The continuous utilisation of an alternative host may influence parasitoid performance across successive generations due to conditioning in natal hosts. Tetrastichus howardi (Olliff) has successfully been reared using Tenebrio molitor L. pupae as a feasible alternative host. However, the extended rearing of T. howardi on this alternative host may impact the biological features of the parasitoids. Parasitoids were reared using T. molitor pupae for 30 consecutive generations. Quality criteria were assessed during the generations F5, F15, and F30, offering pupae of the target pest, Diatraea saccharalis (Fabr.), and compared with the F0 generation (parasitoids reared in D. saccharalis pupae). Criteria included assessments of parasitism performance, host selection, and wing form variation in the parasitoid wasps. Additionally, we examined the fecundity of T. howardi females that emerged from both hosts, considering their age, egg loading before and after one oviposition, as well as parasitism of sugarcane stalk borer pupae. Rearing T. howardi using pupae of T. molitor did not affect its biological traits or preference for the target pest for 30 generations. After parasitism, the parasitoid left the host pupa inside the stalk, and one oviposition was enough to kill D. saccharalis pupae and obtain viable parasitoid progeny. Female sexual maturation and egg loading occurred 72 and 96 h after parasitoid emergence. Egg-loading recovery after parasitism did not happen within 24 h. T. howardi can be reared for up to 30 generations using alternative hosts without compromising its parasitism performance or egg loading.

The effects of johnsongrass [Sorghum halepense (L.) Pers. # SORHA] infestations were determined during a 2-yr study on sugarcane (Saccharum officinarum L. ‘CP-65-357’) yield. Both cane and sugar yields were lower (36 and 31%, respectively) in plots heavily infested with johnsongrass than in weed-free plots. Sugarcane yields were inversely influenced by johnsongrass equivalents (the sum of the values obtained by multiplying the number of clumps by their corresponding importance value for each plot). In 1983, both johnsongrass standing crop and johnsongrass equivalents correlated negatively with cane yield much better than any other factor combinations, while in 1984, the same was true for stalk population. Substantial yield reductions from johnsongrass interference were observed at johnsongrass infestation levels higher than 15 to 35%.

The sugarcane borer, Diatraea saccharalis (F.), is a pest of graminaceous crops in the southern USA, including sugarcane, maize, and rice. This study was conducted to investigate the effect of silicon (Si) soil amendments on performance of sugarcane borer, D. saccharalis, on two rice cultivars, Cocodrie and XL723. There was a significant increase in the Si content of rice plants supplemented with calcium silicate as compared to non-treated plants. Soil Si amendment led to lower relative growth rates (RGRs) and reduced boring success of sugarcane borer larvae. Effects of soil Si amendments on borer success and RGR appeared to be more pronounced in ‘Cocodrie’, the cultivar relatively susceptible to borers, than in the moderately resistant cultivar, XL723. Soil Si amendment may contribute to the management of D. saccharalis through reduced feeding injury and increased exposure to adverse environmental conditions and natural enemies arising from reduced boring success.

A novel F2 screening technique was developed for detecting resistance in sugarcane borer, Diatraea saccharalis (F.), to transgenic Bacillus thuringiensis (Bt)-maize expressing the Cry1Ab insecticidal protein. The F2 screening method involved (i) collecting larvae from maize fields; (ii) establishing two-parent families; (iii) screening F2 neonates for survival on Bt-maize leaf tissues; and (iv) confirming resistance on commercial Bt-maize plants. With the F2 screening method, 213 iso-line families of D. saccharalis were established from field collections in northeast Louisiana, USA and were screened for Bt resistance. One family was confirmed to carry a major Bt resistance allele(s). In a laboratory bioassay, larval mortality of the Bt-resistant D. saccharalis on Bt-maize leaf tissues was significantly lower than that of a Bt-susceptible strain. This Bt-resistant D. saccharalis population is the first corn stalk borer species that has completed larval development on commercial Bt-maize. The F2 screening protocol developed in this study could be modified for detecting Bt resistance alleles in other similar corn stalk borers, such as the European corn borer, Ostrinia nubilalis (Hübner), and the southwestern corn borer, D. grandiosella Dyar.

Transgenic plants expressing Bacillus thuringiensis δ-endotoxins are now being used commercially in several crop species. These toxins have demonstrated good control of temperate (Ostrinia nubilalis) and tropical (Diatraea grandiosella and D. saccharalis) stemborers in maize. Resistance to B. thuringiensis toxins has been reported in over 11 species in both field and laboratory studies, demonstrating the need for resistance management strategies to prolong the efficacy of this valuable pest management tool within an integrated control programme. Resistance involves reduced binding of toxins to midgut epithelial cells and is generally considered to be a recessive trait. Resistance management will require the use of spatial and temporal refugia which may require unique schemes for each pest complex. Information is presented on the mode of action of cry toxins, resistance mechanisms, interaction of transgenic plants and biocontrol agents, and management/deployment strategies for transgenic maize in tropical ecologies.