Effects of the presence of barnyardgrass on rice water weevil (Coleoptera: Curculionidae) and rice stink bug (Hemiptera: Pentatomidae) populations on rice

Both the rice water weevil, Lissorhoptrus oryzophilus Kuschel, and rice stink bug, Oebalus pugnax (F.), are important pests of rice, Oryza sativa L., in the United States. The host ranges of both insects primarily consist of monocotyledonous plants. Previous research has shown that the rice water weevil prefers barnyardgrass, Echinochloa crus-galli Beauv., over rice for feeding and oviposition. Barnyardgrass is also a preferred host for rice stink bug. Thus, presence of barnyardgrass in rice fields may alter populations of one or both insects. Field experiments were conducted to determine how the presence of a preferred host influences rice water weevil and rice stink bug populations on rice. Mixed plots of barnyardgrass and rice were cultivated such that either rice was surrounded by barnyardgrass or barnyardgrass was surrounded by rice. Insects were collected from rice portions of mixed plots and compared with numbers collected from whole plots of rice in the same location. Presence of barnyardgrass had little impact on rice water weevil densities on rice. In contrast, presence of barnyardgrass influenced rice stink bug populations on rice. Rice stink bugs were found on barnyardgrass in mixed plots before panicle emergence of rice. After panicle emergence of rice, results varied from 2001 and 2002. In 2001 and 2003, rice stink bugs were up to 9 times more abundant on rice in mixed plots of barnyardgrass and rice compared with whole plots of rice. Rice stink bugs were up to 4 times greater on rice in whole plots of rice than in mixed plots in 2002. Differences are likely a result of the developmental stage of barnyardgrass relative to rice. Data suggest the presence and developmental stage of barnyardgrass can influence the severity and timing of rice stink bug infestations