Submitted to: Journal of Economic Entomology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/1/2003
Publication Date: 6/1/2003
Citation: Snodgrass, G.L., Scott, W.P. 2003. Effect of ulv malathion use in boll weevil (coleoptera: curculionidae) eradication on resistance in the tarnished plant bug (heteroptera: miridae). Journal of Economic Entomology. Interpretive Summary: Boll weevil eradication is currently being conducted in many cotton growing regions in the southeastern and southwestern United States. Eradication is accomplished by use of ULV (ultra-low volume) malathion applications to cotton grown in the eradication areas. In the first year of eradication a reproduction-diapause control program is used in which multiple ULV malathion applications (typically ten) are made to cotton from August through early-September. These applications along with those made in following years place a selection pressure on tarnished plant bugs, another pest of cotton, to develop resistance to malathion. We studied the development of resistance to malathion in plant bug populations in areas of the Mississippi River Delta undergoing boll weevil eradication from 1999-2001. Resistance levels were determined using a glass-vial bioassay. Tarnished plant bugs were collected from weeds near cotton in the spring (before cotton was fruiting) and again in the fall (when the cotton was mature) at eleven locations and tested for resistance to malathion. The same collection locations were used each year. We found that resistance to malathion in many plant bug populations increased from spring to fall with increases in resistance as high as 30-fold as compared to susceptible plant bugs. Fortunately, at most locations the resistance found in the spring was significantly lower as compared to the resistance found the previous fall. Thus, the increases in malathion resistance did not appear to be stable in the populations and were rapidly lost during the fall, winter, and spring. However, one population did overwinter with a fairly high level of resistance in one year. This means that growers in eradication areas should not assume that the ULV malathion applications made for boll weevil control will also control plant bugs in the field, since it is possible for plant bugs with malathion resistance to be present when fruiting begins. Use of ULV malathion for early season boll weevil control in such fields will only increase malathion resistance in the plant bugs. Fields in which ULV malathion is used should be checked regularly for plant bugs and treated with a different insecticide if needed.
Technical Abstract: Tarnished plant bugs, Lygus lineolaris (Palisot de Beauvois), from Regions 1 (north Delta), 2 (south Delta), and 3 (hills) of the boll weevil, Anthonomous grandis Boheman, eradication program in Mississippi were collected from wild hosts and tested for malathion resistance in the fall of 1999 and during the spring and fall of 2000 and 2001. In Region 1, tarnished plant bugs also were tested in late July of 1999, just prior to the start of the multiple applications of ULV (ultra-low volume) malathion used for reproduction-diapause control of boll weevils in August. A glass-vial bioassay was used to determine resistance in plant bugs to malathion, and LC50 values obtained were compared to an LC50 value obtained for susceptible plant bugs from Crossett, AR. Comparison of the LC50 value obtained for plant bugs at a location in the spring also was made to the LC50 value obtained in the fall at the same location. Applications of malathion made for reproduction-diapause boll weevil control increased malathion resistance in plant bugs from July of 1999 to October of 1999 by 4.9-, 6.5-, and 20.8-fold at the three locations in Washington County where plant bugs were tested in Region 1. Results from testing bugs from all three eradication regions were similar. Malathion resistance usually increased significantly from spring to fall, then declined significantly from fall to spring of the next year. Despite greatly reduced use of malathion in all three eradication regions for boll weevils in 2001 (due in part to a cold winter in 2000-2001), resistance to malathion in plant bugs still increased significantly from spring to fall at all test locations in Regions 1 and 2 (the Delta). The increase in malathion resistance from spring to fall in Regions 1 and 2 in 2001 is thought to be the result of extensive use of organophosphate insecticides for plant bug control in cotton in the Delta in 2001. Plant bugs were a minor problem in cotton in Region 3 (the hills) in 2001, and malathion resistance did not increase significantly in plant bug populations from spring to fall at three of four test locations in this year. Overall test results showed that the use of malathion in boll weevil eradication can rapidly produce several fold increases in resistance to malathion in plant bug populations. However, in most cases the expression of this resistance was rapidly lost. The reason(s) for the loss of resistance is unknown.