Impact of selected insecticides on Lygus lineolaris and beneficial arthropods associated with cotton

Production of cotton, an important commodity in the United States, provides numerous jobs, as well as fiber, oil, and cottonseed meal for feed. In 1994, 234,000 hectares of cotton were harvested in Tennessee, contributing approximately $227,448,000 to the state's economy.

Cotton, a plant native to the West Indies, was introduced into the United States during colonial times. Some pests of cotton have been imported on other plants, while others use cotton as an alternate host, such as Lygus lineolaris, the tarnished plant bug (TPS), which damages cotton bolls and causes significant yield reductions.

Reliance on chemical methods to control pests of cotton has led to problems with integrating other management strategies and reducing selection pressures. Knowledge of the insecticide and its impact on the pest species and beneficial arthropods is essential to selecting and implementing pest management programs.

Because of the importance of cotton to the nation's economy, and because of the impact of pests, it is necessary to utilize efficient means of control for these pests. Research was conducted at the West Tennessee Experiment Station in 1993 and 1994 to evaluate the impact of selected insecticides on TPB. The objectives of this research were to: 1) determine the impact of recommended insecticides on TPB in field cage tests, 2) determine the effects of selected early-season Insecticides on beneficial arthropod populations, and 3) evaluate the resistance of TPB to selected insecticides in West Tennessee.

Efficacy tests showed that acephate, dicrotophos, malathion, and oxamyl consistently provided initial and residual control of TPB with lower rates of acephate, dicrotophos, and malathion achieving percent mortalities not significantly different from recommended rates. Azinphosmethyl and dimethoate, when used in combination, provided higher mortalities than when each was applied alone.

Insecticides applied for management of an insect pest may cause outbreaks of secondary pests, resurgences of primary pests, and/or reduce the survivorship of beneficial arthropods that are necessary for pest control. Insecticides that are commonly applied early-season for TPB management did cause reductions in beneficial arthropod densities at 1 and 3 days after treatment; however, overall densities showed an increase by 7 days after treatment.

Until recently, pest management included multiple applications of broadspectrum insecticides. This philosophy led to insecticide resistance in many key pests. Increased pest resistance limits the effectiveness of many pesticides. Resistance studies performed in low, medium, and high cotton-producing sites in West Tennessee provided base-line information necessary for future determinations of LC₅₀ values. The range of concentrations tested produced LC₅₀ values for acephate and malathion. These values show that selection pressures are present In West Tennessee.

Insecticides are valuable tools in pest management. By monitoring the efficacy and resistance status of an insecticide, effective management practices can be employed. From this research, acephate and malathion can be used to achieve high levels of mortality; however, the possible development of resistance to these insecticides in areas of West Tennessee exists. This research suggests that early-season pests, such as TPB, can be managed using pesticides without harming beneficial arthropod populations that aid in late-season pest control. This type of information regarding insecticides depended upon for pest management supports incorporation of chemical control methods into integrated management programs.