Corn Borer Populations Research Articles

Assessment of the 2022 post-market environmental monitoring report on the cultivation of genetically modified maize MON 810 in the EU.

Following a request from the European Commission, the European Food Safety Authority (EFSA) assessed the 2022 post-market environmental monitoring (PMEM) report on the cultivation of Cry1Ab-expressing maize event MON 810. Overall, the 2022 PMEM report provides no evidence of adverse effects of maize MON 810 cultivation. It shows a high level of compliance with refuge requirements by Spanish and Portuguese farmers growing maize MON 810, but uncertainty remains on compliance in areas where the clustered surface of maize MON 810 farms exceeds 5 ha. There are no signs of practical resistance to Cry1Ab in the field in corn borer populations collected in north-eastern Spain in 2022, although a decrease in Cry1Ab susceptibility in Mediterranean corn borer populations from this area cannot be excluded. Information retrieved through farmer questionnaires in Spain and from the scientific literature reveals no unanticipated adverse effects on human and animal health or the environment arising from the cultivation of maize MON 810. Uncertainties remain on whether 'very highly' and 'extremely' sensitive non-target lepidoptera are potentially exposed to harmful amounts of MON 810 pollen. EFSA notes that several recommendations made in the frame of the assessment of previous PMEM reports remain unaddressed and identified additional shortcomings in the 2022 PMEM report that require further consideration by the consent holder in future annual PMEM reports. Particularly, EFSA emphasises the urgent need to increase the sensitivity of the insect resistance monitoring strategy and implement mitigation measures to ensure that the exposure of non-target lepidoptera to maize MON 810 pollen is reduced to levels of no concern.

Assessment of the 2021 post-market environmental monitoring report on the cultivation of genetically modified maize MON 810 in the EU.

Following a request from the European Commission, the European Food Safety Authority (EFSA) assessed the 2021 post-market environmental monitoring (PMEM) report on the cultivation of Cry1Ab-expressing maize event MON 810. Evidence provided in the PMEM report shows that farmers growing maize MON 810 in Spain complied partially with refuge requirements, while full compliance was achieved in Portugal. Cry1Ab susceptibility tests performed on European and Mediterranean corn borer populations collected from north-eastern Spain in 2021 indicated no symptoms of resistance evolution to maize MON 810. However, unexpected damage to maize MON 810 plants was observed in a field trial in the province of Girona (north-eastern Spain), which may point to the presence of resistance alleles in this region. Information retrieved through farmer questionnaires and the scientific literature reveals no unanticipated adverse effects on human and animal health or the environment arising from the cultivation of maize MON 810. Overall, EFSA concludes that the evidence reported in the 2021 PMEM report does not invalidate its previous conclusions on the safety of maize MON 810. The possible presence of Cry1Ab resistance alleles at frequencies leading to damage to maize MON 810 plants in Girona requires twofold actions: (1) increase monitoring efforts in this area; and (2) implement remedial measures to limit the suspected evolution and spread of resistance. As in previous years, EFSA identified shortcomings on resistance monitoring that need revision. In particular, full refuge compliance must be achieved in Spain. Moreover, the sensitivity of the monitoring plan must be increased, which can be achieved by replacing the current susceptibility assays by periodic F2 screens. EFSA also recommends the consent holder to revise the farmer questionnaires to account for the emergence of teosinte as a noxious agricultural weed in maize MON 810-growing areas in Spain.

Assessment of the 2020 post-market environmental monitoring report on the cultivation of genetically modified maize MON 810 in the EU.

Following a request from the European Commission; the European Food Safety Authority (EFSA) assessed the 2020 post‐market environmental monitoring (PMEM) report on the cultivation of Cry1Ab‐expressing maize event MON 810. Like previous years, there was full compliance with refuge requirement in Portugal and partial compliance with refuge requirements by Spanish farmers growing MON 810 varieties. European and Mediterranean corn borer populations collected from north‐eastern Spain during the 2020 maize growing season and tested for Cry1Ab susceptibility show no symptoms of resistance to maize MON 810. The assessment of farmer questionnaires and relevant scientific publications does not indicate any unanticipated adverse effects on human and animal health or the environment arising from the cultivation of maize MON 810. Overall, EFSA concludes that the evidence reported in the 2020 PMEM report does not invalidate previous EFSA evaluations on the safety of maize MON 810. However, as in previous years, EFSA identifies shortcomings on resistance monitoring that need revision in future reports. In particular, the monitoring plan, as implemented in 2020, is not sufficiently sensitive to detect the recommended 3% resistance allele frequency. Consequently, EFSA strongly recommends the consent holder to achieve full compliance with refuge obligations in areas where adoption of maize MON 810 is high and increase the sensitivity of the monitoring plan by performing periodic F2‐screens on corn borer populations from north‐eastern Spain. EFSA recommends revising the farmer questionnaires when new characteristics of the receiving environment emerge which are relevant for the environmental risk assessment of MON 810 such as the emergence of teosinte. EFSA encourages the Competent authorities of concerned EU Member States, the consent holder and environmental networks to engage in a dialogue to develop a framework on how to best identify and report unexpected adverse effects from the cultivation of Bt maize varieties.

Elevated temperature increases reproductive investment in less preferred mates in the invasive European corn borer moth.

Rapidly changing environments may weaken sexual selection and lead to indiscriminate mating by interfering with the reception of mating signals or by increasing the costs associated with mate choice. If temperature alters sexual selection, it may impact population response and adaptation to climate change. Here, we examine how differences in temperature of the mating environment influence reproductive investment in the European corn borer moth (Ostrinia nubilalis). Mate preference in this species is known to be related to pheromone usage, with assortative mating occurring between genetically distinct E and Z strains that differ in the composition of female and male pheromones. We compared egg production within and between corn borer lines derived from four different populations that vary in pheromone composition and other traits. Pairs of adults were placed in a mating environment that matched the pupal environment (ambient temperature) or at elevated temperature (5°C above the pupal environment). At ambient temperature, we found that within‐line pairs produced eggs sooner and produced more egg clusters than between‐line pairs. However, at elevated temperature, between‐line pairs produced the same number of egg clusters as within‐line pairs. These results suggest that elevated temperature increased investment in matings with typically less preferred, between‐line mates. This increased investment could result in changes in gene flow among corn borer populations in warming environments.

Assessment of the 2019 post-market environmental monitoring report on the cultivation of genetically modified maize MON 810 in the EU.

Following a request from the European Commission, the EFSA assessed the 2019 post‐market environmental monitoring (PMEM) report on the cultivation of Cry1Ab‐expressing maize event MON 810. Like previous years, there was full compliance with refuge requirement in Portugal and partial compliance with refuge requirements by Spanish farmers growing MON 810 varieties. European and Mediterranean corn borer populations collected from north‐eastern Spain during the 2019 maize growing season and tested for Cry1Ab susceptibility show no symptoms of resistance to maize MON 810. The assessment of farmer questionnaires and relevant scientific publications does not indicate any unanticipated adverse effects on human and animal health or the environment arising from the cultivation of maize MON 810. Overall, EFSA concludes that the evidence reported in the 2019 PMEM report does not invalidate previous EFSA evaluations on the safety of maize MON 810. However, as in previous years, EFSA identifies shortcomings on resistance monitoring that need revision in future reports. In particular, the monitoring plan, as implemented in 2019, is not sufficiently sensitive to detect the recommended 3% resistance allele frequency. Consequently, EFSA strongly recommends the consent holder to achieve full compliance with refuge obligations in areas where adoption of maize MON 810 is high and increase the sensitivity of the monitoring plan by performing periodic F2 screens on corn borer populations from north‐eastern Spain. EFSA recommends revising the farmer questionnaires when new characteristics of the receiving environment emerge which are relevant for the environmental risk assessment of MON 810 such as the emergence of teosinte. EFSA encourages the Competent authorities of concerned EU Member States, the consent holder and environmental networks to engage in a dialogue to develop a framework on how to best identify and report unexpected adverse effects from the cultivation of Bt maize varieties.

Variation in degree of pollen exclusion for ga1‐s unilateral cross incompatibility in temperate maize breeding populations

AbstractFertilization and kernel development are crucial for breeding and agronomic production of maize (Zea mays L.), which is prone to outcrossing. Because of this tendency, a major issue for organic corn farmers is to maintain genetic purity of their crop. One way to maintain this purity is to use a unilateral cross incompatibility system such as Ga1‐s. However, lack of complete pollen exclusion has been reported in Ga1‐s heterozygotes, complicating introgression of this trait into breeding germplasm. A systematic, quantitative evaluation of pollen exclusion rates in breeding lines would greatly facilitate use of this system. The purpose of this study is to quantitatively evaluate exogenous ga1 pollen exclusion of a diverse set of Ga1‐s/ga1 F1 hybrids representing the stiff stalk and nonstiff stalk heterotic groups, and the Iowa Synthetic Corn Borer population. Differences between genotypes but not heterotic groups were observed when applying exogenous ga1 pollen onto heterozygotes possessing the same Ga1‐s allele, indicating there are epistatic interactions between Ga1‐s and modifier loci in the ga1 parents tested.

Assessment of the 2018 post‐market environmental monitoring report on the cultivation of genetically modified maize MON 810 in the EU

Following a request from the European Commission, the EFSA assessed the 2018 post‐market environmental monitoring (PMEM) report on the cultivation of Cry1Ab‐expressing maize event MON 810. Like previous years, there was partial compliance with refuge requirements by Spanish farmers growing MON 810 varieties. European and Mediterranean corn borer populations collected from north‐eastern Spain during the 2018 maize growing season and tested for Cry1Ab susceptibility show no symptoms of resistance to maize MON 810. The assessment of farmer questionnaires and relevant scientific publications does not indicate any unanticipated adverse effects on human and animal health or the environment arising from the cultivation of maize MON 810. The report does not provide information about the use of existing networks involved in environmental monitoring. Overall, EFSA concludes that the evidence reported in the 2018 PMEM report does not invalidate previous EFSA evaluations on the safety of maize MON 810. However, as in previous years, EFSA identifies shortcomings on resistance monitoring that need revision in future reports. In particular, the monitoring plan, as implemented in 2018, is not sufficiently sensitive to detect the recommended 3% resistance allele frequency. Consequently, EFSA strongly recommends the consent holder to: (1) achieve full compliance with refuge obligations in areas where adoption of maize MON 810 is high; (2) increase the sensitivity of the monitoring plan and address previously mentioned limitations for resistance monitoring; and (3) perform an F2 screen on corn borer populations from north‐eastern Spain. A fit‐for‐purpose farmer alert system may help to detect unexpected adverse effects associated with the cultivation of MON 810 varieties and be an alternative to the current farmer survey system. Moreover, relevant stakeholders should implement a methodological framework to enable making the best use of existing networks involved in environmental monitoring for the general surveillance of genetically modified plants.

Diapause incidence and critical day length of Asian corn borer (Ostrinia furnacalis) populations exhibit a latitudinal cline in both pure and hybrid strains

The Asian corn borer, Ostrinia furnacalis, is a serious pest and is widely distributed in corn-producing regions throughout China. This insect enters facultative diapause as fully grown larvae in response to short day lengths. Here, we evaluate the changes in diapause incidence and critical day length (CDL) by crossing a tropical strain with five subtropical and temperate strains from a 2897-km latitudinal gradient to investigate the latitudinal variations in diapause induction and CDL and their heredity. Photoperiodic responses of diapause induction in the different geographical strains at different temperatures showed that diapause incidence and CDL increased with increasing latitude and decreased with increasing temperature. Similarly, diapause incidence and CDL for the hybrid strains also showed an increase with increasing latitude or decreasing temperature. Conversely, the diapause incidences were significantly lower and the CDLs were significantly shorter in hybrid strains than their parents with high diapause incidence. Furthermore, the males had significantly more influence than the females on the incidence of diapause in subsequent progeny. Diapause incidence and CDL in O. furnacalis are strikingly different among pure strains and hybrid strains. The photoperiodic response controlling diapause is strongly heritable, with diapause being a partial dominant character over nondiapause, with the incidence of diapause mainly determined by the male parent. These results can help us to predict the time course of diapause induction in nature and may provide a genetic means for pest management by providing information on the overwintering capabilities of the hybrids.

Assessment of the 2017 post-market environmental monitoring report on the cultivation of genetically modified maize MON810.

Following a request from the European Commission, EFSA assessed the 2017 post‐market environmental monitoring (PMEM) report on the cultivation of Cry1Ab‐expressing maize event MON 810. Like previous years, partial compliance with refuge requirements is reported for Spain. European and Mediterranean corn borer populations collected from North‐eastern Spain during the 2017 maize growing season and tested for Cry1Ab susceptibility show no symptoms of resistance to maize MON 810. No complaints about unexpected field damage caused by corn borers were received through the farmer complaint system. The assessment of farmer questionnaires and relevant scientific publications does not indicate any unanticipated adverse effects on human and animal health or the environment arising from the cultivation of maize MON 810. No information about the use of existing networks involved in environmental monitoring is provided. Overall, EFSA concludes that the evidence reported in the 2017 PMEM report does not invalidate previous EFSA and GMO Panel evaluations on the safety of maize MON 810. As in previous years, EFSA identifies methodological and reporting shortcomings pertaining to resistance monitoring that need revision in future PMEM reports. In particular, the monitoring plan, as implemented in 2017, is not sufficiently sensitive to detect the recommended 3% resistance allele frequency. Consequently, EFSA strongly recommends the consent holder to: (1) achieve full compliance with refuge requirements in areas where maize MON 810 adoption is high (i.e. North‐eastern Spain); (2) increase the sensitivity of the resistance monitoring plan and address previously mentioned methodological, analytical and/or reporting limitations for resistance monitoring and farmer questionnaires; and (3) perform a F2‐screen on European and Mediterranean corn borer populations from North‐eastern Spain. Moreover, relevant stakeholders should implement a methodological framework to enable making best use of existing networks involved in environmental monitoring for the general surveillance of genetically modified plants.

Effects of different irrigation levels on European corn borer (Ostrinia nubilalis (Hübner)) populations.

In In this study, the effects of different irrigation treatments (I100, I50, I30) on the European corn borer (Ostrinia nubilalis hübner) populations in different corn genotypes (Ada-9510, Samada-07, Ada-523, Kompozit Arifiye) were investigated. As the average, the highest yield (1582.33 kg da-1), low number of live larva + pupa per plant (2.70), tunnel length (7.73 cm) were observed in I100 x ADA-523 interaction while the lowest yield (896.00 kg da-1) was observed in I30 x Kompozit Arifiye interaction. The largest European corn borer population was observed in full irrigation (I100) and the lowest population was observed in excessive water deficit (I30) treatment. The European corn borer preferred the Kompozit Arifiye genotype. It was concluded that the genotypes should be tested under water-stressed and non-water-stressed conditions for resistance to the European corn borer and live larva and tunnel length could be used as a screening parameter.

Non-Randomness of Fluctuations in the European Corn Borer Ostrinia nubilalis (Hbn.) (Lepidoptera, Crambidae) Long-Term Population Dynamics in Krasnodar Territory

The paper presents the results of analysis of long-term (1994–2017) data on the population dynamics of the local bivoltine European corn borer population developing on maize in the east of Krasnodar Territory. The studied factors, namely the season, the generation within a season, and the development stage (eggs, newly hatched and III–V instar larvae, pupae, adults, and egg-laying females), had highly significant effects on population dynamics. The time analysis of normalized deviations of logarithm densities of III–V instar larvae from the mean values using wavelet decomposition revealed significant periodicity in the abundance fluctuations. Thus, our data radically differ from the commonly assumed sporadic nature of the population dynamics of Ostrinia nubilalis. Since the European corn borer has occurred on maize in Krasnodar Territory for at least 100 years, certain biocenotic control mechanisms significantly changing its population dynamics must have appeared during this time.

Prevalence Rates of the Endosymbiotic Bacterium of the Wolbachia Genus in Natural Populations of Ostrinia nubilalis and Ostrinia scapulalis (Lepidoptera: Pyraloidea: Crambidae) in Southwestern Russia

Analysis of the prevalence rates of the endosymbiotic bacterium of the Wolbachia genus in the populations of corn borers of the Ostrinia genus was carried out. Samples of genomic DNA were extracted from field-collected larvae. The PCR analysis for the presence of Wolbachia infection was performed independently using three diagnostic loci: 16SrRNA, gatB, and fbpA. A positive signal for Wolbachia was obtained for 13.5% of the Ostrinia nubilalis larvae (N = 141) and 31.9% of the Ostrinia scapulalis larvae (N = 138). The infection rate ranged from 2.9% (N = 34) to 65.8% (N = 38) in different geographical populations. At the same time, a significantly higher infection rate of O. scapulalis than O. nubilalis was observed in three out of four habitats. It was also found that the Wolbachia infection was more common for O. scapulalis individuals feeding on hemp than for those collected from mugwort.

Annual post-market environmental monitoring report on the cultivation of genetically modified maize MON810 in 2016.

Following a request from the European Commission, EFSA assessed the annual post‐market environmental monitoring (PMEM) report for the 2016 growing season of the Cry1Ab‐expressing maize event MON 810 provided by Monsanto Europe S.A. Partial compliance with refuge requirements was reported in Spain, as observed in previous years. EFSA reiterates the need to achieve full compliance in areas of high maize MON 810 adoption to delay resistance evolution, and therefore advocates increasing the level of compliance in such areas. Resistance monitoring data do not indicate a decrease in susceptibility to the Cry1Ab protein in the field corn borer populations tested in the 2016 season. However, EFSA identified some methodological and reporting limitations pertaining to resistance monitoring that need improvement in future PMEM reports. No complaints related to corn borer infestation of maize MON 810 were received via the farmer alert system during the 2016 cultivation season. EFSA encourages the consent holder to provide more information on this complementary resistance monitoring tool. The data on general surveillance do not indicate any unanticipated adverse effects on human and animal health or the environment arising from the cultivation of maize MON 810. EFSA reiterates its recommendations on the methodology and analysis of farmer questionnaires, and considers that future literature searches on maize MON 810 performed in the context of annual PMEM reports should follow the guidelines given in the 2017 EFSA explanatory note on literature searching. Moreover, EFSA encourages relevant stakeholders to implement a methodological framework that enables the use of existing networks in the broader context of environmental monitoring. EFSA concludes that no new evidence has been reported in the 2016 PMEM report that would invalidate previous EFSA evaluations on the safety of maize MON 810.

Annual post‐market environmental monitoring (PMEM) report on the cultivation of genetically modified maize MON 810 in 2015 from Monsanto Europe S.A.

Following a request from the European Commission, the Panel on Genetically Modified Organisms of the European Food Safety Authority (GMO Panel) assessed the annual post‐market environmental monitoring (PMEM) report for the 2015 growing season of the Cry1Ab‐expressing maize event MON 810 provided by Monsanto Europe S.A. The GMO Panel concludes that the insect resistance monitoring data submitted to EFSA do not indicate a decrease in susceptibility of field Iberian populations of corn borers to the Cry1Ab protein during the 2015 season. However, since the methodology for insect resistance monitoring remained unchanged compared to previous PMEM reports, the GMO Panel reiterates its previous recommendations on resistance monitoring to provide sufficient detection sensitivity. Although the farmer alert system to report complaints about product performance could complement the information obtained from the laboratory bioassays, the GMO Panel is currently not in a position to appraise its usefulness, and therefore encourages the consent holder to provide more information on this complementary resistance monitoring tool. The data on general surveillance (GS) do not indicate any unanticipated adverse effects on human and animal health or the environment arising from the cultivation of maize MON 810. The GMO Panel reiterates its previous recommendations on the analysis of farmer questionnaires, and advises the consent holder to provide more detailed information on the conducting and reporting of the literature search in future annual PMEM reports. Moreover, the GMO Panel encourages relevant parties to continue developing a methodological framework to use existing networks in the broader context of environmental monitoring. The GMO Panel concludes that the case‐specific monitoring (CSM) and GS activities of maize MON 810 as carried out by the consent holder do not provide evidence that would invalidate previous GMO Panel evaluations on the safety of maize MON 810.

Genetic polymorphism of natural isolates of Nosema Pyrausta (Microsporidia: Nosematidae)

Background. Microsporidia are ubiquitous parasites of animals, most abundant in arthropods and fishes. Many species of these parasites are important from standpoints of medicine, veterinary and agriculture. Microsporidium Nosema pyrausta is an important disease agent in corn borer populations causing adverse effect on host fitness. Genotyping of this parasite is necessary for proper species identification and intraspecific polymorphysm studies.
 Materials and Methods. Microsporidia-infected larvae of corn borers of the genus Ostrinia were recovered from Krasnodar Territory in Russia and Gomel Region in Belarus. Small subunit ribosomal RNA (SSU rRNA) was amplified and sequenced directly, while intergenic spacer (IGS) was amplified, cloned and sequenced (1-5 clones per sample) for four isolates of microsporidia. Sequences were aligned and compared using standard bioinformatics tools (Clustal W and BLAST).
 Results. SSU rRNA genotyping showed allocation of all four isolates to N. pyrausta with 100% identity to each other and 99.7% similarity to Nosema bombycis, the type species of the genus Nosema. High levels of IGS sequence variation (61-74%) is observed both between isolates of different species and populations of microsporidia as well as between molecular clones within parasite isolates from individual hosts.
 Conclusion. N. pyrausta is widespread in corn borer populations and its genetic structure is complicated, as in other species of these parasites. Further studies of molecular markers are needed for genetic differentiation of geographic isolates of N. pyrausta.

Prevalence rates of Wolbachia endosymbiotic bacterium in natural populations of Ostrinia Nubilalis and Ostrinia Scapulalis (Lepidoptera: Pyraloidea: Crambidae) in South-Western Russia

Background. Endosymbiotic bacteria of the genus Wolbachia are widespread in arthropods and often cause reproductive abnormalities in lepidopteran insects, including corn borers of the genus Ostrinia. Wolbachia-Ostrinia is a promising model for studies of parasite-host interactions yet parasite prevalence in natural insect host populations remains unknown.
 Materials and Methods. Molecular genetic screening and statistical analysis is applied to evaluate prevalence rates of Wolbachia in sympatric populations of two corn borer species. Individual genomic DNA samples were extracted from last instar larvae collected in nature from different forage plants. For each sample of DNA showing positive signal with insect-specific primers the detection is performed using three diagnostic loci of Wolbachia: 16SrRNA, gatB and fbpA.
 Results. Wolbachia-positive signal is obtained for 13.5% larvae of Ostrinia nubilalis (N = 141) and 31.9% larvae of Ostrinia scapulalis (N = 138). In different localities the Wolbachia prevalence ranged from 2.9% (N = 34) to 65.8% (N = 38). Significantly higher rates of Wolbachia prevalence in insects from mugwort and hemp (O. scapulalis) as compared to those from corn (O. nubilalis) are revealed in three out of four localities.
 Conclusions. Endosymbiotic bacteria of the genus Wolbachia are revealed in natural populations of corn borers for the first time for Eastern Europe. The prevalence rates can be high and this should be taken into consideration when reproductive isolation is examined in population of these hosts as well as establishment of laboratory cultures is performed.

Can the Use of Trichogramma ostriniae (Hymenoptera: Trichogrammatidae) to Control Ostrinia nubilalis (Lepidoptera: Crambidae) Be Economically Sustainable for Processing Sweet Corn?

European corn borer, Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae), is the main pest causing damage to sweet corn in North America. Conventional management with multiple use of insecticides is a common practice for processing sweet corn. In Canada, the use of Trichogramma spp. began in the 1990s, but the adoption of this approach for European corn borer management is still limited to the fresh market of sweet corn. Trichogramma ostriniae (Peng & Chen) has great potential as a biological control agent for large areas such as in processing sweet corn. The objective of this study was to evaluate an economically and environmentally sustainable alternative to insecticides for controlling European corn borer populations in processing sweet corn. During the growing season, the mean number of larvae decreased after insecticide (0.07 ± 0.04) and Trichogramma (1.32 ± 0.59) treatments compared with the control (2.42 ± 0.72). At harvest, damages associated with European corn borer were similar after Trichogramma (1.0 ± 0.7%) and insecticide (1.0 ± 0.6%) treatments, but significantly lower than the control (8.7 ± 3.3%). This study showed that the use of T. ostriniae can significantly decrease the pressure exerted by European corn borer and its damage on corn ears. This outcome is particularly interesting considering that it was achieved with lower doses of Trichogramma, a lower number of releases, and on large crop areas, compared with what is actually done to protect fresh market corn from European corn borer. Under these conditions, the use of Trichogramma is an economically and competitive alternative to insecticide applications.

Transgenic maize hybrids as a tool to control Sesamia cretica Led. compared by conventional method of control on normal hybrids

This study was conducted on Bt and normal maize hybrids during two successive sowing dates, early and late summer plantation. The Sesamia cretica larvae were observed for the first time on first week of April on different commercial maize hybrids. While there was no larva/plant on transgenic maize hybrids, YieldGard and Ageeb-YG, while larvae were found on last week of July by a very little number on maize hybrids for late one. In Early summer planting date showed highly significant differences in reduction percent, between tested compounds and control one, in the pink corn borer population. The bio-residual activity of the NeemAzal-T/S 0.5% on TWC310 was significantly less pronounced, i.e. 75.5%, than other tested ones; the highest percentage of reduction, 86.6%, was achieved by Chlorophan 0.005% on SC2031, followed by NeemAzal-T/S 0.5% on SC2031 83.5% and Chlorophan 0.005% on SC2030 83.4%, respectively. Also the average reduction percentage of S. cretica larvae differed significantly from 69.6%, on NeemAzal-T/S SC2031, to 83.0%, on Chlorophan SC2031, in the late summer planting. The different treatments had positive effects on maize yield in the two planting dates. In the first plantation date, the increased rate of control ranged from 1.04 to 1.24, when NeemAzal-T/S acted on TWC310 and transgenic IYG, respectively. And in the second plantation date, rate of control obtained was 1.06–1.30, when NeemAzal-T/S acted on SC 2031 and transgenic IYG, respectively. The tested compounds played an important role in controlling the pink corn borer insect, S. cretica, and this study suggests that Cry 1Ab-expressing corn hybrids would provide a great value as a component of corn IPM in Egypt.

Estimating the frequency of Cry1F resistance in field populations of the European corn borer (Lepidoptera: Crambidae)

Transgenic corn hybrids that express toxins from Bacillus thuringiensis (Bt) have suppressed European corn borer populations and reduced the pest status of this insect throughout much of the US corn belt. A major assumption of the high-dose/refuge strategy proposed for insect resistance management and Bt corn is that the frequency of resistance alleles is low so that resistant pests surviving exposure to Bt corn will be rare. The frequency of resistance to the Cry1F Bt toxin was estimated using two different screening tools and compared with annual susceptibility monitoring based on diagnostic bioassays and LC50 and EC50 determinations. An F1 screening approach where field-collected individuals were mated to a resistant laboratory strain and progeny were assayed to determine genotype revealed that resistance alleles could be recovered even during the first year of commercially available Cry1F corn (2003). Estimates of frequency from 2003-2005 and 2006-2008 indicated that, although allele frequency was higher than theoretical assumptions (0.0286 and 0.0253 respectively), there was no indication that the frequency was increasing. Similar estimates in 2008 and 2009 using an F2 screening approach confirmed the presence of non-rare resistance alleles (frequency ≈ 0.0093 and 0.0142 for 2008 and 2009, respectively). The results of both screening methods were in general agreement with the observed mortality in diagnostic bioassays and LC50 and EC50 determinations. These results are consistent with previous modeling results, suggesting that the high-dose/refuge strategy that is in place for Bt corn may be effective in delaying resistance evolution even when a relatively high frequency of resistance alleles exists.

The Effects of Nosema pyrausta Infection on European Corn Borer Populations from Five European Countries

Summary. Ostrinia nubilalis populations from Slovakia, Romania, Austria, Serbia and Germany were collected in the autumn when the insects were in the larval stage. These insects were then established as laboratory populations. The number of pupae and adults that developed was always higher in the Nosema pyrausta non-inoculated (uninfected) populations than in the populations treated by the pathogen N. pyrausta (infected). Signifi cant differences were also found among the populations from different countries. Infected females laid signifi cantly fewer eggs compared to uninfected females. The average time for pupal eclosion or adult emergence was not signifi cantly different between the uninfected and infected populations of O. nubilalis. However, it was found that the infected females laid their eggs signifi cantly sooner as compared to the uninfected females (37.383 days compared to 40.089 days). Under the same conditions, populations from colder regions developed faster than those from warmer regions. The place of origin of the population did not signifi cantly infl uence larval weight, larval length or pupal weight. However, larvae infected with N. pyrausta spores had signifi cantly lower weight (average 0.0797 g) than uninfected larvae (0.0901 g). With regard to pupal weight, the difference between the infected and uninfected individuals was not signifi cant. It was confi rmed that N. pyrausta from one European country can infect and infl uence host larvae originating in other countries. Although there have been several statistically signifi cant interactions with regard to the country of origin and N. pyrausta infection, it was not believed that N. pyrausta from one country would have specifi c effects on the mortality, developmental rate and larval or pupal weight of O. nubilalis populations from different countries.