Testing for imidacloprid resistance in blackmargined aphid (Monellia caryella) poulations from Texas pecan orchards

During 2011 and 2012 a total of 46 separate laboratory tests of blackmargined pecan aphids, BMA from orchards across 11 Texas counties were tested against imidacloprid. All testing was conducted in a laboratory setting by placing BMA alates on treated foliage and recoding mortality and first instar production at 24, 48 and 72 hours. Results after 72 hours of continuous exposure to imidacloprid treated foliage ranged from 85 percent survival and 165 first instars produced to zero percent survival with no first instars.  This range of control showed that there are areas of resistance in Texas. When difficult to control populations were retested against products with a different mode of action (IRAC Groups 4C, sulfoxaflor;  Group 9B, pymetrozine and Group 9C, flonicamid) effective control was achieved. Where imidacloprid was effective against blackmargined aphid populations, effective control was also achieved by another IRAC Group 4A insecticide – clothianidin. Based on two years of test results, recommendations for management actions to reduce or prevent resistance to imidacloprid in BMA populations include:

• Rotate IRAC group numbered products, not name brands
• Do not use more than two consecutive applications of  the same IRAC group numbered product
• Where possible treat only problem varieties or areas
• Do not base your treatment decision just on the presence of honeydew