LC50 VALUES Amount of insecticide (in micrograms) needed to kill 50% of the plant bugs exposed to it. Requires 150 - 300 adults and a 24 h exposure period. Allows for comparison of populations in different locations and in time. Used to compute resistance ratios (RR): RR = LC50 of test population LC50 of a susceptible population The higher the RR the greater the amount of resistance. The RR at which control problems occur must be estimated with field or spray table tests.

DISCRIMINATING-DOSE Amount of insecticide (in micrograms) that will kill 90% or > of the susceptible bugs exposed to it in a short (2 or 3 h) period of time. Requires a minimum of 50 bugs. Results are in % mortality and mortalities less than 90% indicate tolerance or resistance is present. The % mortality at which control problems occur must be estimated with field or spray table tests.

DISCRIMINATING-DOSE TESTS FOR PLANT BUGS Pyrethroids - 15 ug of permethrin for 3 h

COLLECTION LOCATIONS Delta, MS Delta, AR Delta, LA Hills, MS Avon Lake Village Lake Providence Bruce Greenville Grady Translvania Winona Rolling Fork Gould Elliott Clarksdale Parkdale Gore Springs Minter City Bradford Ruleville Coffeeville Marks Oxford Tunica Charleston Indianola Water Valley Grady Batesville Vicksburg Winterville Thornton Greenwood

Mean % Mortality Discriminating - Dose Permethrin (15 µg for 3 hours, 20 Delta, 10 Hill Locations) Susceptible 90% or > Mortality 00 01 02 03 04 05 06 07

(20 Delta, 10 Hill Locations Aug. – Sept.) Orthene Mean LC50 Hills May ’06 – 8.4 Delta May ’06 – 8.5 Susceptible LC50 – 3.1 98 99 00 01 02 03 04 05 06 07

MULTIPLE INSECTICIDE RESISTANCE Rolling Fork, MS - Fall 2005 Bruce, MS - Fall 2005 LC50 RR LC50 RR Permethrin 62.2 18 Permethrin 33.7 10 Malathion 74.5 21 Malathion 81.5 23 Bidrin 7.1 7 Bidrin 3.4 3 Orthene 11.1 3.6 Orthene 9.91 3.2 Vydate 58.9 4.8 Vydate 7.54 <1 Imidicloprid 1.21 1.4

FIELD TESTS 2005 Adults were collected from pigweed near cotton in late-August and September 2005 at Rolling Fork. They were tested in cotton at Stoneville by caging them on terminals of cotton treated with formulated insecticides. There were 2 adults per cage, 10 cages per replication, with 4 replications of each treatment.

ADULTS FROM ROLLING FORK Treatment Mean % mortality 48 h Check 8 Orthene (0.5) 39 Orthene (1.0) 48 Bidrin (0.5) 44 Baythroid (0.033) 25 Vydate (0.33) 20 LC50 Permethrin 62.2, RR = 18 LC50 Orthene 11.1, RR = 3.6 LC50 Vydate 58.9, RR = 4.8 LC50 Bidrin 7.1, RR = 7

FIELD TEST SEPTEMBER 2006 Treatment Mean % mortality 48 h Vance Stoneville Check 5 13 Orthene 0.5 33 74 Orthene 1.0 23 85 Bidrin 0.5 88 98 Centric 2 oz. 95 97 Vance LC50 for Orthene = 22.1 µg/vial RR = 7.1

Location LC50 (µg/vial) 2005 LC50 (µg/vial) 2006 Change RESULTS IMIDICLOPRID (TRIMAX) RESISTANCE SURVEY Location LC50 (µg/vial) 2005 LC50 (µg/vial) 2006 Change Crossett, AR 0.85 ------ ------- Indianola, MS 2.16 2.24 +0.08 Hollandale, MS 0.98 5.13* +4.15 Clarksdale, MS 1.89 6.48* +4.59 Mound Bayou, MS 0.64 1.96 +1.32 Merigold, MS 1.18 4.11* +2.93 Greenville, MS 0.81 1.62 +0.81 Greenwood, MS 0.48 1.48 +1.00 Rolling Fork, MS 1.87 2.74 +0.87 Tunica, MS 1.42 2.66* +1.24 Drew, MS 0.64 3.34* +2.70 Lambert, MS 0.45 1.92* +1.47 Oak Grove, LA 0.99 1.73* +0.74 McGhee, AR 0.95 2.51* +1.56 Lake Village, AR 0.55 3.48* +2.93 Mean 1.10 2.96 +1.86 (2.7-fold)

CENTRIC BIOASSAYS SEPT. - OCT 2006 Location LC50 by contact LC50 by ingestion (24 h) Crossett (susceptible) 5.8 1.4 Vance 33.9* 1.7 Rolling Fork 18.2* 1.6 Leland 16.8* 2.2 Clarksdale 9.5 0.6 Merigold 9.0 1.1 Hollandale 12.8* 2.3 Winterville 19.6* 1.7 Avon 5.2 0.4 Indianola 8.6 1.8 Mean 14.8 1.5 LC50 values are in micrograms per vial.