Beneficial and Pest Insect Populations in Conventional and Organic Cotton, and Organic Cotton with Habitat

Abstract

A field study was conducted in 2004 and 2005 to compare pest and beneficial insect populations in conventional and organic cotton (Gossypium hirsutum L.), and organic cotton with managed habitat. A "conventional" (best management practices) control was compared with two organic treatments - one with and one without habitat borders. The habitat treatment consisted of an organic cotton plot bordered and bisected by a 3 m wide mixed planting of soybean (Glycine max), German foxtail millet (Setaria italica), and buckwheat (Fagopyrum esculentum Moench).

Pest and beneficial insect populations were monitored by methods appropriate to the developmental stage of the cotton and pest species populations. Thrips were sampled beginning at cotyledonary stage and were sampled on four dates each in 2004 and 2005. Weekly sweep net samples were taken to monitor pest and beneficial insect populations on eight dates in 2004 and ten dates in 2005. Pest insects recorded included adults and immatures of green stink bug Acrosternum hilare (Say), Southern green stink bug Nezara viridula (Linnaeus), brown stink bug Euschistus servus (Say), tarnished plant bug Lygus lineolaris (Palisot de Beauvois) and bollworm Helicoverpa zea. Predatory species recorded were adult Dolichopodidae, larvae of Corydalidae and Hemerobiidae, spiders, adults and immatures of Orius spp., Geocoris spp., predatory Coccinellidae, and Nabidae. Observation of the fate of naturally oviposited H. zea eggs was used as a measure of egg parasitism and predation. The level of parasitism of brown stink bug (Euschistus servus) eggs was evaluated by gluing E. servus egg masses to cotton leaves in the field and recording levels of parasitism. Cotton terminals, squares, and bolls were monitored for H. zea eggs, larvae, and damage. Internal damage to cotton bolls by hemipteran pests was recorded. Organic or conventional insecticides were applied if necessary for control of key cotton pests.

Orius spp. means were significantly higher in the organic treatment than the conventional control. Lady beetles and L. lineolaris means, averaged over both years, were significantly higher in both organic treatments than the conventional control. There was no treatment effect in predator plot means in the pitfall study or in levels of H. zea egg predation and parasitism in the H. zea egg fate study. There was no treatment effect in the level of E. servus egg parasitism. H. zea larvae and H. zea-damaged bolls were higher in both organic treatments than conventional cotton. Damage to bolls by hemipteran pests was higher in both organic treatments than the conventional control.

Organic cotton had higher densities of two predators: lady beetles and Orius spp. However, organic cotton had more damage from pests. Presence of habitat did not increase the number of beneficial insects, decrease the number of pests, or reduce damage in adjacent cotton.