• Pro-active Management of Beet Armyworm (Spodoptera exigua) Resistance to IGRs, Tebufenozide and Methoxyfenozide

      Moulton, John K.; Pepper, David A.; Dennehy, Timothy J.; Byrne, David N.; Baciewicz, Patti; Extension Arthropod Resistance Management Laboratory, Department of Entomology (College of Agriculture, University of Arizona (Tucson, AZ), 2000-08)
      Susceptibility to tebufenozide and methoxyfenozide of beet armyworm (Spodoptera exigua) from the southern United States and Thailand was determined through exposure of first and third instar larvae to dipped cotton leaves. LC50 estimates of first instar larvae ranged from 0.377 to 32.7 micrograms of tebufenozide per milliliter and 0.034 to 11.5 micrograms of methoxyfenozide per milliliter. LC₅₀ estimates of third instar larvae ranged from 4.37 to 715 micrograms of tebufenozide per milliliter and 0.393 to 47.4 micrograms of methoxyfenozide per milliliter. These estimates translated into 87-fold and 164-fold decreases in susceptibility to tebufenozide and 338-fold and 121-fold decreases in susceptibility to methoxyfenozide of first and third instar larvae from a Thailand strain when compared to the most susceptible of eight United States populations evaluated. Among the United States field populations evaluated, a collection from Belle Glade, Florida was the most susceptible and one taken near Parker, Arizona was the least susceptible. Selection of the Thailand population with tebufenozide or methoxyfenozide resulted in significant reductions in susceptibility to both analogs, indicating a common mechanism of resistance. Isolation and characterization of resistance will provide information that will be helpful for pro-active management of resistance for this valuable group of insecticides in the United States.
    • Susceptibility of Arizona Whiteflies to Neonicotinoid Insecticides and IGRs: New Developments in the 1999 Season

      Li, Yongsheng; Dennehy, Timothy J.; Li, Xiaohua; Wigert, Monika E.; Byrne, David N.; Baciewicz, Patti; Extension Arthropod Resistance Management Laboratory, Department of Entomology (College of Agriculture, University of Arizona (Tucson, AZ), 2000-08)
      Whiteflies are serious pests of cotton, melons, and winter vegetables in Arizona’s low deserts. Successful management of whiteflies requires an integrated approach, a critical element of which is routine pest monitoring. In this paper we report findings of our 1999 investigations of resistance of Arizona whiteflies to insect growth regulators (IGRs) and neonicotinoid insecticides. Whiteflies collected from cotton fields, melon fields and greenhouses were tested for susceptibility to imidacloprid (Admire /Provado), and two other neonicotinoid insecticides, acetamiprid and thiamethoxam, and to two insect growth regulators (IGRs), buprofezin (Applaud ) and pyriproxyfen (Knack ). Contrasts of 1999 and 1998 results indicated increased susceptibilities, on average, to both imidacloprid and buprofezin of whiteflies collected from cotton. A cropping system study showed that whiteflies collected from spring melons had significantly lower susceptibility to imidacloprid than those collected from cotton or fall melons. The opposite was found for pyriproxyfen, to which whiteflies from cotton and fall melons had lower susceptibility than those from spring melons. As in 1998, whiteflies with reduced susceptibility to imidacloprid continue to be found in certain locations, particularly in spring melon fields and greenhouses. Results of our laboratory bioassays on susceptibility of Arizona whiteflies to neonicotinoid insecticides provided evidence of a low order cross-resistance between imidacloprid, acetamiprid and thiamethoxam. Monitoring in 1999 provided the first evidence of reduced susceptibility of Arizona whiteflies to pyriproxyfen.