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A seed mix strategy has been used to provide refuge to susceptible insects for resistance management in planting transgenic maize expressing Bacillus thuringiensis Berliner (Bt) proteins. To determine whether larval movement in a seed mix planting creates favorable conditions for resistant heterozygotes of a target pest, performance of Cry1Ab-susceptible ( SS) and -heterozygous resistant ( RS) populations of the sugarcane borer, Diatraea saccharalis ( Fabricius) ( Lepidoptera: Crambidae), was evaluated in sequential feeding on non-Bt and Cry1Ab (event MON 810) maize plant tissue. For each insect population, nine feeding sequences were employed. SS and RS feeding on non-Bt plants for their entire larval stages survived well and >60% of the adult pairs produced viable eggs, with an average of 269 progeny per female, whereas none of the two populations on Bt maize plants survived to the pupal stage. SS larvae could not develop to adults if the larvae fed on non-Bt plants for ≤15 days and then moved to Bt plants. In contrast, 4.2-29.2% of RS larvae that fed on non-Bt plants for ≥9 days and then moved to Bt plants developed to adults, and 63.6% of pairs of these adults produced viable eggs, with an average of 185 progeny per female. For SS larvae that fed on Bt plants for 1 or 2 days and then moved to non-Bt plants, few larvae developed to adults with varied emergence times, whereas 28.1 and 13.5% RS larvae feeding on Bt plants for 1 and 2 days, respectively, successfully developed to adults; 43.8% of pairs of these adults produced viable eggs, with an average of 220 progeny per female. For the case of the single Bt gene maize plants (event MON 810), the results suggest that RS insects may have advantages in survival and reproduction over SS if RS larvae hatch and feed on Bt plants during the first 1 or 2 days and then move to non-Bt plants. This advantage is less for RS larvae that hatch and feed on non-Bt plants first and then move to Bt plants, unless the larval movement occurs in the later stages (e.g., fourth or fifth instars). [ABSTRACT FROM AUTHOR]

Sesamia nonagrioides Lefèbvre ( Lepidoptera: Noctuidae) is a key pest of maize [ Zea mays L. ( Poaceae)] and a main target of Bt maize in the Mediterranean area. To choose the most suitable non- Bt refuge strategy for preventing or delaying resistance development in this maize borer, we examined its biology and behaviour. No antixenotic effects were found on numbers of eggs and egg batches per plant in choice ( Bt vs. non- Bt plants) and no-choice assays. However, a greater ratio of young larvae dispersed from Bt than from non- Bt plants. In addition, larvae that hatched on Bt plants tended to disperse more than those that hatched on non- Bt plants, particularly during young growth stages. Many adults, especially females, could fly at least up to 400 m, as was found in a dispersal study with rubidium-marked adults. The stimulation of larval dispersal by the Bt trait and the dispersal capacity of adults might compromise the efficacy of seed mixtures as an insecticide resistance management strategy. [ABSTRACT FROM AUTHOR]

The African stem borer, Busseola fusca (Fuller) (Lepidoptera: Noctuidae), is an important pest of maize and sorghum in sub-Saharan Africa. As in many other lepidopteran insects, the ability of B. fusca to recognize and colonize a variety of plants is based on the interaction between its sensory systems and the physical and chemical characteristics of its immediate environment. In this study, we tried to identify the behavioural steps of B. fusca leading to host selection and oviposition. Three Poaceae species commonly cultivated in Kenya for human consumption and animal forage were used in this study: the two most preferred hosts, maize ( Zea mays L.) and sorghum [ Sorghum bicolor (L.) Moench], and one non-preferred host, Napier grass ( Pennisetum purpureum Schumach). Wind tunnel observations revealed that volatiles produced by the different plant species did not appear to strongly influence the general orientation of B. fusca towards the plant, as similar behavioural steps were exhibited by the female moth regardless of the plant species involved. This indicated that the females were not able to recognize their preferred hosts from a distance. After landing, the female typically swept her ovipositor on the plant surface, simultaneously touching it with the tips of her antennae, and then oviposited. This behaviour was more frequently observed on maize and sorghum than on Napier grass, and indicated that both antennal and ovipositor receptors are used by the female moths to evaluate the plant surface before deciding to oviposit. As a result, the females laid more eggs on the two crops than on Napier grass. We conclude therefore that females recognized their preferred hosts only after landing. Tactile and contact-chemoreception stimuli from the plants seemed to play a major role in oviposition decisions of B. fusca. [ABSTRACT FROM AUTHOR]

Using an F1 screen, 352 feral individuals of the sugarcane borer, Diatraea saccharalis (F.) (Lepidoptera: Crambidae), were examined for the presence of Bacillus thuringiensis (Bt)-resistance alleles. These insects represented four geographical populations collected in central and northeastern Louisiana, USA, and one field population from the Gulf Coast area of Texas, USA, during 2006. The F1 screen used various crosses between field-collected insects and a laboratory strain of Cry1Ab-resistant D. saccharalis, including both reciprocal crosses and group mating. F1 neonates of the crosses were screened for Bt resistance on Bt maize leaf tissue. One field-collected individual of D. saccharalis was shown to have a Bt-resistance allele. Based on Bayesian analysis procedures, the Bt-resistance allele frequency in the five populations of D. saccharalis was 0.0028 with a 95% confidence interval of 0.0003–0.0079. The successful identification of a resistance allele in a field collection of insects suggests that the F1 screening technique could be an effective tool for detecting and monitoring rare Bt-resistance alleles in field populations of D. saccharalis. [ABSTRACT FROM AUTHOR]

The sugarcane borer, Diatraea saccharalis (F.) (Lepidoptera: Crambidae), strain (F52-3-R) was developed from F3 survivors of a single-pair mating on commercial Cry1Ab Bacillus thuringiensis (Bt) corn plants in the greenhouse. The susceptibility of a Bt-susceptible and the F52-3-R strain of D. saccharalis to trypsin-activated Cry1Ab toxin was determined in a laboratory bioassay. Neonate-stage larvae were fed a meridic diet incorporating Cry1Ab toxin at a concentration range of 0.0625 to 32 µg g−1. Larval mortality, larval weight, and number of surviving larvae that did not gain significant weight (<0.1 mg per larva) were recorded on the 7th day after inoculation. The F52-3-R strain demonstrated a significant level of resistance to the activated Cry1Ab toxin. Larval mortality of the Bt-susceptible strain increased in response to higher concentrations of Cry1Ab toxin, exceeding 75% at 32 µg g−1, whereas mortality of the F52-3-R strain was below 8% across all Cry1Ab concentrations. Using a measure of practical mortality (larvae either died or gained no weight), the median lethal concentration (LC50) of the F52-3-R strain was 102-fold greater than that of the Bt-susceptible insects. Larval growth of both Bt-susceptible and F52-3-R strains was inhibited on Cry1Ab-treated diet, but the inhibition of the F52-3-R strain was significantly less than that of the Bt-susceptible insects. These results confirm that the survival of the F52-3-R strain on commercial Bt corn plants was related to Cry1Ab protein resistance and suggest that this strain may have considerable value in studying resistance management strategies for Bt corn. [ABSTRACT FROM AUTHOR]

Target pests may become resistant to Bacillus thuringiensis (Bt) toxins produced by trangenic maize ( Zea mays L.). Untreated refuge areas are set aside to conserve high frequencies of susceptibility alleles: a delay in resistance evolution is expected if susceptible individuals from refuges mate randomly with resistant individuals from Bt fields. In principle, refuges can be toxin-free maize or any other plant, provided it hosts sufficiently large pest populations mating randomly with populations from Bt-maize fields. Our aim was to examine the suitability of several cultivated or weedy plants [pepper ( Capsicum frutescens L.), sorghum ( Sorghum spec .), sunflower ( Helianthus annuus L.), cocklebur ( Xanthium spec .), cantaloupe ( Cucumis melo L.), and hop ( Humulus lupulus L.)] as refuges for Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae) and Sesamia nonagrioides Lefebvre (Lepidoptera: Noctuidae), two major maize pests in southern Europe. Larvae of both species were collected on these plants. Their genetic population structure was examined at several allozyme loci. We found little or no evidence for an influence of geographic distance, but detected a significant host-plant effect on the genetic differentiation for both species. Ostrinia nubilalis populations from sunflower, pepper, cocklebur, and sorghum appear to belong to the same genetic entity as populations collected on maize, but to differ from populations on hop. Accordingly, females from pepper and cocklebur produced exclusively the ‘Z’ type sexual pheromone, which, in France, characterizes populations developing on maize. Qualitatively, these plants (except hop) could thus serve as refuges for O. nubilalis; however, they may be of little use quantitatively as they were found much less infested than maize. Sesamia nonagrioides populations on maize and sorghum reached comparable densities, but a slight genetic differentiation was detected between both. The degree of assortative mating between populations feeding on both hosts must therefore be assessed before sorghum can be considered as a suitable refuge for this species. [ABSTRACT FROM AUTHOR]

Corn (Zea maysL.) borers are the primary target ofBacillus thuringiensisBerliner (Bt) transgenic maize. Management of corn borer resistance to Bt requires information on larval and adult dispersal capacities, a feature that is particularly unknown inSesamia nonagrioidesLefèbvre (Lepidoptera: Noctuidae), the most damaging corn borer in Spain. Larval dispersal was studied over a 3 year period by infesting plants with egg masses and dissecting the neighbouring plants 7, 14, and 32 days later to measure larval dispersal at several ages. The number and age of larvae were recorded in the dissected plants. Only mature larvae dispersed in significant numbers; they moved at least to rows adjacent to those containing the infested plant, and down the row five plants. The percentage of larvae that dispersed from the infested plant was density-dependent. Adult dispersal was studied with directional light and pheromone uni-traps over 5 and 3 year periods, respectively. Directional light traps were placed in the margins between Bt and non-Bt maize fields, half oriented towards each of the two kinds of maize field. Pheromone traps were placed in the Bt and non-Bt fields at increasing distances (0–100 m) from the border. The numbers of males and females caught in directional light traps were not different in traps oriented towards Bt or non-Bt fields, but the number of males caught in the third flight in Bt fields was lower than in non-Bt fields. These results suggest that males from adjacent Bt and non-Bt fields mate indiscriminately with females emerging in any of the two kinds of maize fields. However, male movement in the third flight may not be sufficient to randomly distribute males between the two fields. [ABSTRACT FROM AUTHOR]

Studies the component of the female sex pheromone of a Macadamia nut borer Ecdytolopha torticornis in Costa Rica. Identification of female ovipositor extracts by gas chromatography; Presence of electroantennographic active compounds.