Field tests of corn co-expressing two new delta-endotoxins from Bacillus thuringiensis (Bt) have demonstrated protection from root damage by western corn rootworm (Diabrotica virgifera virgifera LeConte). The level of protection exceeds that provided by chemical insecticides. In the bacterium, these proteins form crystals during the sporulation phase of the growth cycle, are encoded by a single operon, and have molecular masses of 14 kDa and 44 kDa. Corn rootworm larvae fed on corn roots expressing the proteins showed histopathological symptoms in the midgut epithelium.

A new family of insecticidal crystal proteins was discovered by screening sporulated Bacillus thuringiensis cultures for oral activity against western corn rootworm (WCR) larvae. B. thuringiensis isolates PS80JJ1, PS149B1, and PS167H2 have WCR insecticidal activity attributable to parasporal inclusion bodies containing proteins with molecular masses of ca. 14 and 44 kDa. The genes encoding these polypeptides reside in apparent operons, and the 14-kDa protein open reading frame (ORF) precedes the 44-kDa protein ORF. Mutagenesis of either gene in the apparent operons dramatically reduced insecticidal activity of the corresponding recombinant B. thuringiensis strain. Bioassays performed with separately expressed, biochemically purified 14-and 44-kDa polypeptides also demonstrated that both proteins are required for WCR mortality. Sequence comparisons with other known B. thuringiensis insecticidal proteins failed to reveal homology with previously described Cry, Cyt, or Vip proteins. However, there is evidence that the 44-kDa polypeptide and the 41.9-and 51.4-kDa binary dipteran insecticidal proteins from Bacillus sphaericus are evolutionarily related. The 14-and 44-kDa polypeptides from isolates PS80JJ1, PS149B1, and PS167H2 have been designated Cry34Aa1, Cry34Ab1, and Cry34Ac1, respectively, and the 44-kDa polypeptides from these isolates have been designated Cry35Aa1, Cry35Ab1, and Cry35Ac1, respectively.

Survival and body composition of starving gypsy moth larvae initially reared on aspen foliage or artificial diet differeing in nitrogen (N) and carbohydrate concentration were examined under laboratory conditions. Diet nitrogen concentration strongly affected starvation resistance and body composition, but diet carbohydrate content had no effects on these. Within any single diet treatment, greater body mass afforded greater resistance to starvation. However, starving larvae reared on 1.5% N diet survived nearly three days longer than larvae reared on 3.5% N diet. Larvae reared on artificial diet survived longer than larvae reared on aspen. Differences in survival of larvae reared on artificial diet with low and high nitrogen concentrations could not be attributed to variation in respiration rates, but were associated with differences in body composition. Although percentage lipid in larvae was unaffected by diet nitrogen concentration, larvae reared on 1.5% N diet had a higher percentage carbohydrate and lower percentage protein in their bodies prior to starvation than larvae reared on 3.5% N diet. Hence, larger energy reserves of larvae reared on low nitrogen diet may have contributed to their greater starvation resistance. Whereas survival under food stress was lower for larvae reared on high N diets, growth rates and pupal weights were higher, suggesting a tradeoff between rapid growth and survival. Larger body size does not necessarily reflect larger energy reserves, and, in fact, larger body size accured via greater protein accumulation may be at the expense of energy reserves. Large, fast-growing larvae may be more fit when food is abundant, but this advantage may be severely diminished under food stress. The potential ecological and evolutionary implications of a growth/survival tradeoff are discussed.

A study was conducted in western Montana to determine the impact of dtfferent predators on grasshopper populations. By placing grasshoppers of different species, sexes, _ages, and body masses on monofilament tethers in the field, rates of predation could be e~tm?-ated. These rat~s are consistent with other estimates obtained from population studtes m the same environment, but provide a far more detailed assessment of which grasshoppe~s ~r~ most vulnerable to predators and which predators are most important. Immature mdtvtduals are more vulnerable at small body sizes and adults are more vulnerable at large body sizes; this is because the principal predators on immature individuals are arthropods, and on adults, vertebrates. Male grasshoppers were 2-3 times as vulnerable as females. The subfamily Oedopodinae was more vulnerable than the Gomphocerinae or Melanop~inae. Predation rates indicate that predators are only able to impact seriously (reduce hfe expectancy below the suitable abiotic period for existence) the largest Oedo-pod~nae, making pntdation of little consequence for most grasshopper populations in this envuonment.

Physiological changes during insect ontogeny should be manifest in changes in nutrient requirements and food preference. To investigate ontogenetic changes in food preference and digestive physiology, third-through sixth-instar gypsy moth larvae were provided choices among artificial diets differing in protein and lipid concentrations. Control larvae received two identical cubes of diet that were nutritionally complete, each containing a balanced mixture of protein and lipid. A second group of larvae received two different but complementary cubes, one deficient only in protein, the other deficient only in lipid. During early to late instars, preference shifted away from lipid-deficient, high protein cubes toward proteindeficient, high lipid cubes. This is consistent with the need for late-instar larvae to accrue energy reserves and specific fatty acids required during the pupal and non-feeding adult stages. Male larvae ate a higher proportion from the protein-deficient, high-lipid cube than females, possibly the result of greater energy demands by adult males. Female larvae tended to grow faster on deficient, complementary cubes than larvae provided complete cubes, despite poorer food utilization efficiency. These shifts and sex-specific variations in preference for protein and lipid likely reflect changing nutrient demands and fundamental physiological differences. Food preference Ontogeny Protein Nitrogen Lipid Lymantria dispar