Nutrient utilization by caterpillars of the generalist beet armyworm, Spodoptera exigua

Abstract.  Beet armyworm, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae), caterpillars are destructive crop pests responsible for considerable annual economic losses. These generalist herbivores are challenged with a diversity of dietary choices that can impact their survival, development and fecundity. In the present study, dietary choices of S. exigua caterpillars, based on the protein to digestible carbohydrate (P : C) ratio of the food, and the impact of nutritionally unbalanced foods on caterpillar performance are assessed. In choice experiments, individual third-instar caterpillars are offered simultaneously a P-biased and a C-biased food until pupation. Caterpillars feed nonrandomly and select a slightly P-biased diet (22P : 20C). In no-choice experiments, second instar caterpillars are reared until pupation on diets ranging in P : C ratio from extremely P- to extremely C-biased. High mortality and delayed development are observed on the C-rich, P-poor diets, highlighting the potential deleterious effects of excess carbohydrates and the importance of protein for growth and development. Diet-dependent differences in pupal weight or pupal lipid reserves are not observed. This contrasts with closely-related Spodoptera species where pupal mass and lipid stores increase on C-rich, P-poor diets. On the extremely P-biased diet, performance is similar to that of individuals reared on the self-selected diet, suggesting that these caterpillars may efficiently be deaminating excess amino acids to generate carbon skeletons, which are shunted into lipid biosynthesis. Spodoptera exigua caterpillars exhibit flexible and efficient pre-ingestive nutrient intake regulation and post-ingestive utilization, allowing these generalist feeders to cope with the heterogeneous diets they may encounter.     

Identifying Movement States From Location Data Using Cluster Analysis

ABSTRACT Animal movement studies regularly use movement states (e.g., slow and fast) derived from remotely sensed locations to make inferences about strategies of resource use. However, the number of movement state categories used is often arbitrary and rarely inferred from the data. Identifying groups with similar movement characteristics is a statistical problem. We present a framework based on k-means clustering and gap statistic for evaluating the number of movement states without making a priori assumptions about the number of clusters. This allowed us to distinguish 4 movement states using turning angle and step length derived from Global Positioning System locations and head movements derived from tip switches in a neck collar of free-ranging elk (Cervus elaphus) in west central Alberta, Canada. Based on movement characteristics and on the linkage between each state and landscape features, we were able to identify inter-patch movements, intra-patch foraging, rest, and inter-patch foraging movements. Linking behavior to environment (e.g., state-dependent habitat use) can inform decisions on landscape management for wildlife.     

Influence of immature queen honeybees (Apis mellifera) on queen rearing and foraging

ABSTRACT. Providing queenless colonies with five queen cells containing larvae or pupae diminished the number of queen cells and queen cell cups subsequently produced, but not as effectively as the provision of a mated laying queen. Immature queens were more effective than the mature queens in stimulating pollen collection, but were less effective in stimulating nectar collection.     

A New rDNA Repeat Unit in Human Giardia

The rDNA repeat unit from a new human Giardia duodenalis strain shows significant differences from the previously reported G. duodenalis rDNA repeat. Twelve base-pair changes occurred in 490 bp of the SSrRNA gene and new restriction enzyme sites occurred in the LSrRNA gene. The overall length of the rRNA genes is the same but the spacer is 76 bp longer than previously reported. A boundary within the spacers of the two different rDNA units divides a region of 50% homology near the LSrRNA gene from a region of 80% homology toward the SSrRNA gene. This boundary region includes two copies of a 78 bp repeat.