First Report of a Mermithid Nematode InfectingPiezodorus guildiniiandAcrosternum hilare(Hemiptera: Pentatomidae) in the United States

Abstract

Stink bugs (Hemiptera: Pentatomidae) are important economic pests of many agricultural crops, and have become one of the most difficult pest complexes to control in field crops, vegeta bles and fruit trees (McPherson & McPherson 2000). Stink bugs usually attack developing fruit ing structures, and direct damage to the fruit is caused by insertion of their stylets to feed on plant fluids. In soybeans (Glycine max (L.) Merr.), stink bug feeding can cause delayed maturity and reduce seed quality, yield and germination (Un derbill 1934; Chyen et al. 1992). The adoption of an early soybean production system has resulted in an increase in stink bug populations (Baur et al. 2000). The stink bug complex in the south contains the native spe cies Euschistus servus (Say) (brown stink bug), Nezara viridula (L.) (southern green stink bug) and Acrosternum hilare (Say) (green stink bug). (Taxonomists have proposed changing the name A. hilare to Chinavia hilaris (Say), but the En tomological Society of America has not approved this yet [David Rider, personal communication].) Historically, the southern green stink bug has had the greatest economic impact on southern USA soybean producers (Panizzi & Slansky 1985). Prior to 2000, Piezodorus guildinii (West wood) (redbanded stink bug) had never been an economic threat to soybean production in the U.S., although it has long been a serious pest in South America (Panizzi 1985). The redband ed stink bug has currently spread throughout Louisiana and is the dominant stink bug spe cies, comprising 59 to 72% of the total stink bugs found in soybean throughout the growing season (Temple et al. 2011a). Stink bug management can require multiple applications of broad-spectrum organophosphate or pyrethroid insecticides. The redbanded stink bug is very tolerant of many products available for stink bug control on soybean and, consequent ly, insecticide applications have significantly in creased (Temple et al. 2011b). Further, these in secticides applications negatively impact natural enemies, and may lead to population resurgences of other soybean pests (Panizzi & Slansky 1985). As a result, we are always watchful for possible biological control organisms that may reduce stink bug populations. During the summer of 2009, approximately 100 stink bugs were collected for bioassays from Louisiana soybean fields using 38-cm-diam sweep nets and returned to the laboratory. After about 24 h, mermithid nematodes were found to have emerged from field-collected adult, A. hilare and P. guildinii. The nematode from P. guildinii emerged on 6 Oct 2009, and had been collected from Ben Hur Research Station in Baton Rouge (30°22'14.3538N -91°9'52.236W) (Figs. 1A and IB). The nematode collected from A. hilare emerged on 30 Sep 2009 (Fig. 1C). It was collected at Macon Ridge Research Station in Winnsboro (32°8'1.6542 N -91°41'57.5484 W). An addi tional specimen was discovered in a 1992 insect collection emerging from a 4th instar nymph of A. hilare (Fig. ID) that had been preserved in 90% alcohol. This sample was collected 23 Sep 1992 from the Rice Research Station in Crowley (30°4'22.0416N -92°20'54.2112W). The rainfall for the 4 wk before emergence for all nematode infections was approximately 4.5-cm above aver age. The increased precipitation may have made the environment more conducive to the nema tode's survival.