Susceptibility of Rice to Oebalus pugnax (F.) (Hemiptera: Pentatomidae) Feeding at Different Levels of Grain Maturity and Impacts on Insecticide Termination.

The stages of rice, Oryza sativa L. (Poales: Poaceae), grain maturity that are most susceptible to rice stink bug, Oebalus pugnax (F.), damage have been identified; however, the stage at which they are no longer capable of causing appreciable damage during grain maturity is unclear. The objective of this study was to determine the susceptibility of rice to rice stink bug feeding at different levels of grain maturity and determine an insecticide termination timing. Rice stink bug damage was examined using five levels of grain maturity described as percent of kernels reaching mature straw coloration referred to as hard dough (20, 40, 60, 80, and 100%) across a range of infestation levels using single panicle sleeve cages and large cages. Hybrid and conventional cultivar rice panicles at 20, 40, and 60% hard dough were found to be susceptible to indirect yield loss, as two rice stink bugs per panicle resulted in over 7% peck. In large cage trials, 25 rice stink bugs caused 0.7-1% peck to hybrid and conventional rice plots at 20% hard dough. Much less damage was observed once rice reached 60% hard dough, where peck averages only reached 0.4%. Decreased damage at 60% hard dough was validated using uncaged trials where 0.4% additional peck was observed in unsprayed plots. These data indicate that rice in the early stages of hard dough is susceptible to large levels of indirect yield loss, but unless significant densities of rice stink bug are present at 60% hard dough, no more sampling or applications are necessary.

Geographic Variation in Phosphine Resistance Among North American Populations of the Red Flour Beetle (Coleoptera: Tenebrionidae).

The red flour beetle, Tribolium castaneum (Herbst), is a common stored-product pest found worldwide. Phosphine, hydrogen phosphide (PH3), is the most commonly used fumigant for stored grains, for which genetically based resistance has been recorded for several pest species. This study assessed phosphine resistance in 25 T. castaneum populations from across the United States and Canada using a discriminating dose bioassay. Dose-mortality assays were conducted with adults from seven of these populations to categorize weak and strong resistance phenotypes. Phosphine resistance was detected in 12 out of the 25 populations, and the frequency of resistance within populations varied from 2% in Victoria, TX, to 100% in Red Level, AL. Two resistant populations from Kansas that had been sampled three years earlier were found to have similar resistance frequencies in the current study. None of the four Canadian populations had any detectable resistance among the insects tested. Resistance ratio calculations from LC50 value in resistant populations relative to the LC50 for the laboratory susceptible strain allowed resistance phenotypes to be assigned as either weak resistance, at 5- to 26-fold resistance relative to susceptible, or strong resistance at 95- to 127-fold relative to susceptible. This study suggests that proper resistance assessment techniques can help to determine occurrence of phosphine resistance in populations of T. castaneum and can further characterize the strength of resistance present. These data can be used to support resistance management programs that consider either cessation or modification of phosphine fumigation to control T. castaneum.