G. L. Snodgrass

Toxicity of Insecticides in a Glass-Vial Bioassay to Adult Brown, Green, and Southern Green Stink Bugs (Heteroptera: Pentatomidae)

Adult brown, Euschistus servus (Say); green, Acrosternum hilare (Say); and southern green, Nezara viridula (L.), stink bugs were collected from soybean, Glycine max (L.) Merr., in fall 2001 and 2002 near Stoneville, MS, and Eudora, AR. A glass-vial bioassay was used to determine LC50 values for the three species of stink bugs for the pyrethroids bifenthrin, cypermethrin, cyfluthrin, lambda-cyhalothrin, and permethrin, and the organophosphates acephate, dicrotophos, malathion, and methyl parathion. Results confirmed findings of other researchers that the brown stink bug was less susceptible to pyrethroid and organophosphate insecticides than were green and southern green stink bugs. The susceptibility of all three stink bug species to the insecticides tested was very similar at both test locations. The study established baseline insecticide mortality data from two locations in the mid-South for three stink bug species that are pests of soybean and cotton, Gossypium spp. Data from the tests are valuable for future use in studies on resistance and in resistance monitoring programs.

Acephate Resistance in Populations of the Tarnished Plant Bug (Heteroptera: Miridae) From the Mississippi River Delta

ABSTRACT A monitoring program that used a glass-vial bioassay to detect acephate resistance in populations of the tarnished plant bug, Lygus lineolans (Palisot de Beauvois) (Heteroptera: Miridae), was carried out with weed-collected populations from 20 sites in the delta of Arkansas, Louisiana, and Mississippi. Additional results from field tests using recommended rates of formulated acephate in cotton showed that plant bug populations with resistance ratio (RR50) values >3.0 for acephate (from the glass-vial bioassay) would be difficult to control in the field. Over a 4-yr-period from 2001 through 2004, only one population tested with the glass-vial bioassay was found with an RR50 value >3.0 for acephate, but six populations having RR50 values >3.0 were found in the delta in 2005. In fall 2005, an additional 10 populations from the hill region (the cotton growing areas outside the delta) were tested and four of these populations had RR50 values >3.0. The number of populations with RR50 values >3.0 increased to five of 10 and 18 of 20 in the hills and delta, respectively, in fall 2006. Laboratory tests using resistant populations found that resistance to acephate was not sex-linked and the alleles controlling the resistance were semidominant in nature. Because of the large increase in resistant populations and the nature of the resistance found in this study, along with control problems experienced by growers in 2006, entomologists in the mid-South strongly recommended that alternation of insecticide classes in field treatments for plant bug control be used by growers in 2007. This control strategy probably helped control plant bugs in the hills of MS where plant bug pressure was low in 2007, and only one population was found in the fall with an RR50 value >3.0. Plant bug pressure was very high in many parts of the delta in 2007, and 15 of the 20 populations tested in the fall had RR50 values >3.0. In one field test in cotton, a population with multiple resistance was tested and not effectively controlled in treatments using recommended rates of carbamate, organophosphate, and pyrethroid insecticides. Alternation of insecticide classes may not work very well when populations are present that are resistant to three of the four main classes of cotton insecticides. New insecticides in different classes are badly needed for control of tarnished plant bugs in cotton in the mid-South.

Seasonal Changes in Pyrethroid Resistance in Tarnished Plant Bug (Heteroptera: Miridae) Populations During a Three-Year Period in the Delta Area of Arkansas, Louisiana, and Mississippi

Abstract Tarnished plant bugs, Lygus lineolaris (Palisot de Beauvois), were collected from weeds at 71 locations in the delta of Arkansas, Louisiana, and Mississippi and tested with a discriminating dose bioassay for pyrethroid resistance in the spring (April–May) and again at the same locations in the fall (September–October) in 1995–1997. Percentage of mortality in the discriminating dose bioassay declined significantly (pyrethroid-resistance increased) from spring to fall by an average 18.7, 21.3, and 21.7% in Arkansas, Louisiana, and Mississippi, respectively. Pyrethroid resistance declined significantly by 26.3% from the fall of 1995 to the spring of 1996 in Mississippi, but did not significantly decline in Arkansas (4.1%) and Louisiana (13.2%). Significant decreases in resistance occurred in all 3 states from the fall of 1996 to the spring of 1997 (17.1, 38.3, and 29.8% in Arkansas, Louisiana, and Mississippi, respectively). Plant bugs from 2 locations (Indianola, MS, and Wainwright, LA) had multiple insecticide resistance to a carbamate, 2 pyrethroid, and 4 organophosphorus insecticides. However, resistance to the organophosphate acephate in plant bugs from both locations was not significant. Possible causes for the significant increases and declines in resistance from season to season are discussed.

Cloning and expression profiling of odorant-binding proteins in the tarnished plant bug, Lygus lineolaris

In insects, the perception and discrimination of odorants requires the involvement of odorant‐binding proteins (OBPs). To gain a better molecular understanding of olfaction in the agronomic pest Lygus lineolaris (the tarnished plant bug), we used a transcriptomics‐based approach to identify potential OBPs. In total, 33 putative OBP transcripts, including the previously reported Lygus antennal protein (LAP), were identified based on the characteristic OBP Cys signature and/or sequence similarity with annotated orthologous sequences. The L. lineolaris OBP (LylinOBP) repertoire consists of 20 ‘classic’ OBPs, defined by the spacing of six conserved Cys residues, and 12 ‘Plus‐C’ OBPs, defined by the spacing of eight conserved Cys and one conserved Pro residue. Alternative splicing of OBP genes appears to contribute significantly to the multiplicity of LylinOBP sequences. Microarray‐based analysis of chemosensory tissues (antennae, legs and proboscis) revealed enrichment of 21 LylinOBP transcripts in antennae, 12 in legs, and 15 in proboscis, suggesting potential roles in olfaction and gustation respectively. PCR‐based determination of transcript abundance for a subset of the LylinOBP genes across multiple adult tissues yielded results consistent with the hybridization data.

Plant Host Effect on the Development of Heliothis virescens F. (Lepidoptera: Noctuidae)

Abstract Heliothis virescens F. is an important polyphagous pest that can develop on >100 plant species, including 20 economic crops. Populations of this insect are believed to be locally maintained on a few crops and weed hosts in Washington County, MS. To find the intrinsic value of these plants for the development of H. virescens populations, we fed different laboratory and wild colonies with fresh and lyophilized plant tissue under a constant temperature. Development time of this insect under laboratory conditions varied up to 10 d between plant hosts and was dependent on the type of plant tissue provided: fresh or lyophilized. Life table parameters such as net reproductive rate, finite rate of increase, and generation time indicated that Trifolium repens, a wild host growing around agricultural fields year round, could be one of the most suitable local plant hosts for the development of H. virescens. Two species of Geranium, previously reported as the source of the first H. virescens generation in the region, had lower intrinsic value as a food source than did T. repens. Gossyipium hirsutum, perhaps the most important crop source of H. virescens in the region, produced low net reproductive rate and finite rate of increase parameters. Sampling conducted in agricultural fields during 2006 and 2007 found no larvae on the above mentioned wild hosts as it was previously reported. Results indicated that H. virescens populations in this region were not supported by the wild plant species growing around agricultural fields during the time when the survey took place.

Influence of Soybean Planting Date and Maturity Group on Stink Bug (Heteroptera: Pentatomidae) Populations

Abstract Field experiments were conducted in Stoneville, MS, to determine the impact of soybean planting date and maturity group on stink bug (Heteroptera: Pentatomidae) populations. Maturity group IV and V soybeans were planted on three planting dates in 2003 and 2004. Planting dates were late March-early April, late April-early May, and late May-early June. Plots were sampled weekly with a standard 38.1-cm-diameter sweep net. Planting date and maturity group each had a significant effect on stink bug populations. In general, the earliest planting date had the lowest densities of stink bugs, whereas the latest planting date had the highest densities of stink bugs. Over the 2-yr period, cumulative numbers of stink bugs (SE) ranged from 17.9 (6.25) per 25 sweeps for the first planting to 190.9 (20.03) per 25 sweeps for the third planting date when averaged across maturity groups. Additionally, stink bug populations were generally lower on maturity group IV soybeans than on maturity group V soybeans. Cumulative numbers of stink bugs on maturity group IV soybeans averaged 52.4 (26.23) and 25.2 (6.93) in 2003 and 2004, respectively. On maturity group V soybeans, cumulative numbers of stink bugs averaged 96.9 (28.05) and 85.7 (40.84) in 2003 and 2004, respectively. These data provide valuable information about the population dynamics of stink bugs and indicate that early plantings of maturity group IV soybeans in the mid-South will escape heavy stink bug densities.

Role of Reproductive Diapause in the Adaption of the Tarnished Plant Bug (Heteroptera: Miridae) to Its Winter Habitat in the Mississippi River Delta

Abstract Reproductive diapause in the tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), was studied by dissection of field collected adults or adults reared from field collected nymphs in 1999–2001 in Washington County near Stoneville, MS. The critical photoperiod for diapause induction was 12.5:11.5 (L:D) h, or ≈12 September. This photoperiod was also near the day-length at which new generation adults produced in late winter and early spring became reproductive. Overwintering adults collected from winter host plants in December 1999 and 2001 began breaking diapause in the second and third weeks of December at a day-length near 10:14 (L:D) h. Most of the overwintering females collected on winter host plants had mature eggs by the end of December in both winters, and new generation adults were produced on winter hosts by the second or third week in March. Overwintering adults also were collected in January 2002 from plant debris not associated with any winter host plant. Most of the females overwintering in plant debris had mature eggs at the end of January, approximately 1 month later than overwintering females collected from winter hosts. This indicated than the adults from plant debris were in a different state of diapause, because they did not overwinter on a food source and matured reproductively at a later date. The winters of 1998–1999 and 1999–2000 were mild, whereas in the winter of 2000–2001, winter host plants were killed or stunted by cold weather. Diapause in plant debris in the winter of 2000–2001 was probably favored, because these adults would be more likely to survive until suitable host plants were available.

Suppression of Tarnished Plant Bugs (Heteroptera: Miridae) in Cotton by Control of Early Season Wild Host Plants with Herbicides

Abstract Broadleaf weeds found in marginal areas by fields, roads, and ditches were controlled with herbicides in 23-km2 areas of the Mississippi Delta in March or April of 1999, 2000, and 2001. There were two treated and two untreated 23-km2 areas in each of the 3 test yr. The herbicides used were Trimec® or Strike 3™, and both contain mecoprop, 2, 4-D, and dicamba. Broadleaf weeds can serve as early season food and reproductive hosts for tarnished plant bugs, and population buildups can occur on these weeds before movement of plant bugs into cotton. Cotton fields in the treated sites and in untreated 23-km2 sites were sampled for tarnished plant bugs weekly during June and July of all 3 yr. Overall mean numbers of tarnished plant bugs were significantly lower in cotton in the treated areas. The average reduction in overall mean numbers of plant bugs was 50% for the 3-yr period. Grower costs for insecticides used to control plant bugs were lower in cotton in the treated test sites in all 3 yr. The average net savings in plant bug control costs was estimated at

Identification of the western tarnished plant bug (Lygus hesperus) olfactory co-receptor Orco: expression profile and confirmation of atypical membrane topology.

35,477/yr for growers in the treated areas over the 3 yr of the study. Elimination of broadleaf weeds was found to be an effective method for reducing numbers of plant bugs in cotton. However, it did not reduce numbers of tarnished plant bugs in any year to a level in cotton where additional control with insecticides was not needed.

Tarnished Plant Bug (Heteroptera: Miridae) Populations near Fields After Early Season Herbicide Treatment

Lygus hesperus (western tarnished plant bug) is an agronomically important pest species of numerous cropping systems. Similar to other insects, a critical component underlying behaviors is the perception and discrimination of olfactory cues. Consequently, the molecular basis of olfaction in this species is of interest. To begin to address this issue, we utilized homology-based PCR as a commonly accepted abbreviation but if necessary it is polymerase chain reaction methods to identify the L. hesperus olfactory receptor co-receptor (Orco) ortholog, a receptor that has been shown to be essential for olfaction. The L. hesperus Orco (LhOrco) shares significant sequence homology with known Orco proteins in other insects. Parallel experiments using the sympatric sister species, Lygus lineolaris (tarnished plant bug), revealed that the Lygus Orco gene was completely conserved. Surprisingly, a majority of the membrane topology prediction algorithms used in the study predicted LhOrco to have both the N and C terminus intracellular. In vitro immunofluorescent microscopy experiments designed to probe the membrane topology of transiently expressed LhOrco, however, refuted those predictions and confirmed that the protein adopts the inverted topology (intracellular N terminus and an extracellular C terminus) characteristic of Orco proteins. RT-PCR analyses indicated that LhOrco transcripts are predominantly expressed in adult antennae and to a lesser degree in traditionally nonolfactory chemosensory tissues of the proboscis and legs. Expression is not developmentally regulated because transcripts were detected in all nymphal stages as well as eggs. Taken together, the results suggest that LhOrco likely plays a critical role in mediating L. hesperus odorant perception and discrimination.