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Life Table and Population Dynamics of the Cotton Aphid, Aphis gossypii, on Upland Cotton

Parajulee, Megha N.
The Southwestern entomologist 2014 v.39 no.3 pp. 401-410
Aphis gossypii, Gossypium hirsutum, cages, canopy, cotton, fecundity, growing season, heat sums, instars, irrigation, leaves, life history, life tables, longevity, monitoring, mortality, nymphs, population growth, temperature
Controlled field studies using clip cages were used to quantify development, reproduction, and survival, and generate life history characteristics and population growth parameters of the cotton aphid, Aphis gossypii Glover, on irrigated upland cotton, Gossypium hirsutum L. Newly born (<6-hour-old) aphid nymphs were individually placed on the underside of fifth mainstem cotton leaves (n = 30 plants). Aphids were monitored every 24 hours and the developmental stage, fecundity, and mortality recorded until the last aphid from the cohort died. Individual aphids were transferred to a new fifth leaf on the same plant when plants gained a newer leaf. Average daily temperature under the leaf surface was 28.1°C. Nymphal durations were 38, 48, 37, and 34 degree-days above a development threshold of 6.3°C for 1ˢᵗ, 2ⁿᵈ, 3ʳᵈ, and 4ᵗʰ instars, respectively. Aphids began dying at 448 degree-days, and the last individual in the cohort died at 907 degree-days, with an average longevity of 674 degree-days. The gross reproductive rate and finite rate of increase were 62.24 and 1.43263, respectively. A complementary study was done by daily monitoring population dynamics and within-plant distribution of the aphid for two growing seasons. Cotton aphids were not typically in the field until mid-July or early August, and the population decreased after mid-September. A fifth mainstem leaf from the top of the plant canopy (T₅) and a leaf from the mid-canopy (M) consistently tracked population activity with whole-plant densities, suggesting that either T₅ or M should serve as a reliable indicator-leaf for monitoring cotton aphid population dynamics in the field.