MONITORING CYPERMETHRIN SUSCEPTIBILITY IN LOUISIANA BOLLWORM DURING 2004-2005.

The susceptibility of over 2,000 bollworm moths to pyrethroids was determined using the adult vial test (AVT) from May to Sep during 2004 and 2005. In 2004, survival at 5 μg/vial during May, Jun, Jul, Aug, and Sep was 9%, 16%, 30%, 21%, and 30%, respectively, with a mean survival of 23%. In 2005, survival at 5 μg/vial during May, Jun, Jul, Aug, and Sep was 23%, 34%, 43%, 43%, and 38%, respectively, with a mean survival of 38%. Bollworm survival during 2005 was at the highest level recorded in Louisiana. Mean annual survival of bollworm exposed to 10 μg/vial for 2004 and 2005 was 12% and 22%, respectively. In 2004, LD₅₀'s of bollworm larvae from field colonies collected at St. Joseph, Bossier, and Winnsboro in topical bioassays were 1.28, 3.24, and 6.12 μg/g, respectively. The Winnsboro colony tested in 2004 had a resistance ratio that was 7 to 22 fold higher than the pyrethroid-susceptible colonies tested during 1998. In 2005, LD₅₀'s of colonies from Somerset, St. Joseph, Sicily Island, St. Francisville, and Winnsboro were 0.68, 2.04, 2.04, 2.20, and 3.48 μg/g, respectively. Although these data clearly show bollworms are becoming less susceptible to pyrethroids in laboratory tests, no field control failures of bollworms with pyrethroids have been reported in Louisiana to date. [ABSTRACT FROM AUTHOR]