Males of Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae), the lesser grain borer, produce the aggregation pheromones dominicalure-1 (DL-1) and dominicalure-2 (DL-2), which attract conspecifics for mating and to food sources. Pheromone emissions by single males feeding on 10 different plant-based diets were analyzed in a laboratory study by gas chromatography to compare effects of different host plants on pheromone emission. Body size measurements also were made from individual male R. dominica feeding on a single host to investigate variation in pheromone output and to determine the relationship, if any, between body size and pheromone output in the species. Hosts on which larvae were reared did not affect pheromone output, but hosts on which adult males fed had significant effects. Mean total pheromones (DL-1 DL-2) released by male R. dominica confined on wheat seeds for 24 h was 1,060 ng at 20 d old. There was a significant reduction in mean total pheromones (DL-1 DL-2) output from 1,246 ng when males were fed on seeds, especially cereal grains, to 60 ng when fed on woody tissues such as elm twigs. In treatments in which pheromone release was low, beetles released similar amounts of DL-1 and DL-2, whereas when pheromone output was high they tended to produce more DL-1 than DL-2. Similarly, when a significant difference between quantities of DL-1 and DL-2 was observed, more DL-1 was emitted. There were no interactions between output of either of the two pheromones, DL-1 or DL-2, and adult food sources. Percentages of DL-1 in quantities of DL-1 DL-2 emitted ranged from 41 to 61% and averaged 51%. Percentages of DL-1 in DL-1 DL-2 released by males fed test foods were not significantly different from the control (wheat) in ≈78% of the cases; in cases for which a significant difference from the control was observed, the ratio of pheromones released shifted from a DL-1 skewed output to equivalent amounts of the two pheromones. Regression analyses indicated no significant relationship between either total body length, pronotal width, or fresh body weight, and of pheromone measurements: quantity of DL-1 or DL-2 individually, total quantity of DL-1 and DL-2, or the percentage of DL-1 in the pheromone blends.
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Vol. 100 • No. 1