Frequency and severity of western bean cutworm (Lepidoptera: Noctuidae) ear damage in transgenic corn hybrids expressing different Bacillus thuringiensis cry toxins

The frequency and severity of corn ear damage caused by western bean cutworm, Striacosta albicosta (Smith), were measured on transgenic corn, Zea mays L., hybrids expressing two different insecticidal Bacillus thuringiensis (Bt) (Berliner) Cry toxins (Bt) selected to protect against damage caused by larval European corn borer, Ostrinia nubilalis (Hübner). A field cage experiment deliberately infested with western bean cutworm egg masses resulted in less damage in the hybrid expressing the Cry1F protein and supported fewer western bean cutworm larvae than its non-Bt isoline. Corn hybrids expressing Cry1F, grown in small plot field experiments at three locations over two separate years and exposed to natural western bean cutworm infestations suffered less damage than non-Bt or Bt-hybrids expressing a Cry1Ab protein. Later maturing hybrids suffered more damage than shorter-season hybrids. Finally, corn ears observed in strip trials for several years in diverse agronomic conditions in farmer-cooperator fields corroborated the in-plant protection conferred by corn hybrids expressing the Cry1F protein in small plot field trials.     

Cannibalism of Helicoverpa zea (Lepidoptera: Noctuidae) from Bacillus thuringiensis (Bt) transgenic corn versus non-Bt corn

Because of the importance of cannibalism in population regulation of Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) in corn, Zea mays L., it is useful to understand the interactions between Bacillus thuringiensis (Bt) transgenic corn and cannibalism. To determine the effects of Bt corn on cannibalism in H. zea, pairs of the same or different instars were taken from Bt or non-Bt corn and placed on artificial diet in proximity. Cannibalism occurred in 91% of pairs and was approximately 7% greater for pairs of larvae reared from Bt transgenic corn (95%) than from non-Bt corn (88%). Also, first instar by first instar pairs had a lower rate of cannibalism than other pairs. Time until cannibalism was not different for larvae from Bt corn versus non-Bt corn. Pupation rate of cannibals and surviving victims was not different for pairs from Bt corn versus non-Bt corn. Finally, cannibalism increased pupation rate of cannibals from both Bt and non-Bt corn by approximately 23 and 12%, respectively, although the increases were not significant. Thus, negative effects of Bt on larvae were compensated by increased cannibalism in comparison with larvae reared on non-Bt corn, which increased larval survival to levels comparable with larvae reared on non-Bt plants.     

粘虫高龄幼虫对转Bt基因玉米的消化和利用

在室内用重量法研究了粘虫Mythimna separata (Walker)高龄幼虫对转Bt基因玉米MON810和Bt11叶片的消化和利用,以明确Bt玉米对暴食期幼虫取食的影响。结果表明,在连续测定的5天中,取食MON810和Bt11两种Bt玉米叶片时,幼虫存活率和取食量均显著低于各自的对照组幼虫,取食Bt玉米叶片的幼虫体重呈下降趋势,第3 天时分别比第2 天减少12.2 mg 和7.4 mg,而取食对照玉米叶片时的幼虫日增重显著的高于处理组的幼虫,第3 天的日增重分别为100.4 mg 和119.9 mg。取食Bt玉米叶片的幼虫对食物的转化率(ECI和ECD)均为负值,在最初4 天的ECI和ECD都显著低于对照组幼虫,但取食两种非Bt玉米叶片的幼虫的近似消化率(AD) 随取食时间的延长而逐渐下降,取食第5 天分别为20.6 %和15.1 %;而取食MON810和Bt11叶片时幼虫的AD均显著地高于对照组幼虫。     

Field efficacy of sweet corn hybrids expressing a Bacillus thuringiensis toxin for management of Ostrinia nubilalis (Lepidoptera: Crambidae) and Helicoverpa zea (Lepidoptera: Noctuidae)

Field studies were done in 1995-1996 to assess the efficacy of three sweet corn hybrids that express the Bacillus thuringiensis (Bt) toxin, CrylAb, against two lepidopteran pests, Ostrinia nubilalis (Hubner) and Helicoverpa zea (Boddie). The Bt hybrids tested were developed by Novartis Seeds, using the event BT-11, which expresses Bt toxin in green tissue as well as reproductive tissues including the tassel, silk, and kernel. Bt hybrids were compared with a standard non-Bt control or the non-Bt isoline for each hybrid; none of the hybrids were treated with insecticides during the study. Hybrid efficacy was based on larval control of each pest, as well as plant or ear damage associated with each pest. In both years, control of O. nubilalis larvae in primary ears of all Bt hybrids was 99-100% compared with the appropriate non-Bt check. Plant damage was also significantly reduced in all Bt hybrids. In 1996, control of H. zea in Bt hybrids ranged from 85 to 88% when compared with the appropriate non-Bt control. In 1996, a University of Minnesota experimental non-Bt hybrid (MN2 x MN3) performed as well as the Bt hybrids for control of O. nubilalis. Also, in 1996, two additional University of Minnesota experimental non-Bt hybrids (A684su X MN94 and MN2 X MN3) performed as well as Bt hybrids for percent marketable ears (ears with no damage or larvae). In addition, compared with the non-Bt hybrids, percent marketable ears were significantly higher for all Bt hybrids and in most cases ranged from 98 to 100%. By comparison, percent marketable ears for the non-Bt hybrids averaged 45.5 and 37.4% in 1995 and 1996, respectively. Results from the 2-yr study strongly suggest that Bt sweet corn hybrids will provide high levels of larval control for growers in both fresh and processing markets. Specifically, Bt sweet corn hybrids, in the absence of conventional insecticide use, provided excellent control of O. nubilalis, and very good control of H. zea. However, depending on location of specific production regions, and the associated insect pests of sweet corn in each area, some insecticide applications may still be necessary.     

Effect of corn hybrids expressing the coleopteran-specific cry3Bb1 protein for corn rootworm control on aboveground insect predators

Field and laboratory studies were conducted to determine the effect of transgenic Bacillus thuringiensis (Bt) corn, Zea mays L. (YieldGard Rootworm), expressing the Cry3Bb1 protein on aboveground nontarget insect predators (minute pirate bug, ladybird beetles, and carabids). Visual counts of adult and immature Orius insidiosus (Say), Coleomegilla maculata (DeGeer), Hippodamia convergens Gurin-Meneville, and Scymnus spp. occurring in Bt corn and its non-Bt isoline were made at Manhattan, KS, in 2002 and at Manhattan and Scandia, KS, in 2003. No significant differences were found between the Bt corn and non-Bt isoline plots in the abundance (number per plant) of O. insidiosus, C. maculata, H. convergens, and Scymnus spp. Field predation on Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae) egg masses was also observed during the silking stage of corn at Manhattan and Scandia in 2003. No significant differences were observed among treatments in predation rate for predators with chewing versus sucking mouthparts. Two laboratory studies determined the effect of Cry3Bb1 protein expressed in Bt corn pollen on C. maculata and carabids. The larvae of C. maculata were reared on Bt pollen, non-Bt pollen, or greenbugs, Schizaphis graminum (Rondani). The duration of larval and pupal stages, developmental time from egg hatch to adult emergence, percentage of survival, and elytra length were compared among treatments. There were no significant differences in developmental time of larvae fed pollen or greenbugs during their first two instars. However, significantly prolonged development of the third (1 d) and fourth instars (2 d) was observed for larvae fed greenbugs only. Total time for larval development was significantly longer for larvae that fed on greenbugs versus larvae fed on pollen. No significant differences were observed among treatments in the percentage of larvae that pupated or pupal stage duration. Larvae that fed on greenbugs had higher pupal and adult weights compared with pollen-fed larvae. However, pupal and adult weights did not vary between the Bt and non-Bt pollen treatments. No significant differences occurred in longevity and elytra length of beetles among all treatments. Two carabid species, Harpalus caliginosus F. and Harpalus pensylvanicus DeGeer, were reared on moistened dog food sprinkled with Bt or non-Bt corn pollen. No significant differences in mortality of H. caliginosus and H. pensylvanicus were detected among any of the treatments. There was no significant effect of Bt pollen on fecundity and egg viability of H. caliginosus. Our studies showed that YieldGard Rootworm had no effect on the selected coleopteran predators; therefore, this Bt corn hybrid could be used in an integrated pest management system.     

Effects of MON810 Bt field corn on adult emergence of Helicoverpa zea (Lepidoptera: Noctuidae)

A 3-yr study (1996-1998) was conducted to evaluate the effects of MON810 Bt corn on Helicoverpa zea (Boddie) emergence and to determine whether delayed larval development as a result of Bt intoxication results in higher levels of diapause induction and pupal mortality. In the 1997 study, there was no difference in prepupal mortality between corn types, although significantly more prepupae from Bt plots than from non-Bt plots died in emergence buckets before constructing pupal chambers in 1998. In all years, significantly fewer moths emerged from prepupae collected from Bt plots, suggesting that effects of the expressed Cry1Ab extended to the prepupal and pupal stages. Late plantings of corn showed the greatest reductions in moth emergence from Bt corn because environmental conditions were more conducive to trigger diapause at the time H. zea was developing in these plantings. This was supported by a significantly greater proportion of diapausing pupae remaining in the ground in the late plantings of both Bt and non-Bt corn. For April and early May plantings, larval feeding on Bt corn delayed the time to pupation, although there was no significant difference in moth emergence between corn types for those larvae that successfully pupated. Although Bt expression had less impact on the proportion of moths emerging, the actual number of moths emerging from Bt corn was significantly reduced because fewer larvae reached pupation. Delays in adult emergence, along with significant reductions in adult emergence from MON810 Bt corn, should reduce the rates of colonization in soybean and other late host crops but may also result in asynchrony of mating between individuals emerging from Bt and non-Bt corn. This, in turn, may contribute to the evolution of resistance to Bt corn.     

Influence of plant severing on movement of Ostrinia nubilalis larvae in Zea mays hybrid seed production fields

Genetically engineered corn hybrids that contain a cry gene from the bacterium Bacillus thuringiensis Berliner (Bt) are gaining popularity for controlling the corn pest Ostrinia nubilalis (Hübner). Continuous use of Bt corn, however, could select for O. nubilalis that are resistant to this corn. Monitoring for insect resistance is important, because it could help maintain the Bt technology. A possible monitoring method is to collect larval insects in commercial drying bins after harvest from Bt seed production fields. A drawback to this method is that these collections may be contaminated by insects that moved as later instars from severed non-Bt male rows into the adjacent Bt female rows. These larvae have little to no exposure to Bt toxin, resulting in possible "false positives." The objectives of this study were to first find which combination of planting and severing dates produces the least number of larvae that move from non-Bt male plants to Bt female plants and to assess O. nubilalis larval movement from severed non-Bt male rows to Bt female rows. Field studies in 2002 and 2003 were designed to simulate a hybrid seed production field. Results suggest that movement of O. nubilalis larvae from male corn is minimized when corn is planted early and male plants are severed by 2 wk post-anthesis. This reduces the likelihood of false positives by reducing the number of susceptible larvae moving between Bt and non-Bt plants. Also, larvae moved to all four female rows that were adjacent to the severed rows, but there were significantly more larvae found in the closest row compared with the other three. These results could be used to develop a monitoring program to find O. nubilalis larvae with resistance to Bt corn in field populations of O. nubilalis.     

Cross-pollination of nontransgenic corn ears with transgenic Bt corn: efficacy against lepidopteran pests and implications for resistance management

The efficacy of nontransgenic sweet corn, Zea mays L., hybrids cross-pollinated by Bacillus thuringiensis (Bt) sweet corn hybrids expressing Cry1Ab toxin was evaluated in both field and laboratory studies in Minnesota in 2000. Non-Bt and Bt hybrids (maternal plants) were cross-pollinated with pollen from both non-Bt and Bt hybrids (paternal plants) to create four crosses. Subsequent crosses were evaluated for efficacy in the field against European corn borer, Ostrinia nubilalis (Hübner), and corn earworm, Helicoverpa zea (Boddie), and in laboratory bioassays against O. nubilalis. Field studies indicated that crosses with maternal Bt plants led to low levels of survival for both O. nubilalis and H. zea compared with the non-Bt x non-Bt cross. However, the cross between non-Bt ears and Bt pollen led to survival rates of 43 and 63% for O. nubilalis and H. zea larvae, respectively. This intermediate level of survival also was reflected in the number of kernels damaged. Laboratory bioassays for O. nubilalis, further confirmed field results with larval survival on kernels from the cross between non-Bt ears and Bt pollen reaching 60% compared with non-Bt crossed with non-Bt. These results suggest that non-Bt refuge plants, when planted in proximity to Bt plants, and cross-pollinated, can result in sublethal exposure of O. nubilalis and H. zea larvae to Bt and may undermine the high-dose/refuge resistance management strategy for corn hybrids expressing Cry1Ab.     

转Bt基因玉米对甜菜夜蛾幼虫存活和发育的影响

在室内测定了2种转Cry1Ab基因的Bt玉米MON810和Bt11不同组织对甜菜夜蛾 Spodoptera exigua （Hübner）初孵幼虫以及心叶对4龄幼虫存活和发育的影响,在田间比较了甜菜夜蛾幼虫取食Bt 和非Bt玉米雌穗的存活和为害情况。结果表明,转Cry1Ab基因的Bt玉米的不同组织对甜菜夜蛾初孵幼虫都具有明显的杀虫活性,取食Bt玉米心叶、苞叶、籽粒时甜菜夜蛾均在幼虫期死亡; 取食MON810和Bt11雄穗的初孵幼虫化蛹率分别为5.2%和2.1%,羽化率为2.1%和1.0%;取食MON810和Bt11花丝的初孵幼虫化蛹率分别为1.0%和2.1%,但不能羽化。4龄幼虫取食MON810玉米心叶的化蛹率与对照差异不显著,而取食Bt11的化蛹率与对照差异显著; 取食两种Bt玉米心叶的４龄幼虫化蛹后的雌、雄蛹重和羽化率与对照组差异显著,但蛹期和平均单雌产卵量差异不显著,虽然对照组羽化的成虫平均产卵量高于Bt玉米组。田间接种初孵幼虫10 天后的调查结果表明,在MON810和Bt11玉米花丝上幼虫存活率分别为1.3%和0.3%, 而对照组分别为12.9%和16.2%;MON810和Bt11玉米雌穗被害率分别为18.3%和5.0%,而对照组分别为93.3%和95.0%,均显著低于对照组。     

Evaluation of transgenic Bacillus thuringiensis corn hybrids against Cry1Ab-susceptible and -resistant sugarcane borer (Lepidoptera: Crambidae)

A Louisiana strain of the sugarcane borer, Diatraea saccharalis (F.) (Lepidoptera: Crambidae), was selected for resistance to the CrylAb protein of Bacillus thuringiensis (Bt) by using an F2 screening procedure. Survival of Bt-resistant, -susceptible, and -heterozygous genotypes of sugarcane borer was evaluated on vegetative and reproductive stages of five non-Bt and seven Bt field corn, Zea mays L., hybrids in a greenhouse study. Larval survival was recorded 21 d after infestation of neonates on potted plants. Larval survival across the three sugarcane borer genotypes and five non-Bt corn hybrids after 21 d ranged from 23.6 +/- 5.2% (mean +/- SEM) to 57.5 +/- 5.2%. Mean survival of Cry1Ab-resistant larvae on vegetative and reproductive plant stages was 12 and 21%, respectively. During the vegetative stages, all seven Bt corn hybrids were highly efficacious against Cry1Ab-susceptible and -heterozygous genotypes of sugarcane borer, with a larval survival rate of <2% for the Bt-susceptible genotype and < or =5% for the heterozygotes. However, 8-18% of the heterozygous genotype survived on reproductive stage plants for four of the seven Bt corn hybrids tested. The variation in performance of Bt corn cultivars at vegetative and reproductive growth stages against Cry1Ab resistant sugarcane borer suggests differential seasonal expression that may hasten resistance in the field. Bt corn hybrids expressing a "high dose" for European corn borer, Ostrinia nubilalis (Hübner), may not produce a sufficient high dose for the sugarcane borer.     

转Bt基因抗虫玉米对亚洲玉米螟幼虫取食行为的影响

室内研究了转cry1Ab杀虫蛋白基因的Bt抗虫玉米MON81 0和Bt1 1对亚洲玉米螟Ostriniafurnacalis初孵幼虫和3龄幼虫的取食行为、取食选择性和存活率的影响。在48h的非选择性试验中玉米螟初孵幼虫在MON81 0和Bt1 1玉米心叶组织上的幼虫取食率随时间的增加而下降,在对照玉米上的幼虫取食率随时间的增加而上升,两者间差异极显著。初孵幼虫接虫到MON81 0和Bt1 1玉米叶片48h的累计死亡率分别为67 .5 %和47 .5 % ,而在对照玉米上死亡率均为0. 3龄幼虫在Bt和非Bt玉米穗轴组织上的幼虫取食率随时间的增加呈上升趋势,第48h时在Bt和非Bt玉米上的幼虫取食率分别达到77 5 %和1 0 0 % ,差异极显著。选择性试验中,第4～48h内,初孵幼虫在Bt玉米上的幼虫取食率呈下降趋势,第48h时MON81 0和Bt1 1与各自非Bt对照的组合中初孵幼虫的累计死亡率分别为2 5 .0 %和1 7. 5 % ,二者差异不显著。3龄幼虫在Bt玉米和非Bt玉米上的幼虫取食率均随时间的延长而增加,但在非Bt玉米的幼虫取食率增加速度快,与Bt玉米差异极显著。Bt玉米对玉米螟幼虫取食有抑制和忌避作用。     

转 Bt 基因水稻对三化螟自然种群的影响

为了了解水稻重要害虫三化螟 Scirpophaga incertulas（Walker）对转 Bt 基因水稻产生抗性的潜在风险,本文利用自然种群生命表,研究了第 3 代三化螟在转Bt基因杂交稻汕优 63 及非转 Bt 基因杂交稻汕优 63 上的种群参数。结果表明：在 Bt 稻上1～2 龄幼虫的存活率为 4.03%,极显著低于非转基因 SY63（55.76%）;Bt 稻上幼虫为害率为1.75%,极显著低 于非转基因 SY63（5.98%）;Bt 稻上存活的幼虫发育历期明显长于非转 Bt SY63。     

Feeding behavior of neonate Ostrinia nubilalis (Lepidoptera: Crambidae) on Cry1Ab Bt corn: implications for resistance management

The European corn borer, Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae), is an economically important insect pest of corn, Zea mays L., in the United States and Canada. The development of genetically modified corn expressing genes derived from Bacillus thuringiensis (Bt) that encodes insecticidal crystalline (Cry) proteins has proven to be effective in controlling this insect. To assess the feeding behavior of neonate O. nubilalis on Bt corn, we examined differences in feeding behavior, based on presence of plant material in the gut, between Cry1Ab Bt corn and non-Bt near isoline corn for four intervals over a 48-h period. Feeding experiments revealed that there was significantly less feeding on Bt corn compared with non-Bt near isoline corn. The behavior of neonates on the plant corresponded with the differences in feeding on the two corn lines. The findings also showed that > 50% of the larvae initially left the plant before there was evidence in the gut of feeding regardless of whether the source was Bt or non-Bt corn. A higher quantity of plant material was found in the gut of larvae recovered from leaves of non-Bt compared with Bt corn. At the end of 48 h among the larvae that had left the plant, a greater proportion from Bt corn had plant material in the gut than did those from non-Bt corn.     

Effects of bacillus thuringiensis transgenic corn on corn earworm and fall armyworm (Lepidoptera: Noctuidae) densities

We examined 17 pairs of near-isogenic hybrids of Bacillus thuringiensis (Bt) (176, Mon810, and Bt11) and non-Bt corn, Zea mays L., to examine the effects of Bt on larval densities of Helicoverpa zea (Boddie) and Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) during 2 yr. During ear formation, instar densities of H. zea and S. frugiperda were recorded for each hybrid. We found that H. zea first, second, and fifth instar densities were each affected by Mon810 and Bt11 Bt corn but not by 176 corn. Surprisingly, first and second instars were found in higher numbers on ears of Mon810 and Bt11 corn than on non-Bt corn. Densities of third and fourth instars were equal on Bt and non-Bt hybrids, whereas densities of fifth instars were lower on Bt plants. S. frugiperda larval densities were only affected during 1 yr when second, and fourth to sixth instars were lower on ears of Mon810 and Bt11 hybrids compared with their non-Bt counterparts. Two likely explanations for early instar H. zea densities being higher on Bt corn than non-Bt corn are that (1) Bt toxins delay development, creating a greater abundance of early instars that eventually die, and (2) reduced survival of H. zea to later instars on Bt corn decreased the normal asymmetric cannibalism or H. zea-S. frugiperda intraguild predation of late instars on early instars. Either explanation could explain why differences between Bt and non-Bt plants were greater for H. zea than S. frugiperda, because H. zea is more strongly affected by Bt toxins and more cannibalistic.     

Effect of planting dates and Bacillus thuringiensis corn on the population dynamics of European corn borer (Lepidoptera: Crambidae).

Field studies were conducted to determine how field corn, Zea mays L., phenologies in combination with transgenic Bacillus thuringiensis Berliner (Bt) corn and non-Bt (near isogenic) corn could affect egg laying by female European corn borer, Ostrinia nubilalis (Hubner), and subsequent larval injury. Transgenic Bt (events 176 and Bt11) and non-Bt corn was planted at three different times to assess the use of early- and late- planted Bt corn as a means for egg recruitment to these targeted planting dates. Plant growth stages, egg densities, and stalk tunneling was recorded at four locations in southwestern, central, and northern Iowa for three summers (1996-1998). No significant differences in egg densities were observed between Bt and non-Bt corn during the first and second generation for all three years. Significant differences did occur among planting dates. Between 50 and 100% of the eggs were laid in the early planting during the first generation. In addition, between 40 and 65% of the eggs were laid in the late planting for the second generation. Correlations between egg density and larval tunneling were inconsistent from year to year. Additional inconsistencies stemming from yearly phenological differences among sequential plantings and variable O. nubilalis populations increases the difficulty in recommending planting date adjustments as a practical management tool for European corn borer and Bt corn.     

Evaluation of transgenic Bt corn for resistance to the Asian corn borer (Lepidoptera: Pyralidae)

The Asian corn borer, Ostrinia furnacalis (Guenée), is the most important insect pest on corn in China. Bt transgenic corn provides a new tool for Asian corn borer control. Monsanto's YieldGard Bt transgenic corn expressing Cry1Ab protein, and a non-Bt control, were evaluated in Beijing. Laboratory bioassays were carried out by exposing neonates to an agar-free diet containing Bt corn whorl leaves, tassels, and anthers, or by exposing neonates directly to fresh silk and pollen. These are the tissues initially attacked by neonates in the field. All of these tissues, with the exception of pollen, contained sufficient insecticidal protein to kill > or = 95% of larvae within 7 d. Surviving larvae had also not grown beyond first instar and weighed < or = 0.1 mg. Although larvae feeding on Bt corn pollen were significantly smaller than those on non-Bt corn pollen, there was no significant difference in mortality. Field trials were also conducted with artificial infestations of Asian corn borer at mid whorl, late whorl, and silking stages. Damage ratings and number of larvae surviving per plant indicated that Bt corn was highly resistant to Asian corn borer. Therefore, YieldGard offers the potential for season-long protection against first- and second-generation Asian corn borer.     

新疆棉区转Bt基因棉对棉铃虫生物学的影响

棉铃虫Helicoverpaarmigera高龄幼虫取食转Bt基因棉花组织后 ,化蛹率、羽化率、蛹重、体长均有显著下降 ,在转Bt基因棉花上棉铃虫的取食行为也受到较大的影响 ,表现为取食次数明显减少、吐丝下垂次数明显增加 ;无论是转Bt基因棉花还是常规棉花 ,棉铃虫 3龄幼虫主要分布于繁殖器官上 ,在转Bt基因棉花各繁殖器官上的分布概率为 :花 >棉铃 >棉蕾 ,常规棉花上分布概率为 :棉蕾 >棉铃 >花 ;棉铃虫高龄幼虫取食转Bt基因棉花各组织 ,成虫羽化后产卵量、卵孵化率均有明显下降 ;在较低的棉铃虫虫口密度下 ,转Bt基因棉花对棉铃虫有一定的产卵排趋性。     

Development,survival and fitness performance of Helicoverpa zea (Lepidoptera: Noctuidae) in MON810 Bt field corn

Helicoverpa zea (Boddie) development, survival, and feeding injury in MON810 transgenic ears of field corn (Zea mays L.) expressing Bacillus thuringiensis variety kurstaki (Bt) Cry1Ab endotoxins were compared with non-Bt ears at four geographic locations over two growing seasons. Expression of Cry1Ab endotoxin resulted in overall reductions in the percentage of damaged ears by 33% and in the amount of kernels consumed by 60%. Bt-induced effects varied significantly among locations, partly because of the overall level and timing of H. zea infestations, condition of silk tissue at the time of egg hatch, and the possible effects of plant stress. Larvae feeding on Bt ears produced scattered, discontinuous patches of partially consumed kernels, which were arranged more linearly than the compact feeding patterns in non-Bt ears. The feeding patterns suggest that larvae in Bt ears are moving about sampling kernels more frequently than larvae in non-Bt ears. Because not all kernels express the same level of endotoxin, the spatial heterogeneity of toxin distribution within Bt ears may provide an opportunity for development of behavioral responses in H. zea to avoid toxin. MON810 corn suppressed the establishment and development of H. zea to late instars by at least 75%. This level of control is considered a moderate dose, which may increase the risk of resistance development in areas where MON810 corn is widely adopted and H. zea overwinters successfully. Sublethal effects of MON810 corn resulted in prolonged larval and prepupal development, smaller pupae, and reduced fecundity of H. zea. The moderate dose effects and the spatial heterogeneity of toxin distribution among kernels could increase the additive genetic variance for both physiological and behavioral resistance in H. zea populations. Implications of localized population suppression are discussed.     

Effects of transgenic bt corn on growth and development of the stalk borer Papaipema nebris (Lepidoptera: Noctuidae)

This study assessed the efficacy of two different genetic events, event Bt 11 (CrylAb) and event CBH351 (Cry 9C), in Bt corn against two instar classes of the stalk borer Papaipema nebris across three different plant stages (V1, V3, and V5) of corn, Zea mays. Class A includes instars 1 and 2, and class B includes instars 3 and 4. Stalk borer response and development over time were measured, and the data from 1999 and 2000 show that the Bt corn does have some effect on the feeding and development of P. nebris. Injury to the corn plant was reduced, although not eliminated. Stalk borer larvae caused significantly (P = 0.0001) more injury to the non-Bt plants than to the Bt plants over time. Growth and development of the larvae were slowed and mortality was higher for Bt corn than for non-Bt corn. These data suggest that planting Bt corn may benefit growers by reducing, but not eliminating, stalk borer infestations and subsequent plant injury.     

Dusky sap beetles (Coleoptera: Nitidulidae) and other kernel damaging insects in Bt and non-Bt sweet corn in Illinois

Bt and non-Bt sweet corn hybrids (Rogers 'Empire' Bt and non-Bt, respectively) were compared for distribution of kernel damaging insect pests in central Illinois in 1998 and 1999. The occurrence and damage by caterpillars [primarily Helicoverpa zea (Boddie)] were reduced by at least 80% in each year for the Bt compared with the non-Bt hybrid. However, the incidence of sap beetle adults (primarily Carpophilus lugubris Murray) was higher, and larvae, lower for the Bt versus non-Bt in 1999. The incidence of ears with more than five kernels damaged by sap beetles was higher for the Bt compared with non-Bt hybrid in 1998 (13.8 versus 5.5%), but nearly equivalent in 1999 (15.3 versus 15.1%, respectively). Distribution of predators on plants (primarily Coccinelidae) and harvested ears (primarily Orius spp.) were not significantly different on Bt versus non-Bt hybrids. Ears with husks flush with the ear tip or with ear tips exposed had significantly higher sap beetle damage for both hybrids, and the Bt hybrids had significantly higher incidence of exposed ear tips in both years. Sap beetle numbers determined by scouting were often proportional to numbers of beetles captured in baited traps, increasing and decreasing at about the same time. However, values determined with traps were typically less variable than when scouted, and time of sampling was typically four times more rapid for each trap than for each 10 plant scout sample when measured in 1999.