5. LC50 VALUES
Amount of insecticide (in micrograms) needed to kill 50% of the plant bugs exposed to it. Requires 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.

6. 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.

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

8. 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

9. Mean % Mortality Discriminating - Dose Permethrin
(15 µg for 3 hours, 20 Delta, 10 Hill Locations)
Susceptible 90% or > Mortality

10. (20 Delta, 10 Hill Locations Aug. – Sept.)
Orthene Mean LC50
Hills May ’06 – 8.4
Delta May ’06 – 8.5
Susceptible LC50 – 3.1

11. MULTIPLE INSECTICIDE RESISTANCE
Rolling Fork, MS - Fall Bruce, MS - Fall 2005
LC RR LC RR
Permethrin Permethrin
Malathion Malathion
Bidrin Bidrin
Orthene Orthene
Vydate Vydate <1
Imidicloprid

12. 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.

13. ADULTS FROM ROLLING FORK
Treatment Mean % mortality 48 h
Check
Orthene (0.5)
Orthene (1.0)
Bidrin (0.5)
Baythroid (0.033)
Vydate (0.33)
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

14. FIELD TEST SEPTEMBER 2006 Treatment Mean % mortality 48 h
Vance Stoneville
Check
Orthene
Orthene
Bidrin
Centric 2 oz
Vance LC50 for Orthene = 22.1 µg/vial RR = 7.1

15. Location LC50 (µg/vial) 2005 LC50 (µg/vial) 2006 Change
RESULTS IMIDICLOPRID (TRIMAX) RESISTANCE SURVEY
Location LC50 (µg/vial) LC50 (µg/vial) Change
Crossett, AR
Indianola, MS
Hollandale, MS * +4.15
Clarksdale, MS * +4.59
Mound Bayou, MS
Merigold, MS * +2.93
Greenville, MS
Greenwood, MS
Rolling Fork, MS
Tunica, MS * +1.24
Drew, MS * +2.70
Lambert, MS * +1.47
Oak Grove, LA * +0.74
McGhee, AR * +1.56
Lake Village, AR * +2.93
Mean
(2.7-fold)

16. CENTRIC BIOASSAYS SEPT. - OCT 2006
Location LC50 by contact LC50 by ingestion (24 h)
Crossett (susceptible)
Vance *
Rolling Fork *
Leland *
Clarksdale
Merigold
Hollandale *
Winterville *
Avon
Indianola
Mean
LC50 values are in micrograms per vial.