The role of grain sorghum in conservation of predatory arthropods of Texas cotton
MetadataShow full item record
Four separate but complimentary studies investigated the role of grain sorghum as a predator source for Southern Rolling Plains cotton in 2001 and 2002. Objectives were to: (1) determine the timing and magnitude of predator movement between crops, (2) test putative causes of movement by manipulating prey levels at different stages of crop phenology, (3) explore the feeding and reproductive behavior of a common predator colonizing cotton, and (4) examine the effects of grain sorghum and uncultivated areas on cotton predator abundance at an area-wide scale. Rubidium mark-recapture experiments indicated grain sorghum fields produced a net predator gain for adjacent cotton. Analysis suggested two coccinellids, Hippodamia convergens Guérin-Méneville and Scymnus loewii Mulsant, were responsible for the overall pattern of predator movement. Predator movement into cotton did not appear to be concentrated at specific stages of sorghum phenology. Manipulations of aphid levels in field cages were used to determine if prey abundance or phenology influenced the movement of H. convergens into cotton. In both years, more lady beetle adults were collected on cotton during the latest stages of sorghum phenology. In the second year, relatively low aphid densities (15 per plant) appeared to influence the movement of beetles onto caged cotton. Carbon isotope ratios of H. convergens were used to assess adult feeding behavior after colonizing cotton and to determine if prey consumed in sorghum contributed to egg production in cotton. Though aphids were absent 2001, H. convergens adults stayed in cotton, did not produce eggs and apparently consumed few prey. Cotton aphids were present in 2002 and H. convergens isotope ratios changed from prey consumed in cotton. The isotope ratios of egg masses collected in 2002 indicated prey consumed in grain sorghum contributed very little to egg production in cotton. An area-wide pattern analysis suggested the abundance of grain sorghum and uncultivated areas both positively influenced cotton predator levels. While these landscape effects were less important overall than prey levels and cotton planting dates, in some sampling periods landscape composition appeared to be the most important factor in determining cotton predator levels.
Prasifka, Jarrad Reed (2005). The role of grain sorghum in conservation of predatory arthropods of Texas cotton. Doctoral dissertation, Texas A&M University. Texas A&M University. Available electronically from