Phosphine resistance in eggs of Tribolium castaneum and Plodia interpunctella from almond storage facilities in the Central Valley of California
Abstract: Phosphine (PH3) is heavily relied upon for stored-product pest management worldwide. Several studies have revealed high frequencies of PH3 resistance in stored-product insects in many countries including the United States. These studies focused on adults, usually the most fumigant-susceptible life stage. In this study, we established discriminating doses of PH3 for Tribolium castaneum (red flour beetle, RFB) and Plodia interpunctella (Indian meal moth, IMM) eggs using laboratory susceptible strains for detection of resistance in eggs, the most fumigant-tolerant life stage. The discriminating doses for RFB and IMM eggs were established based on 3-d fumigation and were 73.6 and 109.8 ppm, respectively. Discriminating dose tests showed that eggs of four out of 11 RFB field populations collected from almond storage facilities in California had resistance frequencies (percentage survival) that ranged from 54-100%. All IMM populations tested were resistant to PH3 and resistance frequencies ranged from 4-20%. Based on 3-d fumigation, dose-response tests and probit analyses determined that LC99 (concentration required to kill 99% of the eggs) values for susceptible and the most resistant RFBeggs were 50.8 and 653.9 ppm, respectively. Resistance frequencies and levels of resistance in different life stages of RFB and IMM and their implications for resistance management are discussed.