J. W. Van Duyn

Comparative production of Helicoverpa zea (Lepidoptera: Noctuidae) from transgenic cotton expressing either one or two Bacillus thuringiensis proteins with and without insecticide oversprays

Abstract Transgenic cotton, Gossypium hirsutum (L.), expressing either one or two Bacillus thuringiensis ssp. kurstaki Berliner (Bt) proteins was compared with the conventional sister line in field experiments with regard to production of bollworm, Helicoverpa zea (Boddie), and bolls damaged by bollworm. The relative numbers of bollworms that developed on Bollgard (Monsanto Co., St. Louis, MO), Bollgard II (Monsanto Co.), and conventional cotton were estimated under nontreated conditions in 2000 and both insecticide-treated and nontreated conditions in 2001–2002 in North Carolina tests. Averaged across seven field studies under nontreated conditions, Bollgard cotton generated statistically similar numbers of large (L4–L5) bollworm larvae compared with the conventional variety; however, Bollgard cotton produced significantly fewer damaged bolls and bollworm adults than the conventional variety. Production of large larvae, damaged bolls, and adults was decreased dramatically by Bollgard II cotton as compared with Bollgard and conventional varieties. When comparing insecticide-treated and nontreated cotton genotypes, both Bt cotton sustained less boll damage than the conventional variety averaged across insecticide regimes; furthermore, Bollgard II cotton had fewer damaged bolls than the Bollgard variety. When averaged across cotton genotypes, pyrethroid oversprays reduced the numbers of damaged bolls compared with the nontreated cotton. Insecticide-treated Bollgard cotton, along with insecticide-treated and nontreated Bollgard II cotton reduced production of bollworm larvae, pupae, and adults. However, the addition of pyrethroid oversprays to Bollgard II cotton seemed to be the best resistance management strategy available for bollworm because no bollworms were capable of completing development under these conditions.

Cross-Resistance Responses of Cry1Ac-Selected Heliothis virescens (Lepidoptera: Noctuidae) to the Bacillus thuringiensis Protein Vip3A

Abstract One susceptible and three Cry1Ac-resistant strains of tobacco budworm, Heliothis virescens (F.) (Lepidoptera: Noctuidae), were used in laboratory studies to determine the level of cross-resistance between the Bacillus thuringiensis (Berliner) toxins Cry1Ac and Vip3A by using concentration–mortality and leaf tissue experiments. Concentration–mortality data demonstrated that the three Cry1Ac-resistant H. virescens strains, YHD2, KCBhyb, and CxC, were at least 215- to 316-fold resistant to Cry1Ac compared with the susceptible strain, YDK. Results from Vip3A concentration–mortality tests indicated that mortality was similar among all four H. virescens strains. Relative larval growth on Cry1Ac reflected concentration–mortality test results, because YHD2 larval growth was mostly unaffected by the Cry1Ac concentrations tested. Growth ratios for KCBhyb and CXC indicated that they had a more moderate level of resistance to Cry1Ac than did YHD2. Relative larval growth on Vip3A was highly variable at lower concentrations, but it was more consistent on concentrations of Vip3A above 25 &mgr;g/ml. Differences in larval growth among strains on Vip3A were not as pronounced as seen in Cry1Ac experiments. Mortality and larval growth also was assessed in leaf tissue bioassays in which YDK, CxC, and KCBhyb neonates were placed onto leaf disks from non-Bt and Bt cotton, Gossypium hirsutum L., for 5 d. Three Bt lines were used in an initial bioassay and consisted of two Vip3A-containing lines, COT203 and COT102, and a Cry1Ac-producing line. Mortality of KCBhyb and CXC was lower than that of YDK larvae in the presence of leaf tissue from the Cry1Ac-producing line. Additionally, increased larval growth and leaf tissue consumption on Cry1Ac-containing leaf disks was observed for KCBhyb and CXC. Mortality and larval weights were similar among strains when larvae were fed leaf tissue of either non-Bt, COT203, or COT102. A subsequent leaf tissue bioassay was conducted that evaluated four cotton lines: non-Bt, Cry1Ab-expressing, Vip3A-expressing, and pyramided-toxin plants that produced both Cry1Ab and Vip3A. Mortality levels were similar among strains when fed non-Bt, Vip3A-expressing, or pyramided-toxin leaf tissues. Mortality was higher for YDK than for KCBhyb or CXC on Cry1Ab-expressing leaf tissues. No differences in larval weights were observed among strains for any genotype tested. Results of these experiments demonstrate that cross-resistance is nonexistent between Cry1Ac and Vip3A in H. virescens. Thus, the introduction of Vip3A-producing lines could delay Cry1Ac-resistance evolution in H. virescens, if these lines gain a significant share of the market.

Regional assessment of Helicoverpa zea populations on cotton and non-cotton crop hosts

Selection pressure on bollworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), by cotton, Gossypium hirsutum (L.) (Malvaceae), that produces one or more Bacillus thuringiensis Berliner (Bt) proteins is reduced by plantings of non‐Bt refuge cotton that produce non‐selected individuals. However, the contributions of non‐Bt, non‐cotton crop hosts to the overall effective refuge for H. zea on Bt cotton have not been estimated. A 2‐year, season‐long study was conducted in five US cotton‐producing states to assess the spatial and temporal population dynamics and host use of H. zea. Helicoverpa zea larval estimates in commercial crop fields demonstrated that non‐cotton crop hosts, such as maize, Zea mays L. (Poaceae), grain sorghum, Sorghum bicolor (L.) Moench (Poaceae), peanut, Arachis hypogaea L. (Fabaceae), and soybean, Glycine max (L.) Merrill (Fabaceae), collectively support much larger larval populations than cotton throughout the season. Larval populations were almost entirely restricted to maize in the middle part of the season (June and portions of July), and were observed in non‐cotton crop hosts more frequently and typically in larger numbers than in cotton during the period when production would be expected in cotton (July and August). Numbers of H. zea larvae produced in replicated strip trials containing various crop hosts paralleled production estimates from commercial fields. In contrast, the number of H. zea adults captured in pheromone traps at interfaces of fields of Bt cotton and various crop hosts rarely varied among interfaces, except in instances where maize was highly attractive. With the exception of this early season influence of maize, moth numbers were not related to local larval production. These data demonstrate that H. zea adults move extensively from their natal host origins. Therefore, non‐cotton crop hosts, and even relatively distant hosts, contribute significantly to effective refuge for H. zea on Bt cotton. The results presented here demonstrate that substantial natural refuge is present for Bt‐resistance management of H. zea throughout the mid‐South and Southeast portions of the US cotton belt.

Quantification of Cry1Ac and Cry1F Bacillus thuringiensis Insecticidal Proteins in Selected Transgenic Cotton Plant Tissue Types

ABSTRACT Quantitative enzyme-linked immunosorbent assays were used to characterize the geographical (locations) and temporal (through 6 wk) expression of Cry1Ac, from Bacillus thuringiensis variety kurstaki, and Cry1F, from B. thuringiensis variety aizawai, in transgenic cotton, Gossypium hirsutum L., plant structures. Terminal leaves, squares (flower buds), flowers, bolls (fruit), and mature leaves located five and eight nodes below the terminal apex were sampled during weeks 2, 4, and 6 after the initiation of anthesis. The effect of location (environment) significantly influenced protein expression levels, although similar trends were observed across locations. Cry1F was expressed at levels greater (1.1-29.0-fold) than that for Cry1Ac in all structures with exception to flowers. In contrast, the level of Cry1Ac in flowers was generally greater than Cry1F. Within each sampling period, concentrations of Cry1F in mature leaves (five and eight node) were greater than that for other structures. Expression was also greater for older, eight-node mature leaves than younger, five-node mature leaves. Cry1Ac expression in bolls was lowest compared with terminal leaves, squares, flowers, and mature leaves, which expressed at similar concentrations. Cry1F expression increased through time for mature leaves and terminal leaves; whereas, a decline in Cry1Ac protein concentration was observed for terminal leaves and bolls. The data presented here provides a means to understand observed levels of efficacy (patterns of insect damage) by comparing the spatial and temporal dynamics of expression for Cry1Ac and Cry1F in PhytoGen 440W transgenic cotton.

Evaluation of corn hybrids expressing Cry1F (Herculex® I Insect Protection) against fall armyworm (Lepidoptera: Noctuidae) in the southern United States

Efficacy of two insect-resistant corn hybrids expressing the Cry1 F insecticidal crystal protein of Bacillus thuringiensis var. aizawai Berliner (transformation event TC1507) was evaluated against fall armyworm, Spodoptera frugiperda (J.E. Smith), in three southern U.S. locations. Larval susceptibility was evaluated on CrylF and nonBt field corn, Zea mays L., plants (V3–V12 and R1–R2 stages) in field plots and laboratory studies. Leaf-feeding injury was significantly less and plant height was significantly greater for hybrids containing Cry1 F as compared with nonBt corn hybrids when exposed to natural or artificial fall armyworm infestations. In addition, larval mortality was significantly greater on CrylF corn hybrids compared with that on nonBt hybrids. These results demonstrate that corn hybrids containing CrylF represent an effective plant incorporated insecticidal protein management option for fall armyworm. In environments where fall armyworm may exceed damage thresholds and have to be carefully ma...

Relationship Between Cereal Leaf Beetle (Coleoptera: Chrysomelidae) Egg and Fourth-Instar Populations and Impact of Fourth-Instar Defoliation of Winter Wheat Yields in North Carolina and Virginia

Abstract Cereal leaf beetle, Oulema melanopus (L.), has become a serious pest of small grains in the mid-Atlantic region of the United States. Existing thresholds for implementing control measures allowed too much leaf damage and consequent yield loss to occur before recommending treatment. Information on beetle biology and crop response to injury, both prerequisites for developing new management strategies, was lacking for this region. A 3-yr project was initiated to generate an area wide cereal leaf beetle biological and yield impact database for winter wheat, and to evaluate the injury and yield loss potential of different population densities. Over the study period, beetle populations were evaluated at 26 winter wheat field locations in Virginia and North Carolina. Eggs and larvae, classified to instar, were counted twice each week from February to June. Replicated insecticide versus noninsecticide treatments were conducted at each location where leaf defoliation and yield were documented. Results showed that the relationship between 50th percentile egg and fourth-instar population estimates were in strong agreement (y = 0.36x − 0.01; r2 = 0.79). Potentially detrimental larval infestations were forecast before appearance of foliage injury from egg populations present during the stem elongation to flag leaf emergence developmental stages. A significant positive linear relationship between total fourth instar per stem population estimates and percent flag leaf defoliation was detected (y = 20.29x + 1.34; r2 = 0.60). A weaker but still significant relationship between the total fourth-instar population estimates and percent yield loss was found (y = 11.74x + 6.51; r2 = 0.26), indicating that factors in addition to flag leaf injury, primarily by fourth instars, also contributed to reduced yields.

Efficacy of Transgenic Cotton Expressing Cry1Ac and Cry1F Insecticidal Protein Against Heliothines (Lepidoptera: Noctuidae)

Abstract Cotton, Gossypium hirsutum L, plants expressing Cry1Ac and Cry1F (Phytogen 440W) insecticidal crystal proteins of Bacillus thuringiensis (Bt) Berliner, were evaluated against natural populations of tobacco budworm, Heliothis virescens (F.), and bollworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), across 13 southern U.S. locations that sustained low, moderate, and high infestations. The intrinsic activity of Phytogen 440W was compared with nontreated non-Bt cotton (PSC355) and with management strategies in which supplemental insecticides targeting heliothines were applied to Phytogen 440W and to PSC355 cotton. Infestations were composed primarily of bollworm, which is the least sensitive of the heliothine complex to Cry toxins. Therefore, damage recorded in these studies was primarily due to bollworm. Greater than 75% of all test sites sustained heliothine infestations categorized as moderate to high (10.6–64.0% peak damaged bolls in nontreated PSC355). Phytogen 440W, alone or managed with supplemental insecticide applications, reduced heliothine-damaged plant terminals, squares (flower buds), flowers, and bolls equal to or better (1.0–79.0-fold) than managing a non-Bt cotton variety with foliar insecticides across all infestation environments. Rarely (frequency of ≤11% averaged across structures), sprayed Phytogen 440W reduced damaged structures compared with nontreated Phytogen 440W. Protection against heliothine-induced plant damage was similar across the three levels of infestation for each viable management strategy, with exception to damaged squares for nontreated Phytogen 440W. In situations of moderate to high heliothine infestations, cotton plants expressing Cry1Ac and Cry1F may sustain higher levels of damage compared with that same variety in low infestations. No significant difference in yield was observed among heliothine management strategies within each infestation level, indicating cotton plants may compensate for those levels of plant damage. These findings indicate Phytogen 440W containing Cry1Ac and Cry1F provided consistent control of heliothines across a range of environments and infestation levels.

Population consequences of diapause in a model system: the European corn borer.

The diapause biology of the European corn borer (ECB), Ostrinia nubilalis (Hübn.), is described based on natural and controlled environment studies of feral and lab‐reared ECBs in North Carolina (NC). The diapause response is described as a function of photophase (h of light/day) as well as a function of larval age (instar) at onset of diapause‐inducing conditions. A critical photophase of 14.4 h and a critical mean larval instar of 3.3 is found in the lab studies and supported by three years of insectary studies. Seven years of black light trapping of ECB moths in Goldsboro, NC, revealed the likelihood of up to four moth flights/year.

Effect of insecticide treatments and environmental factors on thrips populations, plant growth and yield of cotton.

Field experiments were conducted in 1997–1999 in Washington Co., NC, to examine how cotton, Gossypium hirsutum, is affected by thrips species composition and abundance, environmental factors, and i...

Effect of Disk Harrowing on Subsequent Emergence of Hessian fly (Diptera: Cecidomyiidae) Adults from Wheat Stubble

Conical cloth traps were used to compare emergence of Hessian fly, Mayetiola destructor (Say), adults from three land preparation regimes: 1) wheat stubble disked; 2) stubble not disked, but burned; 3) stubble neither disked nor burned (control). Burning had no effect on emergence in the one experiment in which it was tested. Mean emergence in disked plots was approx. 60% less than in control plots. However, this difference was significant in only one of four experiments. Implications for Hessian fly management within a wheat-soybean double-cropping system are discussed.