G. David Buntin

Cry1F Resistance in Fall Armyworm Spodoptera frugiperda: Single Gene versus Pyramided Bt Maize

Evolution of insect resistance to transgenic crops containing Bacillus thuringiensis (Bt) genes is a serious threat to the sustainability of this technology. However, field resistance related to the reduced efficacy of Bt maize has not been documented in any lepidopteran pest in the mainland U.S. after 18 years of intensive Bt maize planting. Here we report compelling evidence of field resistance in the fall armyworm, Spodoptera frugiperda (J.E. Smith), to Cry1F maize (TC 3507) in the southeastern region of the U.S. An F2 screen showed a surprisingly high (0.293) Cry1F resistance allele frequency in a population collected in 2011 from non-Bt maize in south Florida. Field populations from non-Bt maize in 2012–2013 exhibited 18.8-fold to >85.4-fold resistance to purified Cry1F protein and those collected from unexpectedly damaged Bt maize plants at several locations in Florida and North Carolina had >85.4-fold resistance. In addition, reduced efficacy and control failure of Cry1F maize against natural populations of S. frugiperda were documented in field trials using Cry1F-based and pyramided Bt maize products in south Florida. The Cry1F-resistant S. frugiperda also showed a low level of cross-resistance to Cry1A.105 and related maize products, but not to Cry2Ab2 or Vip3A. The occurrence of Cry1F resistance in the U.S. mainland populations of S. frugiperda likely represents migration of insects from Puerto Rico, indicating the great challenges faced in achieving effective resistance management for long-distance migratory pests like S. frugiperda.

Effect of Bacillus thuringiensis Transgenic Corn for Lepidopteran Control on Nontarget Arthropods

Abstract Field populations of nontarget arthropods in transgenic corn with the MON 810 event expressing the Cry1Ab endotoxin from Bacillus thuringiensis variety kurstaki (Bt) were compared with those in conventional, near isogenic corn. The study was conducted at two locations in Georgia in 2001 and 2002 using visual counts, pitfall traps, and corn ear insect evaluations. Results were analyzed by trial using a repeated-measure analysis of variance (ANOVA) and a combined ANOVA of all trials. The only insect whose numbers were strongly affected by the Bt corn was the corn earworm, Helicoverpa zea (Boddie), a target insect. When averaged over all trials, larvae and adults of sap beetles, Carpophilus spp. (mostly C. lugubris Murray), and larvae of the otitid fly Euxesta stigmatis Loew were less abundant on Bt than non-Bt corn ears. Kernel damage caused by H. zea was less in Bt corn, which presumably made Bt corn ears less attractive to these insects. There were no consistent significant differences in nontarget phytophagous and predaceous arthropods in the visual counts and pitfall traps between Bt and non-Bt corn. One exception was Nabis spp., which was less abundant in Bt than non-Bt corn in the combined analysis. Flea beetles, mostly corn flea beetle, Chaetocnema pulicaria Melsheimer, were more abundant on Bt than non-Bt corn in the combined analysis but presumably were not adversely affected by the Bt corn. With the exception of nabids, these results indicate that transgenic Bt field corn containing the MON 810 event did not have an adverse effect on populations of nontarget phytophagous or predaceous arthropods in the Georgia corn system.

EVALUATION OF YIELDGARD TRANSGENIC RESISTANCE FOR CONTROL OF FALL ARMYWORM AND CORN EARWORM (LEPIDOPTERA: NOCTUIDAE) ON CORN

Fall armyworm, Spodoptera frugiperda (J. E. Smith), and corn earworm, Helicoverpa zea Boddie, perennially cause leaf and ear damage to corn in the southeastern USA. Development of transgenic hybrids expressing insecticidal endotoxin from Bacillus thuringiensis (Bt) offers a new approach to managing these insects in field corn. Transgenic Bt hybrids with either the Bt11 or MON810 event, collectively known as YieldGard Technology, were evaluated for control fall armyworm and corn earworm in southern Georgia during 1998, which coincided with a severe outbreak of fall armyworm. YieldGard Bt resistance consistently reduced whorl infestation and damage to low levels and also reduced ear infestations and larval numbers per ear. However, larval establishment did occur on many ears of resistant plants, but once established in ears, larvae of both species developed more slowly and caused much less kernel damage on resistant than susceptible plants. We found no relationship between YieldGard Bt resistance and corn grain aflatoxin concentrations. Yield responses were variable with the prevention of yield loss being proportional to the severity of insect damage. These results indicate that YieldGard resistance is effective in preventing significant losses to field corn by fall armyworm and corn earworm. Further, evaluation under a variety of growing conditions and insect infestation levels is needed to clearly assess the value of YieldGard technology to corn growers in the Southeast.

From Asian curiosity to eruptive American pest: Megacopta cribraria (Hemiptera: Plataspidae) and prospects for its biological control

The kudzu bug or bean plataspid, Megacopta cribraria (Fabricius), is native to Asia where it appears to be widely distributed (although the taxonomy is not entirely clear), but is infrequently a pest of legumes. This bug appeared in 2009 in the southeastern United States, where it is closely associated with kudzu, Pueraria montana Lour. [Merr.] variety lobata [Willd.] Maesen & S. Almeida. However, the insect has become a consistent economic pest of soybeans, Glycine max (L.) Merr., and some other leguminous crops in areas where large numbers can build in kudzu, in addition to being a considerable nuisance in urban landscapes where kudzu occurs. The insect has remarkable capacity for movement and has spread rapidly from nine Georgia counties in 2009 to seven states in 2012. Despite being a nuisance in urban areas and a crop pest, high populations of the bug also reduce the biomass of kudzu, which is itself a seriously problematic invasive weed, complicating the status of M. cribraria in its expanded range. Extant predators and a pathogen in the US have been observed attacking kudzu bugs in the laboratory and field, but no parasitism of eggs or nymphs has been observed to date. A single record of parasitism of an adult kudzu bug by a tachinid fly is known from the US, but no other adult parasitism has been observed in the US or elsewhere. Extant enemies may eventually significantly reduce the bug’s populations, but at present native enemies appear to be insufficient for the task, and exotic enemies from the kudzu bug’s native range may offer the best possibility for effective biological control in the US. Based on the available literature, the best option for an importation biological control program appears to be the platygastrid egg parasitoid Paratelenomus saccharalis (Dodd) because of its apparent host specificity, intimate biological linkages with M. cribraria, and wide geographic distribution in the Eastern Hemisphere. Other natural enemies may eventually emerge as good candidates for importation, but at present P. saccharalis appears to be the most promising.

Corn Expressing Cry1ab or Cry1f Endotoxin for Fall Armyworm and Corn Earworm (Lepidoptera: Noctuidae) Management in Field Corn for Grain Production

Abstract Fall armyworm, Spodoptera frugiperda (J. E. Smith), and corn earworm, Helicoverpa zea (Boddie), perennially cause leaf and ear damage to corn in the southeastern United States. Transgenic hybrids expressing the Cry1Ab (MON810 event) or Cry 1F (TC1507 event) insecticidal endotoxin from Bacillus thuringiensis (Bt) were evaluated for management of fall armyworm and corn earworm in central Georgia during 2006 and 2007. Corn was planted at the recommended time in mid-Apr and in late Jun to simulate a double-crop corn planting. Both Bt events reduced whorl infestation and damage by fall armyworm, but TC1507 provided greater protection from whorl injury than MON 810 under severe fall armyworm infestations. Hybrids with the MON810 event usually had less ear infestation by corn earworm than susceptible hybrids, whereas the TC1507 event usually did not reduce ear infestations. Nevertheless, both events prevented ear damage, but there was no consistent difference between the two Bt traits in preventing ear damage. Bt traits did not affect grain yield in either year during the first planting when fall armyworm infestations were low. Both events prevented significant yield loss during the second planting in 2006 when whorl infestation levels exceeded 50% in susceptible hybrids. Because of the greater activity in preventing whorl damage by fall armyworm, the TC1507 event would be useful in mitigating the risk of severe lepidopteran damage to later plantings of field corn for grain production in the southeastern U.S.

Plant-Incorporated Bacillus thuringiensis Resistance for Control of Fall Armyworm and Corn Earworm (Lepidoptera: Noctuidae) in Corn

Abstract Fall armyworm, Spodoptera frugiperda (J.E. Smith), and corn earworm, Helicoverpa zea (Boddie), perennially cause leaf and ear damage to corn, Zea mays L., in the southeastern United States. Transgenic Bacillus thuringiensis (Bt) hybrids with the Bt11, MON810, or 176 events expressing the Cry1Ab insecticidal endotoxin from were evaluated for control fall armyworm and corn earworm at seven locations in Georgia during 1999 and 2000. Corn was planted at the recommended time for each location and 1 and 2 mo later in the southern locations. All Bt events consistently reduced whorl infestation and damage, although event 176 did not prevent whorl damage in the later plantings in the southern locations in both years. All events also reduced seedling damage by the lesser cornstalk borer, Elasmopalpus lignosellus (Zeller), in one trial and stalk infestations and tunnel length by southwestern corn borers, Diatraea grandiosella Dyar, in another trial. Hybrids containing Bt11 and MON810 events reduced ear infestations in all trials, although reductions were small in later plantings. Nevertheless, both events reduced grain damage from earworms and armyworms by an average ± SE of 52.5 ± 5.1% in all trials. The hybrid containing event 176 did not reduce ear infestations and damage. Total grain aflatoxin concentrations were not significantly affected by Bt resistance in any trial (N = 17). Yield responses were variable with the prevention of yield loss being proportional to the severity of insect damage. Although plantings made after the recommended time did not consistently benefit from Bt resistance, Bt11 and MON810 events were effective in reducing damage to field corn when large infestations occurred. The Bt11 and MON810 events mitigated the risk of severe lepidopteran damage to corn, thereby making later plantings of corn feasible in double-cropping systems.

Physiological, nutritional, and biochemical bases of corn resistance to foliage-feeding fall armyworm.

Three corn (Zea mays) germplasm lines [i.e., Ab24E (susceptible control), Mp708 (resistant control), and a locally selected partial inbred line FAW7050 (resistant)] were examined for Spodoptera frugiperda (J.E. Smith; Lepidoptera: Noctuidae) resistance. Nutritional [i.e., total protein content, amino acids, glucose, total nonstructural carbohydrates (TNC), protein to TNC (P/C) ratios] and biochemical (i.e., peroxidase and lipoxygenase 3) properties in the seedlings of these corn lines were examined to categorize resistance mechanisms to S. frugiperda. Physiological changes in photosynthetic rates also were examined in an attempt to explain nutritional and biochemical dynamics among corn germplasm lines and between insect-infested and noninfested corn plants within a germplasm line. Results indicated that S. frugiperda larvae survived better and developed faster in susceptible Ab24E than in resistant FAW7050 or Mp708. The three germplasm lines differed in resistance mechanisms to S. frugiperda, and the observed patterns of resistance were probably collective results of the P/C ratio and defensive proteins. That is, the susceptibility of Ab24E to S. frugiperda was due to a high P/C ratio and a low level of induced defensive compounds in response to insect herbivory, while the resistance of FAW7050 resulted from elevated defensive proteins following insect herbivory, low P/C ratio, and elevated defensive proteins in Mp708 contributed to its resistance to S. frugiperda. The elevated protein amounts in resistant Mp708 and FAW7050 following S. frugiperda injury were likely due to greater conversion of photosynthates to defensive proteins following the greater photosynthetic rates in these entries. Greater photosynthetic capacity in Mp708 and FAW7050 also led to higher amino acid and glucose contents in these two lines. Neither amino acid nor lipoxygenase 3 played a critical role in corn resistance to S. frugiperda. However, high inducibility of peroxidase may be an indicator of S. frugiperda susceptibility as observed elsewhere.

Confirmed Distribution and Occurrence of Megacopta cribraria (F.) (Hemiptera: Heteroptera: Plataspidae) in the Southeastern United States

Abstract Megacopta cribraria (F) (Hemiptera: Heteroptera: Plataspidae) was first discovered in North America in 9 counties in northeastern Georgia (USA) in October 2009. By the end of 2012, surveys conducted in Georgia and neighboring states confirmed that the insect had spread into 383 additional counties in the southeastern U.S., including the states of Alabama, Florida, Georgia, Mississippi, North Carolina, South Carolina, Tennessee and Virginia. It was reported from 33 species of plants representing 15 taxonomic families in these surveys, with 17 of those from the family Fabaceae (legumes). Kudzu (Pueraria montana Lour. [Merr.] variety lobata [Willd.] Maesen & S. Almeida) was the most frequently reported host. All life stages of the insect were observed only on kudzu and soybean (Glycine max [L.] Merrill) which, to date, are the only confirmed reproductive host plants of M. cribraria in its expanded North American range.

Virulence in Hessian fly (Diptera: Cecidomyiidae) field collections from the southeastern United States to 21 resistance genes in wheat.

ABSTRACT Genetic resistance in wheat, Triticum aestivum L., is the most efficacious method for control of Hessian fly, Mayetiola destructor (Say) (Diptera: Cecidomyiidae). However, because of the appearance of new genotypes (biotypes) in response to deployment of resistance, field collections of Hessian fly need to be evaluated on a regular basis to provide breeders and producers information on the efficacy of resistance (R) genes with respect to the genotype composition of Hessian fly in regional areas. We report here on the efficacy of 21 R genes in wheat to field collections of Hessian fly from the southeastern United States. Results documented that of the 21 R genes evaluated only five would provide effective protection of wheat from Hessian fly in the southeastern United States. These genes were H12, H18, H24, H25, and H26. Although not all of the 33 identified R genes were evaluated in the current study, these results indicate that identified genetic resistance to protect wheat from Hessian attack in the southeastern United States is a limited resource. Historically, R genes for Hessian fly resistance in wheat have been deployed as single gene releases. Although this strategy has been successful in the past, we recommend that in the future deployment of combinations of highly effective previously undeployed genes, such as H24 and H26, be considered. Our study also highlights the need to identify new and effective sources of resistance in wheat to Hessian fly if genetic resistance is to continue as a viable option for protection of wheat in the southeastern United States.

Impact of Brown Stink Bug (Heteroptera: Pentatomidae) Feeding on Corn Grain Yield Components and Quality

ABSTRACT Brown stink bug, Euschistus servus (Say) (Heteroptera: Pentatomidae), damage on developing corn, Zea mays L., ears was examined in 2005 and 2006 by using eight parameters related to its yield and kernel quality. Stink bug infestations were initiated when the corn plants were at tasseling (VT), mid-silking (R1), and blister (R2) stages by using zero, three, and six in 2005 or zero, one, two, and four bugs per ear in 2006, and maintained for 9 d. The percentage of discolored kernels was affected by stink bug number in both years, but not always affected by plant growth stage. The growth stage effect on the percentage of discolored kernels was significant in 2006, but not in 2005. The percentage of aborted kernels was affected by both stink bug number and plant growth stage in 2005 but not in 2006. Kernel weight was significantly reduced when three E. servus adults were confined on a corn ear at stage VT or R1 for 9 d in 2005, whereas one or two adults per ear resulted in no kernel weight loss, but four E. servus adults did cause significant kernel weight loss at stage VT in 2006. Stink bug feeding injury at stage R2 did not affect kernel damage, ear weight or grain weight in either year. The infestation duration (9 or 18 d) was positively correlated to the percentage of discolored kernels but did not affect kernel or ear weight. Based on the regression equations between the kernel weight and stink bug number, the gain threshold or economic injury level should be 0.5 bugs per ear for 9 d at stage VT and less for stage R1. This information will be useful in developing management guidelines for stink bugs in field corn during ear formation and early grain filling stages.