The effect of Brown marmorated stink bugs (Halyomorpha halys) on California Rice

Brown marmorated stink bug (BMSB) is an invasive stink bug from Asia that has been expanding through the United States since 1998. Many are concerned that the H. halys could be a threat to the California rice industry.  In 2013, Brown marmorated stink bug (Halyomorpha halys Stal) was found near Sacramento, at the southern edge of the Sacramento Valley where rice cultivation is prevalent. Two greenhouse studies conducted at UC Davis examined the effect of feeding by H. halys adults and nymphs on kernel weight at the milk, soft dough and hard dough stage of rice kernel development. Fecundity of these adults was also examined over the course of the study. The first experiment used only adults caged for a three weeks on developing panicles in October 2014.  Evidence from these studies show H. halys damages maturing rice kernels. Kernel weights were reduced in the presence of H. halys (F = 7.04, df = 1, 51, p = 0.0137) but not across kernel development stage. There was a significant interaction between the kernel development stage and presence of stink bugs, which revealed that damage was only significant during the milk stage (F = 14.65, df =1, 25 p = 0.007).  There were more aborted kernel on panicles that had been fed on during the milk stage. Kernels from the soft dough and hard dough stages that had been infested with stink bugs were more prone to rotting, breaking, and discoloration (F = 5.15, df = 2,25, p = 0.0134). In the second experiment, both adults and third-instar nymphs were used to infest rice panicles for one week on milk, soft, and hard dough stages in May 2015. We also tested the effect of silicon fertilization as part of an intial exploration into possible management tactics.  The data from the second experiment showed that the addition of silicon had not effect on kernel weights, but did increase the number of kernels on panicles (F = 4.90, df = 1,25, p = 0.0362). Kernels at the hard dough stage of development had heavier kernels than those at the milk stage as is expected because the kernels are being filled in at later stage (F = 3.73, df = 2, 25, p = 0.0382). The surprising and somewhat contradictory result is that panicles that were caged with adult and nymphs had heavier kernels than the control. The only significant difference in kernel weights was between panicles that had adults or nymphs (F  = 4.06, df = 2,51, p = 0.0232).  None of the interactions were significant, which could have helped explain some of the trends observed. However, the presence of stinkbugs seem to have increased the percentage of damaged kernels (F = 9.63, df = 2,51, p = 0.0003) and conversely the control had more clean kernels (F = 7.30, df = 2, 51, p = 0.0016). These results suggest that H. halys is a possible threat to rice production during the kernel maturation stages. However, a more complete study is needed to resolve the effects of difference of length of feeding times and possibly the effect of season.