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Although rice ( Oryza sativa L. ) lines that express Bacillus thuringiensis ( Bt ) toxins have shown great potential for managing the major Lepidoptera pests of rice in southern China, including Sesamia inferens, their long-term use is dependent on managing resistance development to Bt toxins in pest populations. The maintenance of "natural" refuges, non-Bt expressing plants that are hosts for a target pest, has been proposed as a means to minimize the evolution of resistance to Bt toxins in transgenic plants. In the current study, field surveys and greenhouse experiments were conducted to identify host plants of S. inferens that could serve as "natural" refuges in rice growing areas of southern China. A field survey showed that 34 plant species in four families can be alternative host plants of S. inferens. Based on injury level under field conditions, rice (Oryza sativa L.); water oat (Zizania latifolia Griseb.); corn (Zea mays L.); tidalmarsh flatsedge (Cyperus serotinus Rottb.); and narrowleaved cat-tail (Typha angustifolia Linn. ) were identified as the primary host plant species of S. inferens. Greenhouse experiments further demonstrated that water oat, corn, and narrow-leaved cat-tail could support the survival and development of S. inferens. Interestingly, greenhouse experiments showed that S, inferens preferred to lay eggs on tidalmarsh flatsedge compared with the other three nonrice host species, although no pupae were found in the plants examined in field surveys. Few larvae were found to survive on tidalmarsh flatsedge in greenhouse bioassays, suggesting that tidalmarsh flatsedge could serve as a "dead-end" trap crop for S. inferens, but is not a candidate to serve as natural refuge to maintain susceptible S. inferens. Overall, these results suggest that water-oat, corn, and narrowleaved cat-tail might serve as "natural refuge" for S. inferens in rice planting area of southern China when Bt rice varieties are planted. [ABSTRACT FROM AUTHOR]

The lepidopteran stemborers Busseola fusca (Fuller) (Lepidoptera: Noctuidae), Sesamia calamistis (Hampson) (Lepidoptera: Noctuidae), and Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) are effectively controlled by Bt maize that expresses the CrylAb insecticidal protein. Another noctuid species, the cutworm Agrotis segetum (Denis and Schiffermüller) (Lepidoptera: Noctuidae), which is the most common and injurious pest of maize seedlings in South Africa, is exposed to Bt toxin for a part of its life cycle. The effect of this exposure to Bt maize has not been studied yet. The aims of this study were to determine the effects of Bt maize (events MON81O and Btll) on larval mass, development time, survival, and fecundity of A. segetwn. Laboratory studies were conducted with firstand fourth-instar larvae and moths. Results showed that the effect of CrylAb toxin on the biology of A. segetum larvae and moths were largely insignificant. The effects of the two Bt maize events on the different parameters measured in this study was not similar between the Bt events and their respective iso-hybrids. Compared with larvae that fed on conventional (non-Bt) maize, Bt maize did not affect survival of first-instar larvae. However, mean mass of larvae that fed on Bt maize (Btll) was significantly lower. Feeding on Bt maize did not have a significant effect on development and survival of fourth-instar larvae or moth longevity. It did, however, delay the development period to pupa formation. Fewer eggs were laid by moths fed as larvae on maize event Btll compared with MON81O. This study indicates that Bt maize will most likely not have any significant effect on the control of A. segetum under field conditions. [ABSTRACT FROM AUTHOR]

Genetically modified insect-resistant rice lines containing the crylAc gene from Bacillus thuringiensis (Bt) or the CpTI (cowpea trypsin inhibitor) gene developed for the management of lepidopterous pests are highly resistant to the major target pests, Chilo suppressalis (Walker), Cnaphalocrocis medinalis (Guenée), and Scirpophaga incertulas (Walker), in the main rice-growing areas of China. However, the effects of these transgenic lines on Sesamia infereris (Walker), an important lepidopterous rice pest, are currently unknown. Because different insect species have varying susceptibility to Bt insecticidal proteins that may affect population dynamics, research into the effects of these transgenic rice lines on the population dynamics of S. inferens was conducted in Fuzhou, southern China, in 2005 and 2006. The results of laboratory, field cage, and field plot experiments show that S. inferens has comparatively high susceptibility to the transgenic line during the early growing season, with significant differences observed in larval density and infestation levels between transgenic and control lines. Because of a decrease in CrylAc levels in the plant as it ages, the transgenic line provided only a low potential for population suppression late in the growing season. There is a correlation between the changing expression of CrylAc and the impact of transgenic rice on the population dynamics of S. inferens during the season. These results indicate that S. inferens may become a major pest in fields of prospective commercially released transgenic rice, and more attention should be paid to developing an effective alternative management strategy. [ABSTRACT FROM AUTHOR]

The Mediterranean corn borer, Sesamia nonagrioides (Lefebvre) (Lepidoptera: Noctuidae), is a major pest of maize in the Mediterranean area. Transgenic Bt maize expressing the CrylAb toxin from the bacterium Bacillus thuringiensis can effectively control this pest. The characterization of S. nonagrioides population structure, at a large geographical scale, would provide some insight in decision making for resistance management. The genetic relationships among nine populations from Spain, one from France, one from Italy, three from Greece, and one from Turkey were assessed using Random Amplyfied Polymorphic DNA (RAPD) markers. Populations from France and Spain formed a cluster independent from a cluster of populations collected in Italy, Turkey, and Greece in a unweighted pair-group method with arithmetic average dendrogram constructed from Nei's genetic distances. Average genetic differentiation among samples was significant for all geographical groupings analyzed (FST = 0.160 ± 0.014 for Spanish populations; 0.133 ± 0.022 for Spanish and French populations; and 0.095 ± 0.010 for Greek, Italian, and Turkish populations). Genetic differentiation was also significant for all paired comparisons of populations, including two Spanish populations separated by only 15 km with no apparent geographical barriers. No pattern of isolation by distance was observed among Mediterranean corn borer populations collected in Spain and France. These results suggest a limited genetic exchange between relatively distant S. nonagrioides populations in Europe, which might contribute to decreased rate of spread of resistance alleles once resistance has developed at a certain site. [ABSTRACT FROM AUTHOR]

During the dry season in the humid forest zone of Cameroon, maize is the most important off-season cash crop grown in hydromorphic inland valleys (IVs), which may also be reservoirs for pests such as the stemborer Busseola fusca Fuller and its natural enemies. Pest and parasitoids were monitored in IVs and close-by upland maize fields from January 2002 through December 2004. Trap catches and oviposition data showed that B. fusca was active throughout the dry season and long and short rainy seasons of 2004. Egg batch densities were considerably lower in the dry than in the rainy seasons. Important natural enemies were the scelionid egg parasitoids Telenoinus busseolae Gahan and T. isis Polaszek. B. fusca was the predominant borer species in all seasons in maize in IVs as well as in upland fields, followed by Sesamia calamistis Hampson and Eldana saccharina Walker. B. fusca larval densities were lowest in the IVs and increased in the course of the year in the upland fields. In contrast, S. calansistis densities were higher in IVs than in upland maize fields. At harvest of the IV maize, B. fusca and E. saccharina larval densities were 47.3 and 15.5 times higher, respectively, than on old maize stubbles in upland fields planted during the previous year. Grain yields as well as the marketable ear index were 1.1-2 times higher in the dry season than in the long and short rainy seasons, indicating the importance of IVs for dry season maize production in Cameroon. [ABSTRACT FROM AUTHOR]

Laboratory studies on the temperature-dependent development of Sesamia nonagrioides (Lefebvre) were performed under five constant temperatures ranging from 20 to 30°C as well as under the corresponding alternating temperatures of 25:10, 27.5:12.5, 30:15, 32.5:17.5, and 35:20°C, at a photoperiod of 16:8 (L:D) h. Both linear and nonlinear (Lactin formula) models provided a reliable fit of developmental rates versus temperature for all immature stages either at constant or alternating temperatures. Developmental thresholds that were estimated by a linear model for eggs, larvae, or pupae were approximately the same and estimated to be 10.57, 8.89, and 10.75°C, respectively, at constant temperatures. Lower values were estimated when immature stages were exposed to the corresponding alternating temperatures (7.23, 6.20, and 6.50°C for eggs, larvae, and pupae). Therefore, the evaluation of the development of immature stages under constant temperatures resulted in an overestimation of the lower thresholds. The Lactin-2 model also was applied, and larval and egg developmental thresholds did not differ from those that were estimated by the linear model. Differences, however, occurred at the pupal stage. Nevertheless, the differences in the estimated values of the lower developmental thresholds of the immature stages under constant or alternating temperatures indicate that a model predicting phenology in the field should be based on fluctuating temperature. KEY WORDS Sesamia nonagrioides; developmental rate; constant temperature; alternating temperatures. [ABSTRACT FROM AUTHOR]