The Intrinsic Rate of Growth of Soybean Aphid, Aphis Glycines Matsumura, Under Different Systems of Soybean Production
The soybean aphid, Aphis g/ycines Matsumura is an invasive species that first made its appearance in the U.S. in the year 2000 infesting soybean, Glycine max L. Since then the aphid has been very successful in propagating and is now abundant in soybean fields all over the Midwest. The aphids show remarkable population growth, due in part to parthogenetic reproduction, and can go from a few aphids per plant to thousands in a matter of weeks. Yield loss has been recorded as high as 40% for heavily infested fields. In this study an attempt was made to estimate the intrinsic rate of growth, rm, for the aphids under field conditions minus predation, for different agronomic treatments. These treatments include conventional, no-tilling, and zero-chemical input. A cohort population of aphids was placed in clip cages, which were subsequently checked every 24 hours, at which time nymphs were counted and removed. From the data we were able to calculate r m values using the simplified Wyatt and White method of 0.301, 0.325, and 0.328 for the three treatments respectively. Under the classical Birch equation for intrinsic rate of growth the rm values were: 0.221, 0.229 and 0.229 respectively. These estimates should help to give researchers interested in the control of this invasive species and idea of how fast the aphid population will grow in a certain period of time as well as suggesting bottom-up effects of host-plant quality on the reproductive success of the soybean aphid. This investigation shows particular interest in the higher r m values as compared to previous studies in the aphid's native range .
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