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Continued Studies of Insect Population Dynamics in Crimson Clover & Refugia/Cotton Systems. Part I: Sweep & Whole Plant Sampling

W. Joe Lewis, Philip B. Haney, Sharad Phatak


Sweep, shake and whole plant sampling methods were used to monitor and compare the seasonal abundance of plant-dwelling beneficials and pests in three cotton fields in Dooly and Tift county, in the Coastal Plain region of south Georgia. The two Dooly county sampling sites were a 20 ha conservation-tilled (Crimson clover) field and a nearby 20 ha conventional-tilled (fallow) field. Samples in Tift county were taken from a 10 ha conventional-tilled field interspersed with six permanent 3-row refugia strips comprised of Crimson clover and annual weeds. Beneficial arthropods monitored included the striped lynx spider, Oxyopes salticus, Crab spiders (Thomisidae), two big-eyed bugs, Geocoris punctipes and G. uliginosis, fire ants, Solenopsis invicta, the minute pirate bug, Orius insidiosus, an Anthicid (ant-like flower beetle), Notoxus monodon, three Coccinellids; Hippodamia convergens, Coccinella septempunctata, and Harmonia axyridis, a Nabid (Damsel bug) and a Chrysopid (Green lacewing). Pests monitored included the cotton aphid, Aphis gossypii, budworms, Heliothis virescens, bollworms, Helicoverpa zea, cabbage and soybean loopers, Trichoplusia ni and Pseudoplusia includens, thrips and the tarnished plant bug, Lygus lineolaris.

In Dooly county, the dominant generalist predators taken in Crimson clover sweep samples were O. insidiosus, spiders, Geocoris, and a Nabid. Crimson clover also harbors a diverse aphidophagous complex, including Coccinellids, several parasatoids, Syrphids and Chrysopids. Weather had a profound influence on beneficial and pest populations. 1995 was much drier than 1994, and overall densities of spiders, S. invicta, Coccinellids, lacewings, lepidopterous larvae, thrips and plant bugs were all significantly lower in both fields in 1995 than in 1994. Cotton aphid densities were seven times higher; Geocoris and Anthicid densities were not significantly different. Ratios of beneficials to lepidopterous larvae were significantly higher (p < 0.05) in the clover field. S. invicta was the only beneficial with significantly higher densities in the clover field during both seasons. S. invicta significantly reduced densities of Geocoris, Anthicids, Coccinellids and lacewings in the clover, but did significantly effect spiders.

In Tift county, seasonal densities of spiders, S. invicta, Geocoris and Coccinellids were significantly higher in cotton strips lying between or adjacent to the refugia strips than in cotton strips lying farthest from the refugia. Density and distribution of beneficials in the entire Tift county field remained high throughout the entire season.

A total of four foliar insecticide treatments were applied to the conservation-tilled field in Dooly county in 1994-95, vs. eight in the conventional-tilled field. No foliar insecticide treatments were applied in the Tift county cotton/refugia field.

Reprinted from Proceedings of the 1996 Beltwide Cotton Conferences pp. 1108 - 1114
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998