Host Preference of Megacopta cribraria (Hemiptera: Plataspidae) on Selected Edible Beans and Soybean.

Megacopta cribraria (F.) (Hemiptera: Plataspidae) is an Old World pest of legumes in Asia. Since its 2009 discovery in Georgia, it has become an economic pest of soybeans in the southeastern United States. The objective of this study was to determine the host preference of M. cribraria on edible legumes that might incur economic damage from injury of this pest. From 2012 to 2013 choice, no-choice, and field trials were conducted to evaluate the host suitability of several beans of commercial interest including pinto bean, lima bean, winter pea, and black-eyed pea. Choice and no-choice studies were conducted under greenhouse conditions. Plants in greenhouse trials were infested with adults and egg masses collected from kudzu and soybean and monitored for ∼2 wk. Field trials were allowed to be infested by naturally occurring M. cribraria populations. Sweep and whole plant counts of adults, egg masses, and nymphs were used to quantify field infestations. The legume crops found to be suitable developmental hosts are soybean, edamame, and pigeon pea. Low levels of development were seen on fava bean and none on the remaining entries.

Efficacy of Silk Channel Injections with Insecticides for Management of Lepidoptera Pests of Sweet Corn.

The primary Lepidoptera pests of sweet corn (Zea mays L. convar. saccharata) in Georgia are the corn earworm, Helicoverpa zea (Boddie), and the fall armyworm, Spodoptera frugiperda (J. E. Smith). Management of these pests typically requires multiple insecticide applications from first silking until harvest, with commercial growers frequently spraying daily. This level of insecticide use presents problems for small growers, particularly for "pick-your-own" operations. Injection of oil into the corn ear silk channel 5-8 days after silking initiation has been used to suppress damage by these insects. Initial work with this technique in Georgia provided poor results. Subsequently, a series of experiments was conducted to evaluate the efficacy of silk channel injections as an application methodology for insecticides. A single application of synthetic insecticide, at greatly reduced per acre rates compared with common foliar applications, provided excellent control of Lepidoptera insects attacking the ear tip and suppressed damage by sap beetles (Nitidulidae). While this methodology is labor-intensive, it requires a single application of insecticide at reduced rates applied ∼2 wk prior to harvest, compared with potential daily applications at full rates up to the day of harvest with foliar insecticide applications. This methodology is not likely to eliminate the need for foliar applications because of other insect pests which do not enter through the silk channel or are not affected by the specific selective insecticide used in the silk channel injection, but would greatly reduce the number of applications required. This methodology may prove particularly useful for small acreage growers.

Multi-state trials of Bt sweet corn varieties for control of the corn earworm (Lepidoptera: Noctuidae).

Field tests in 2010-2011 were performed in New York, Minnesota, Maryland, Ohio, and Georgia to compare Bt sweet corn lines expressing Cry1A.105 + Cry2Ab2 and Cry1Ab with their non-Bt isolines, with and without the use of foliar insecticides. The primary insect pest in all locations during the trial years was Heliocoverpa zea (Boddie), which is becoming the most serious insect pest of sweet corn in the United States. At harvest, the ears were measured for marketability according to fresh market and processing standards. For fresh market and processing, least squares regression showed significant effects of protein expression, state, and insecticide frequency. There was a significant effect of year for fresh market but not for processing. The model also showed significant effects of H. zea per ear by protein expression. Sweet corn containing two genes (Cry1A.105 + Cry2Ab2) and a single gene (Cry1Ab) provided high marketability, and both Bt varieties significantly outperformed the traditional non-Bt isolines in nearly all cases regardless of insecticide application frequency. For pest suppression of H. zea, plants expressing Bt proteins consistently performed better than non-Bt isoline plants, even those sprayed at conventional insecticide frequencies. Where comparisons in the same state were made between Cry1A.105 + Cry2Ab2 and Cry1Ab plants for fresh market, the product expressing Cry1A.105 + Cry2Ab2 provided better protection and resulted in less variability in control. Overall, these results indicate Cry1A.105 + Cry2Ab2 and Cry1Ab plants are suitable for fresh market and processing corn production across a diversity of growing regions and years. Our results demonstrate that Bt sweet corn has the potential to significantly reduce the use of conventional insecticides against lepidopteran pests and, in turn, reduce occupational and environmental risks that arise from intensive insecticide use.

First Report of Iris yellow spot virus in Spiny Sowthistle (Sonchus asper) in the United States.

Iris yellow spot virus (IYSV) is a member of the genus Tospovirus in the family Bunyaviridae. Its known host range is very limited, and the currently known hosts include onion, leek, lisianthus, and alstroemeria (2). The virus is vectored by onion thrips (Thrips tabaci). Onion (Allium cepa) is grown as a winter crop in Georgia from September to April and is the only known host commercially grown in the region. However, the virus has been found across the onion-growing region in the state every year since its first occurrence during 2003 (3). Consequently, the virus must oversummer in other host(s) or its insect vector. Accordingly, samples of weeds were collected in the vicinity of onion fields and cull piles in the Vidalia region and tested for the presence of IYSV by a double-antibody sandwich (DAS)-ELISA (Agdia, Inc., Elkhart, IN). One of three nonsymptomatic spiny sowthistle samples tested positive by ELISA for IYSV. Total RNA was extracted from the leaf using the RNeasy Plant Mini Kit (Qiagen, Valencia, CA) following the manufacturer's protocol. Two microliters were used for reverse transcription (RT)-PCR with the forward primer (5'-TCAGAAATCGAGAAACTT-3') and reverse primer (5'-TAATTATATCTATCTTTCTTGG-3') for the IYSV nucleocapsid gene (1). A band of the expected size (approximately 800 bp) was obtained and sequenced. The sequence from the sowthistle (GenBank Accession No. EU078327) matched IYSV sequences from Georgia and Peru in a BLAST search in GenBank (closest matches with Accession Nos. DQ838584, DQ838592, DQ838593, and DQ658242). This is to our knowledge, the first confirmed report of IYSV infecting spiny sowthistle. The distribution of IYSV in sowthistle and its role as an oversummering host for IYSV is currently an on-going study. References: (1) L. du Toit et al. Plant Dis. 88:222, 2004. (2) D. H. Gent et al. Plant Dis. 90:1468, 2006. (3) S. W. Mullis et al. Plant Dis. 88:1285, 2004.

First Report of Vidalia Onion (Allium cepa) Naturally Infected with Tomato spotted wilt virus and Iris yellow spot virus (Family Bunyaviridae, Genus Tospovirus) in Georgia.

Vidalia onion is an important crop in Georgia's agriculture with worldwide recognition as a specialty vegetable. Vidalia onions are shortday, Granex-type sweet onions grown within a specific area of southeastern Georgia. Tomato spotted wilt virus (TSWV) has been endemic to Georgia crops for the past decade, but has gone undetected in Vidalia onions. Tobacco thrips (Frankliniella fusca) and Western flower thrips (Frankliniella occidentalis) are the primary vectors for TSWV in this region, and a number of plant species serve as reproductive reservoirs for the vector or virus. Iris yellow spot virus (IYSV), an emerging tospovirus that is potentially a devastating pathogen of onion, has been reported in many locations in the western United States (2,4). Thrips tabaci is the known vector for IYSV, but it is unknown if noncrop plants play a role in its epidemiology in Georgia. During October 2003, a small (n = 12) sampling of onions with chlorosis and dieback of unknown etiology from the Vidalia region was screened for a variety of viruses, and TSWV and IYSV infections were serologically detected. Since that time, leaf and bulb tissues from 4,424 onion samples were screened for TSWV and IYSV using double antibody sandwich-enzyme linked immunosorbent assay (DAS-ELISA) with commercial kits (Agdia Inc., Elkhart, IN). Samples were collected from 53 locations in the Vidalia region during the growing season between November 2003 and March 2004. Plants exhibiting stress, such as tip dieback, necrotic lesions, chlorosis or environmental damage were selected. Of these, 306 were positive for TSWV and 396 were positive for IYSV using positive threshold absorbance of three times the average plus two standard deviations of healthy negative onion controls. Positive serological findings of the onion tissues were verified by immunocapture-reverse transcription-polymerase chain reaction (IC-RT-PCR) for TSWV (3) and RT-PCR for IYSV (1). In both instances, a region of the viral nucleocapsid (N) gene was amplified. The PCR products were analyzed with gel electrophoresis with an ethidium bromide stain in 0.8% agarose. Eighty-six percent (n = 263) of the TSWV ELISA-positive samples exhibited the expected 774-bp product and 55 percent (n = 217) of the IYSV ELISA-positive samples exhibited the expected 962-bp product. The reduced success of the IYSV verification could be attributed to the age and deteriorated condition of the samples at the time of amplification. Thrips tabaci were obtained from onion seedbeds and cull piles within the early sampling (n = 84) and screened for TSWV by the use of an indirect-ELISA to the nonstructural (NSs) protein of TSWV. Of the thrips sampled, 25 were positive in ELISA. While the incidence of IYSV and TSWV in the Vidalia onion crop has been documented, more research is needed to illuminate their potential danger to Vidalia onions. References: (1) I. Cortês et al. Phytopathology 88:1276, 1998. (2) L. J. du Toit et al. Plant Dis. 88:222, 2004. (3) R. K. Jain et al. Plant Dis. 82:900, 1998. (4) J. W. Moyer et al. (Abstr.) Phytopathology 93(suppl.):S115, 2003.

Trace chemicals: the essence of sexual communication systems in heliothis species.

Analysis of heptane-soluble compounds from ovipositors of Heliothis zea and Heliothis virescens shows that both species produce relatively large amounts of (Z)-11-hexadecenal, with traces of (Z)-9-hexadecenal, (Z)-7-hexadecenal, and hexadecanal. Heliothis virescens females differ from Heliothis zea in that they also produce trace amounts of tetradecanal, (Z)-9-tetradecenal, and (Z)-11-hexadecen-1-ol. In both species, trace compounds are essential to pheromonal activity and specificity of chemical signals.