Farmscape Ecology of Stink Bugs in Northern California

Abstract

<i>A complex of stink bugs causes sporadic damage to row crops such as tomato, dried bean, and bell pepper in northern California. This complex consists of five species: consperse stink bug</i>, Euschistus conspersus <i>Uhler; redshouldered stink bug</i>, Thyanta pallidovirens <i>(Stål); southern green stink bug</i>, Nezara viridula <i>(L.); Uhler’s stink bug</i>, Chlorochroa uhleri <i>(Stål); and conchuela stink bug</i>, C. ligata <i>(Say). Laboratory studies revealed that green tomato fruit was a relatively poor host for some of these bugs, compared with green-bean pods. The egg-parasite guild associated with the complex consists of 11 species</i>: Anastatus pearsalli <i>Ashmead (Eupelmidae)</i>; Ooencyrtus californxicus <i>Girault and</i> O. johnsoni <i>(Howard) (Encyrtidae); and</i> Gryon obesum <i>Masner</i>, Telenomus podisi <i>Ashmead</i>, Psix tunetanus <i>(Mineo &amp; Szabo)</i>. Trissolcus euschisti <i>(Ashmead)</i>, T. hullensis <i>(Harrington)</i>, T. utahensis <i>(Ashmead)</i>, T. cosmopeplae <i>(Gahan), and</i> T. basalis <i>(Wollaston) (Scelionidae). In laboratory no-choice tests, most insect predators did not feed on eggs of E.</i> conspersus, <i>whereas most fed extensively on 2nd instars</i>. <i>A 3-yr study of stink bugs and their egg parasites/predators was conducted at a northern California farmscape consisting of agricultural land (planted primarily to processing tomato), and adjacent riparian and road side vegetation. Stink bugs overwintered as diapausing adults in the riparian habitat. In riparian vegetation (primarily blackberry</i>, Rubus <i>spp.), predation on sentinel egg masses by Argentine ant</i>, Linepithema humile <i>(Mayr), was a major mortality factor for all species but</i> N. viridula; <i>four egg parasites were recovered, but rates of parasitization of sentinel egg masses were relatively low. There was no evidence of stink bug reproduction in blackberry. The first generation of stink bugs developed in the spring on roadside weeds (primarily Brassicaceae); predation by Argentine ant and common pillbug</i>, Armadillidium vulgare <i>(Latreille), on sentinel egg masses in weedy vegetation was relatively high for all species except</i> N. viridula. <i>Eggs of the latter species appeared to be distasteful to these predators; however, predation on</i> N. viridula <i>eggs by mice (probably</i> Mus musculus <i>L.) was relatively high in weedy vegetation. Eggs of E</i>. conspersus <i>that were parasitized by either</i> O. californicus <i>or</i> T. basalis, <i>and eggs of</i> N. viridula <i>that were parasitized by</i> T. basalis <i>were preyed upon at rates comparable to nonparasitized eggs (i.e., intraguild predation). Very few egg parasites were recovered from the weedy vegetation. The second generation of stink bugs developed in the adjacent tomato field;</i> E. conspersus <i>was the dominant species. Predation on sentinel egg masses in tomato was generally insignificant. Common pillbug was not abundant and Argentine ant did not colonize the field. Those invertebrate predators that did colonize the field did not exploit sentinel egg masses to any extent. Seven species of parasites were reared from sentinel egg masses in tomato, and total percentage parasitization was relatively high on some sample dates</i>. <i>The results suggest that predation on stink bug eggs during the first generation is a major mortality factor. Because of this intense predation, the pool of surviving adults that is available to colonize the adjacent tomato field is greatly reduced. However, this predation pressure (including intraguild predation) also prevents the buildup of egg parasites that would otherwise colonize the tomato crop. As a result, stink bug populations may exceed the established treatment threshold. For management of</i> E. conspersus, <i>several tactics should be explored at similar farmscapes in northern California, including pheromone trap-out of adults in early spring, manipulation of riparian and roadside vegetation, conservation of egg parasites and nymphal predators, and augmentative release of egg parasites. It is suggested that an understanding of the ecology of stink bugs and their major natural enemies at the farmscape level should improve our ability to devise ecologically based management systems for these pests</i>.