Evaluation of mature soybean pods as a food source for two pod-sucking bugs, Riptortus pedestris (Hemiptera: Alydidae) and Halyomorpha halys (Hemiptera: Pentatomidae)

Riptortus pedestris (Fabricius) and Halyomorpha halys (Stal) cause injury to soybeans by piercing and sucking pods and seeds. Growers believe that new damage decreases near to harvest despite the occurrence of these bugs at that time. As this question has never been assessed, we evaluated two diets: a) mature soybean pods (dried shell + dried soybean seeds) and b) dried soybean seeds for the two bugs by assessing their biological, behavioral, and morphological attributes on each diet in laboratory. While nymphs of both species were able to develop and adults able to reproduce on the tested diets, bugs fed on pods had longer development times and 2.2 to 5.0 times higher mortality rates than bugs fed on seeds. Furthermore, adult longevity of R. pedestris and H. halys fed on pods was 8.4 and 7.5 days shorter, respectively, than that of bugs fed on seeds. However, pod feeding had no effect on adult fecundity or egg viability. In a behavioral choice test, adult R. pedestris preferred seeds over pods and probed seeds longer than pods. On average, adult H. halys also preferred seeds over pods, although 15.6% of H. halys showed the reverse, preferring pods over seeds. The proboscis length and estimated depth of stylet penetration into the host tissue of both nymphs and adults of both species was much greater than the thickness of the pod shell, suggesting that mouthpart structure does not explain the negative effects of pods vs. seeds. In conclusion, mature soybean pods were found to be a suitable food source for both R. pedestris and H. halys despite some negative effects, and thus careful attention should be paid to the population levels of these two bugs approaching harvest to reduce economic damage in soybean.