Effectiveness of Microbial and Chemical Insecticides for Supplemental Control of Bollworm on Bt and Non-Bt Cottons.

Laboratory and field experiments were conducted to determine the effectiveness of microbial and chemical insecticides for supplemental control of bollworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), on non-Bt (DP1441RF) and Bt (DP1321B2RF) cottons. Neonate and 3rd instar larvae survival was evaluated on leaf tissue treated with microbial and chemical insecticides including a commercial formulation of Bacillus thuringiensis (Dipel), a Heliothis (Helicoverpa) nuclear polyhedrosis virus (NPV; Gemstar), λ-cyhalothrin (Karate Z), and chlorantraniliprole (Prevathon). Residual activity of insecticides was measured in a small plot field experiment. The performance of microbial insecticides, with the exception of a mid-rate of Dipel with neonate larvae, was comparable with that of chemical treatments on non-Bt cotton leaves with regard to 1st and 3rd instar bollworm mortality at 10 d and pupal eclosion at 20-d post treatment. Production-level field evaluations of supplemental bollworm control in non-Bt and Bt cottons with NPV, λ-cyhalothrin, and chlorantraniliprole were also conducted. During both years of the field study, all chemical and microbial treatments were successful in suppressing bollworm larval densities in non-Bt cotton below economic threshold levels. Overall, net returns above bollworm control, regardless of treatment, were negatively correlated with larval abundance and plant damage. In addition, there was no economic benefit for supplemental control of bollworms in Bt cotton at the larval densities observed during this study. These data provide benchmark comparisons for insect resistance management with microbial and chemical insecticides in Bt and non-Bt cottons and strategic optimization of the need to spray non-Bt and Bt cotton in IRM programs.

Demographic Parameters of Nezara viridula (Heteroptera: Pentatomidae) Reared on Two Diets Developed for Lygus spp.

Two artificial diets developed for rearing Lygus spp., a fresh yolk chicken egg based-diet (FYD) and a dry yolk chicken egg based-diet (DYD), were evaluated as an alternative food source for rearing the southern green stink bug, Nezara viridula (L.) (Heteroptera: Pentatomidae). Survival to adult was 97.3 and 74.67%, respectively, on the fresh and dry yolk diets. Insects fed FYD had 100% survival of nymphs from first through fourth instars. Adult development was significantly shorter on FYD (30.37 ± SE 0.30 d) as compared with DYD (32.77 ± SE 0.16 d). Increased male and female longevity, higher fecundity, and larger egg mass sizes were also observed with N. viridula-fed FYD. However, fertility and hatchability was higher on DYD. A complete cohort life table was constructed to describe the development of N. viridula on both diets.

Effect of food and temperature on emergence from diapause in the tarnished plant bug (Hemiptera: Miridae).

Tarnished plant bugs, Lygus lineolaris (Palisot de Beauvois), overwinter as diapausing adults in North America. Overwintering adults were collected near Stoneville, MS from blooming henbit, Lamium amplexicaule L., and from plant debris during December and January and dissected to determine their reproductive status. Averaged over four winters, male and female tarnished plant bugs collected from henbit terminated diapause at a significantly higher rate than males and females from plant debris during each week of December and the first week of January. Both sexes in each habitat were nearly all reproductive by the end of January. Adults overwintering in plant debris terminated diapause during January in the absence of a food stimulus in all 5 yr studied. This emergence was thought to be controlled by an internal clock. Laboratory and field studies showed that emergence from diapause could be influenced by food, sex, and temperature. Adults overwintering on a suitable food source, blooming henbit, terminated diapause during December in the 4 yr studied, and males terminated diapause more rapidly than females. Food quality was important in emergence from diapause, and females on blooming henbit terminated diapause at a significantly higher rate than females on nonblooming mustard, Brassica juncea (L.) Cosson. Laboratory tests showed that diapausing adults reared in the laboratory and held at a diapause-maintaining photoperiod of 10:14 (L:D) h could be terminated from diapause by using food and temperature stimuli. The lower thermal threshold for development to reproductive adults was found to be near 10°C. The ability of diapausing adults to respond to food and temperature stimuli in December can enable tarnished plant bugs to take advantage of warm winters and winter hosts to produce a new generation earlier.

Susceptibility of Helicoverpa zea and Heliothis virescens (Lepidoptera: Noctuidae) to Vip3A insecticidal protein expressed in VipCot™ cotton.

Susceptibility of laboratory and field colonies of Helicoverpa zea (Boddie) and Heliothis virescens F. to Vip3A insecticidal protein was studied in diet incorporation and diet overlay assays from 2004 to 2008. Responses of field populations were compared to paired responses of University of Arkansas laboratory susceptible H. zea (LabZA) and H. virescens (LabVR) colonies. After 7d of exposure, observations were made on number of dead larvae (M) and the number of larvae alive but remaining as first instars (L1). Regression estimates using M (LC(50)) and M plus L1 (MIC(50)) data were developed for laboratory and field populations. Susceptibility of laboratory and field populations exposed to Vip3A varied among different batches of protein used over the study period. Within the same batch of Vip3A protein, susceptibilities of laboratory colonies of both species (LabZA and LabVR) were similar. Field colonies were significantly more susceptible to Vip3A than the respective reference colonies of both species. Within field populations, susceptibility to Vip3A varied up to 75-fold in H. zea and 132-fold in H. virescens in LC(50) estimates. Variabilities in MIC(50)s were up to 59- and 11-fold for H. zea and H. virescens, respectively.

Response estimates for assessing heliothine susceptibility to Bt toxins.

Field and laboratory colonies of Helicoverpa zea (Boddie) and Heliothis virescens (F.) were exposed to CrylAc and Cry2Ab2 toxins to compare different mortality and mortality + stunting responses. Lethal concentrations for mortality (LC(50S)), molt inhibitory concentrations for mortality + surviving L1 larvae (MIC(50S)), and inhibitory concentrations for mortality + surviving L1 and L2 larvae (IC(50S) were established to describe the different responses across a range of test concentrations. MIC(50S) and IC(60(50S) at 7 d significantly correlated to LCsos at 7 d, but MIC(50S) were more closely correlated with LC(50S) than IC(50S). Experiments conducted to determine the fate of survivors (larval stage L1, L2, or L3 larvae) after 7 d of exposure of Bt toxin and transfer to untreated or Bt-treated diet revealed that significant numbers of stunted larvae recovered and survived to pupation. Percentage of survival was significantly higher for larvae fed untreated diet after 7 d on Bt-treated diet, but a few survivors also were found when larvae were fed only Bt diet. Survival to pupation of larvae classified as L1 at 7 d was significantly lower than those for L2 or L3 larvae at 7 d, indicating that many stunted larvae suffer chronic effects of the initial exposure to Bt and fail to reach the next life stage. Pupation of larvae classified as L1 at 7d was reduced and delayed in comparison with those for L2 and L3 larvae at 7d. Collectively, these data suggest that MIC50 estimates at 7 d more accurately project total larval mortality from Bt exposure than do LC50 or IC50 at 7 d.

Early-season soybean as a trap crop for stink bugs (Heteroptera: Pentatomidae) in Arkansas' changing system of soybean production.

Early-season soybean, Glycine max L. Merrill, was evaluated in Arkansas soybean fields as a trap crop for a complex of stink bug species that included Nezara viridula L., Acrosternum hilare (Say), and Euschistus servus (Say). Early-season soybean production systems (ESPSs) are composed of indeterminate soybean cultivars planted in April. In the first year of a 2-yr study, field-scale trap crops ( approximately 0.5-1.0 ha) of maturity group (MG) III and IV soybean were planted adjacent to production fields of MG V soybean. Stink bugs were attracted first to the ESPS trap crops and were twice treated with insecticide, yet damaging populations developed later in the MG V soybean adjacent to the trap crops. General sampling and observations of low stink bug densities in commercial fields of soybean and corn across the study area suggested that stink bugs were widely distributed across the agricultural landscape. These observations and the subsequent discovery of additional ESPS fields outside the study area suggested that developing populations in the adjacent MG V soybean probably did not originate from the trap crops. However the source of the populations colonizing MG V soybean could not be determined, and we concluded that the scale of future experiments should be increased to better control stink bugs dispersing from other ESPSs outside the study area. In the second year of the study, the experiment was expanded in size to a farm- or community-scale project where entire fields of ESPSs (8-32 ha) were used as trap crops. Insecticide was applied to the trap-crop fields and other fields of ESPSs within a 0.8-km radius of targeted response fields, yet again there was no apparent effect on subsequent populations of stink bugs in the MG V response fields. With the recent expansion of ESPSs in Arkansas, it may be difficult to use ESPSs as a trap crop to lower stink bug populations across large enough areas to suppress populations in late-season soybean. Also, multiple soybean cultivars are generally planted across a 2- or 3-mo period in Arkansas, which results in staggered soybean development across the landscape and extends the time period that soybean is attractive to colonizing stink bugs. Trap crops of ESPSs are only attractive for oviposition for up to 4-5 wk and cannot protect full-season soybean production systems (FSSPSs) for such an extended time period. This shift in production systems may limit the use of ESPS trap crops for management of stink bugs unless highly coordinated efforts are made to synchronize soybean maturity and control stink bugs in ESPSs across large geographic areas.

Seasonal abundance, species composition, and population dynamics of stink bugs in production fields of early and late soybean in South Arkansas.

From 2003 through 2007, densities of stink bugs were monitored weekly in 297 commercial production fields of early and late soybean, Glycine max L. Merrill, in southeast and southwest Arkansas. The goal of this research was to better understand seasonal abundance, species composition, and population dynamics of pentatomids as a benchmark reference for future management systems. Thirty-five percent of all the 25-sweep samples taken in soybean contained at least one stink bug specimen. The average density (mean +/- SEM) of stink bugs across all soybean samples was 1.84 +/- 0.06 per 25 sweeps. Overall, Nezara viridula L. was the most abundant species, although Euschistus serous (Say) was frequently found in soybean samples (18% of all samples). Peak densities of stink bugs in soybean were observed during the full-pod (R7) developmental stage. Approximately 25% of all soybean fields sampled had threshold densities (nine or more per 25 sweeps) at some time during the year, although 82 and 78% of fields in 2006 and 2007, respectively, reached threshold. At low densities (one to three stink bugs per 25 sweeps), E. serous comprised 50% of total stink bugs, but at high densities (> 71 stink bugs per 25 sweeps), N. viridula comprised 81% of total stink bugs. Piezodorus guildinii (Westwood) was observed as a pest of Arkansas soybean in 2005, and reproduction in soybean was documented in 2006 and 2007. Stink bugs seem to be a serious and increasingly important pest of soybean in southern Arkansas. Crop phenological development is a key factor in predicting colonization and population growth of stink bugs on Arkansas soybean, regardless of geographic region or type of soybean production system.

Susceptibility of bollworm and tobacco budworm (Lepidoptera: Noctuidae) to Cry2Ab2 insecticidal protein.

Susceptibilities of 82 bollworm, Helicoverpa zea (Boddie), and 44 tobacco budworm, Heliothis virescens (F.) (Lepidoptera: Noctuidae), populations to Cry2Ab2 protein were measured in diet incorporated assays at the University of Arkansas from 2002 to 2005. Resulting data were used to calculate overall (pooled data) estimates of species susceptibility for future benchmarks of resistance. Variabilities among populations also were studied by comparing regressions for individual populations and calculating mean susceptibilities for different subgroups of the colonies studied. Individual lethal concentration (LC50) estimates for nine laboratory, seven laboratory-cross, and 28 field populations of H. virescens varied up to 48-fold when adjusted for the response of the most susceptible laboratory colony studied. Mean susceptibilities of all laboratory, laboratory-cross, or field colonies varied only two-fold. When grouped by host plants, populations collected on tobacco, Nicotiana tabacum (L.), seemed to be less susceptible than those collected on other host plants. Individual LC50 values for 82 laboratory, laboratory-cross and field populations of H. zea varied up to 37-fold. Mean LC50 values of all laboratory, laboratory-cross, or field populations varied only three-fold. Susceptibilities of populations from Bollgard cotton were up to four-fold less than those from Bacillus thuringiensis corn, Zea mays L. Field populations collected during late season were generally less susceptible than those collected early in the season. Across the two species, H. zea was less sensitive to Cry2Ab2 than H. virescens. Both species seem to be less sensitive to Cry2Ab2 than to CrylAc.

Susceptibilities of Helicoverpa zea and Heliothis virescens (Lepidoptera: Noctuidae) populations to Cry1Ac insecticidal protein.

Susceptibilities of bollworm, Helicoverpa zea (Boddie) and tobacco budworm, Heliothis virescens (F.) to Cry1Ac were measured via a diet-incorporated assay with MPV II at the University of Arkansas during 2002-2004. Lethal concentration-mortality (LC50) estimates of five laboratory, seven laboratory-cross, and 10 field populations of H. virescens varied 12-fold. Pooled susceptibilities of H. virescens across all laboratory and field populations varied five-fold. The LC50 estimates for H. virescens were higher than those reported by previous research before the introduction of transgenic crops. However, the ratio of susceptibility of laboratory and field populations was similar, suggesting no change in overall species susceptibility. Individual LC50 estimates of five laboratory, nine laboratory-cross, and 57 field populations of H. zea varied over 130-fold. Pooled susceptibilities across laboratory and field populations varied widely. Among the field populations, colonies from non-Bacillus thuringiensis (Bt) crops were generally more susceptible than those from Bt crops. Across the Bt crops expressing Cry protein, colonies from Bollgard (Monsanto Company) cotton had lower susceptibility to CrylAc than those from Bt corn and those from non-Bt crops.

Interplant movement of Heliothis virescens (Lepidoptera: Noctuidae) larvae in pure and mixed plantings of cotton with and without expression of the Cry1Ac delta-endotoxin protein of Bacillus thuringiensis Berliner.

Laboratory and field studies were conducted during 1993 and 1994 to quantify interplant movement of Heliothis virescens (F.) larvae in pure and mixed plantings of cotton, Gossypium hirsutum L., with ('Event 531') and without ('Coker 312') the expression of Cry1Ac delta-endotoxin protein of Bacillus thuringiensis Berliner. Field studies were conducted with neonate, 4-, and 7-d-old larvae placed on 3-plant experimental units and observed at 24, 48, 72, and 96 h after inoculation of larvae. Combining larval movement across observations of neonates, 4-, and 7-d-old larvae, an estimated 52% of the larvae on pure plantings of Coker 312 had moved at least 1 plant by the cumulative time required to reach the age of 10 d. More larvae placed on Event 531 cotton moved to an adjacent plant (13% of the neonates had moved at least 1 plant within 24 h) than those placed on Coker 312 (0% of the neonates had moved at least 1 plant within 24 h). When larvae were placed on Event 531 plants, an estimated 82% of the larvae had moved to an adjacent plant by cumulative age of 10 d. Collectively, these data indicate that movement of larvae from plant to plant increases with larval age and occurs more rapidly for larvae placed on Event 531 cotton than on Coker 312. Previous studies have suggested that resistance to B. thuringiensis could develop more rapidly in insects exposed to seed mixtures of plants with and without endotoxin if larvae move between plants and if an external refuge exists. These data provide evidence of larval movement between plants in seed mixtures.

Characterization of naturally occurring atrazine-resistant isolates of the purple non-sulfur bacteria.

Six isolates of the purple non-sulfur bacteria, which upon primary isolation were naturally resistant to the herbicide atrazine, were characterized with respect to their taxonomic identity and the mechanism of their resistance. On the basis of electron microscopy, photopigment analysis, and other criteria, they were identified as strains of Rhodopseudomonas acidophila, Rhodopseudomonas palustris, or Rhodocyclus gelatinosus. These isolates exhibited degrees of atrazine resistance which ranged from 1.5 to about 4 times greater than that of cognate reference strains (American Type Culture Collection) tested. Furthermore, all of the reference strains tested were more intrinsically resistant to atrazine than was Rhodobacter sphaeroides. No unique plasmids which might encode for herbicide degradation or inactivation were found in these isolates. Resistance to the herbicide in these isolates was not the result of diminished binding of the herbicide to the L subunit of the bacterial reaction center. Differences in herbicide resistance among the various species of this group may be the result of compositional and chemical differences in the individual reaction centers. However, the increase in atrazine resistance for the isolates characterized in this study probably occurs by undefined mechanisms and not necessarily by changes in the binding of the herbicide to the L subunit of the photosynthetic reaction center.

Kluyvera species soft tissue infection: case report and review.

A soft tissue infection caused by Kluyvera species in a previously healthy woman is described. Successful treatment required incision and drainage of the wound in addition to administration of antibiotics. Kluyvera species are indole positive, Voges-Proskauer negative members of the family Enterobacteriaceae. Previous reports of infection due to Kluyvera species suggest that the organism is never more than an opportunistic pathogen; however, we report the first case of infection in a previously healthy host.