976 and 1985 and had open canopies. Intercrops of hairy indigo (Indigofera hirsuta L.) and hemp sesbania (Sesbania exaltata [Rafinesque-Schmaltz] Cory), sown as summer annuals in strips between tree rows, a chemical barrier sprayed on the tree trunk preventing foraging of the red imported fire ant (Solenopsis invicta Buren) in the tree crown, and a predator attractant were tested in these experiments. Significant interaction effects were found in blackmargined aphid (Monellia caryella (Fitch)), ladybeetle (Coccinellidae), and red imported fire ant abundance. On most sample dates there were no differences among treatments in abundance of pecan aphids or aphidophaga, whereas, on certain sample dates aphids were significantly reduced by the combination of enhancement techniques or one enhancement technique. Intercrop treatments did not affect red imported fire ant activity on most sampling dates. Hairy indigo intercrop was associated with season-long reductions in ant activity in the pecan tree at a young orchard in 1994 and not 1993. Seasonal changes in ant foraging were the same in the tree, the herbicided areas of the orchard and the areas with intercrops at one of the old and differed at one of the young orchards. Ladybeetle abundance was higher in the trees on certain sample dates where ants were excluded from the tree. In laboratory observations, cowpea aphid (Aphis craccivora Koch) was not an acceptable prey for multicolored Asian ladybeetle (Harmonia axyridis Pallas). Cowpea aphids were eaten by convergent lady-beetle (Hippodamia convergens Guerin-Mineville). Multicolored Asian ladybeetle were more effective than convergent ladybeetle in preventing aggressive red imported fire ants from forcing them off the plant.