Changes in nutritional composition of soybean seed caused by feeding of pentatomid (Hemiptera: Pentatomidae) and alydid bugs (Hemiptera: Alydidae).

Changes in protein, lipid, and carbohydrate content, and the weight loss of soybean seeds caused by the feeding of 6- to 7-d-old unmated male adults of the pentatomids Peizodorous hybneri (Gmelin) and Halymorpha halys (Stål), and an alydid, Riptortus pedestris (F.), were examined in the laboratory. Our goals were to determine which species had the greatest capacity to damage soybean seed and to measure the effect of that damage on the nutritional composition of soybean seed. Individuals of the three species were provided with a preweighed dry soybean seed and allowed to feed for 0, 4, 8, 12, 16, 20, and 24 d, after which the remaining seed was analyzed for any change in weight, protein, lipid, and carbohydrate concentration. Lipids, carbohydrates, and seed weights were reduced by bug feeding, and the reduction was directly proportional to feeding duration. H. halys was found to be the most voracious feeder, reducing soybean seed weight by 42% after 24 d of feeding. There was a significant interaction between species and feeding duration for changes in nutritional components. Seeds fed on by H. halys had the highest incremental increase in protein content (13%) after 24 d of feeding, followed by those fed on by R. pedestris and P. hybneri. However, carbohydrates and lipid content of the soybean seeds fed by the tested insect species were found to decrease significantly. Soybean pods at mature stages remain in the field for a long period, and findings of our study suggest that longer exposure of the mature soybean pods to these pest species in the field may lead to low-quality seeds and lower yields, and may even affect the germination potential of the seeds.

Effect of aggregation pheromone trap of Riptortus pedestris (Hemiptera: Alydidae) on the distribution and composition of its egg parasitoids.

The aggregation pheromone of Riptortus pedestris (F.) (Hemiptera: Alydidae) is known to attract its egg parasitoids Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) and Gryon japonicum (Ashmead) (Hymenoptera: Scelionidae). Distribution and composition of these egg parasitoids were compared in a soybean field in the presence and absence of aggregation pheromone-baited traps for two consecutive years. Three traps were installed on the edge of a soybean field, first without and then with aggregation pheromone in a before-after design, and changes in parasitism were assessed on nonviable host eggs released at distances of 9, 18, 27, and 36 m from the trap. A significant interactive effect of pheromone installation and distance was found in egg parasitism by both parasitoids. Parasitism on eggs recovered from 9 m away was up to 2.2 and 3.2 times higher in presence of pheromone than without pheromone for O. nezarae and G. japonicum, respectively. Parasitism by O. nezarae was always higher than that by G. japonicum, but their relative abundance, clutch size, and sex ratio were not affected by pheromone installation, irrespective of distance from the trap. In conclusion, aggregation pheromone increases abundance of parasitoids up to 18 m from trap installation points and does not affect the relative abundance of parasitoid species.