Effects of combination of leaf resources on competition in container mosquito larvae.

Resource diversity is critical to fitness in many insect species, and may determine the coexistence of competitive species and the function of ecosystems. Plant material provides the nutritional base for numerous aquatic systems, yet the consequences of diversity of plant material have not been studied in aquatic container systems important for the production of mosquitoes. To address how diversity in leaf detritus affects container-inhabiting mosquitoes, we examined how leaf species affect competition between two container inhabiting mosquito larvae, Aedes aegypti and Aedes albopictus, that co-occur in many parts of the world. We tested the hypotheses that leaf species changes the outcome of intra- and interspecific competition between these mosquito species, and that combinations of leaf species affect competition in a manner not predictable based upon the response to each leaf species alone (i.e. the response to leaf combinations is non-additive). We find support for our first hypothesis that leaf species can affect competition, evidence that, in general, leaf combination alters competitive interactions, and no support that leaf combination impacts interspecific competition differently than intraspecific competition. We conclude that combinations of leaves increase mosquito production non-additively such that combinations of leaves act synergistically, in general, and result in higher total yield of adult mosquitoes in most cases, although certain leaf combinations for A. albopictus are antagonistic. We also conclude that leaf diversity does not have a different effect on interspecific competition between A. aegypti and A. albopictus, relative to intraspecific competition for each mosquito.

Development, reproduction, and within-plant infestation patterns of Aphis craccivora (Homoptera: Aphididae) on alfalfa.

The goal of this research was to describe developmental rates, reproductive rates, and infestation patterns of Aphis craccivora Koch on alfalfa (Medicago sativa L.). All studies were conducted on the susceptible cultivar OK08 using aphids reared from collections made in Oklahoma. To determine thermal requirements for growth of A. craccivora, development from birth to adult was recorded at 7.2, 12.8, 18.3, 23.9, and 29.4 degrees C. The same constant temperature treatments (except for 7.2 degrees C being raised to 8.3 degrees C) were used to assess the influence of temperature on reproductive rates. Within-plant distribution patterns were determined by infesting three stems on each of 24 plants and recording numbers of A. craccivora on leaf blades, petioles, and internodal stems sections at 2-d intervals through 10 d after infestation. Aphid counts were analyzed to determine significant differences among node parts (leaf blades, petioles, and stem sections). The developmental threshold temperature for A. craccivora was calculated to be 7.1 degrees C, and the thermal constant for development from the first instar to reproducing adult was 100 DD ( degrees C). The optimal temperature range for reproduction on alfalfa was 18-24 degrees C, with a mean of 82 nymphs produced per female. From the initial infestation of three apterae per stem, numbers increased to a mean of 510 per stem after 10 d. Plant profiles showed that the greatest numbers of aphids were located in middle and lower portions of the plant canopy. On all sampling dates, the proportion of aphids on internodal stem sections was significantly greater (P < 0.05) than on petioles and leaf blades.