1. Progress in evaluating converted cotton race stocks for resistance to whiteflies and aphids Mary M. Toothaker Dr. Marvin Harris Dr. C. Wayne Smith Texas A&M University

2. Why is this necessary?  With the eradication of the boll weevil, secondary pests such as whiteflies and aphids have become important pests  Honeydew from excessive whitefly and aphid populations affect ginning and reduce quality of the fiber  Feeding by excessive populations of aphids and whiteflies can decrease nutrient availability (Photo: Richard Sequeira)

3.  Aphids and whiteflies are also known vectors of many plant viruses  Aphids becoming an increasing problem with use of Bt cotton  Aphid populations have been shown to be higher in Bt fields than non-Bt fields, probably because of a decreased use of insecticides Cotton Leaf Crumple Virus, transmitted by Bemisia tabaci

4. Selecting for Resistance  Research done in 2003 - 2004 confirmed that 6 cotton race stocks (CRS) out of a selection of 116 photoperiod-insensitive race stocks showed resistance to whitefly  TX0154  TX0156  TX0188  TX0195  TX0221  TX0242

5. Selecting for Resistance  TX0154 and TX0156 were shown to be significantly lower in percent survival  TX0188, TX0195, TX0221, TX0242 were shown to be significantly longer in developmental time

6. Selecting for Resistance  Goal: Do plants within one CRS show variability in resistance characteristics compared to a known susceptible  Selection criteria - whitefly survival and developmental time: Which is better?

7. Selecting for Resistance - Whitefly  4 plants of each CRS, 3 leaves per plant  Excised leaf technique  Ten adult whiteflies were placed and contained on each leaf

8. Selecting for Resistance - Whitefly  Whiteflies removed after 24 hours and clip cages placed on same area  Number of eggs laid were counted and recorded  Nymphs allowed to hatch and develop for 14 days  After 14 days, the number of each instar was counted every 24 hours until all had completed development or died  Mean number of days to adulthood and percent mortality were calculated for each plant within each race stock

11. Current Research  20 whole plants (6-8 leaf stage) of each CRS and a susceptible control (DP or PSC355)  Three cages per plant  7-8 adult whiteflies per cage

12. Results

15. Discussion  Mortality appears to be the better selection criteria  Much more variation within each CRS in percent mortality than the controls using excised leaf technique  Days to adulthood appear to be slightly higher in the test groups than the controls

16. Breeding  By using whole plants, individual plant selections (IPS) can be made within each CRS using this selection criteria

17. Other Projects  Use water-sensitive paper to measure honeydew production Quantify amount of honeydew produced per acre over time Could determine aphid numbers in a field by measuring the honeydew produced *in conjunction with USDA

18. Honeydew production by pecan aphid on a known susceptible variety of pecan Honeydew production on a suspected resistant variety of pecan Proof of Concept:

19. Acknowledgements  Cotton, Inc.  Texas A&M University – Department of Entomology Alexandra Gomezplata Jessica Honaker Robert Puckett Allen Dean Sarah Skrivanek  Texas A&M University – Plant Growth Facilities Roger Horn  Texas A&M University – Department of Soil & Crop Sciences Kasi Clay Dawn Deno  USDA-ARS-SPARC Dr. Juan Lopez Dr. Dan Martin