Ovarian Dynamics in Heliconiine Butterflies: Programmed Senescence versus Eternal Youth

The effect of adult feeding on the fecundity, weight loss and survival of the pine beauty moth, Panolis flammea (D&S)

Adult females of the pine beauty moth, Panolis flammea, fed on a saturated honey solution, laid significantly more eggs than those individuals given water only or not fed at all.At 20°, the longevity of both male and female moths was significantly increased when they were supplied with a food source. At 10° fed male months were not significantly longer lived than unfed moths. Fed female moths at 10° were however, significantly longer lived than unfed individuals. At 20°, fed male moths lived longer than fed females (8.17 days as compared with 5.95 days). At 10°, fed female moths lived longer than fed males (16.00 days compared with 11.41 days).At 20°, weight loss in unfed females over the reproductive period was proportional to the number of eggs laid and the survival time of the individual. In fed females, no significant weight loss occurred over the reproductive period, irrespective of the number of eggs laid or the longevity of the individual.Egg production, even in fed females, over the life span of an individual was only a fifth of the total eggs present in the reproductive tract at eclosion.It is concluded that adult females of P. flammea are likely to require an extra external food source to achieve their full reproductive potential.

Theory of oviposition strategy of parasitoids. I. Effect of mortality and limited egg number

The optimal oviposition strategies of parasitoids, the host range, and the number of eggs laid per host which result in the maximum lifetime performance of reproduction, are investigated. To study the effects of parasitoid mortality and of limiting total number of eggs laid by a parasitoid, a standard criterion used in previous theories of optimal diet and optimal patch use, the maximization of the foraging rate, is no longer suitable. The model is solved analytically by using dynamic programming. The results are as follows: The host preference of solitary parasitoids depends on the mortality during handling times; i.e., the forager tends to avoid hosts with high risk of foraging mortality. If the total number of eggs produced by a parasitoid is limited, and if the mortality during handling is negligible, the host range is wider when a larger number of eggs remains in the parasitoid's body. In general, however, the mortality-cost of forager and the egg-cost interplay, because the loss of future reproduction by mortality increases with the number of available eggs. In an example with two host types, host range is widest with an intermediate number of eggs available in the body. The optimal number of eggs per host laid by a gregarious parasitoid is also affected by the differential mortality of the forager, and by the number of available eggs.

Optimal sugar concentrations of floral nectars -dependence on sugar intake efficiency and foraging costs

A model is developed to elucidate the determinants of sugar concentrations in flower nectars. This model analyses the efficiency of sugar intake, or energy flux, which for nectarivores closely approximates the rate of net energy gain. For both steady state and some non-steady flows of nectars, this energy flux is shown to be maximal at particular sugar concentrations referred to here as the maximum flux concentration. Higher concentrations actually yield lower energy intake rates because the concomitant rapid increase in viscosity sharply reduces the rate of fluid intake. For pure sucrose solutions, the maximum flux concentration is 22%. For flower nectars, which are chemically more complex, the maximum flux concentration is predicted to be closer to 26%, using the first viscosity measures obtained for flower nectars. This concentration is shown to be essentially independent of the pollinator's feeding organ morphology and of the type of potential inducing nectar flow. It is proposed that this concentration applies for virtually all pollinators that select nectars with maximal energy flux.However not all pollinators are expected to select such nectars because this 26% concentration is not necessarily "optimal". The model predicts that optimal sugar concentrations vary for particular pollinators as a function of two primary factors: (1) the energy flux derived from the nectar, as discussed above, as well as (2) the relative contribution of transit costs to overall foraging costs. Relatively "dilute" nectars, with sugar concentrations close to the maximal flux value, are predicted for flowers pollinated by organisms that minimize feeding time to reduce high feeding costs, such as that of hovering or of exposure to enhanced predation while feeding. More concentrated nectars are predicted for flowers pollinated by nectarivores that incur high foraging transit costs relative to feeding costs.Flowers pollinated by hovering pollinators, including many hummingbirds, hawkmoths and bats, have nectars with mean sugar concentrations in close accord with the 26% maximum flux concentration predicted. Moreover, these nectars have relatively low concentrations of nonsugar constituents, which increase viscosity and thereby decrease sugar flux. Over 75% of the flowers examined in this study, which are pollinated primarily by territorial hummingbird species, provide nectars that allow sugar uptake with an efficiency of 90% or greater of the maximal value. According to the model, these data suggest that feeding costs of these pollinators far outweigh foraging transit costs. In contrast, the model suggests that flower nectars taken by traplining hummingbirds and by bees, with sugar concentrations significantly above the maximum flux value, reflect the higher costs of foraging flight relative to costs of feeding for these pollinators.Increasing temperature decreases nectar viscosity, and thereby increases absolute nectar uptake rates sharply. This leads to a number of predictions regarding foraging behavior as well as flower location, orientation, and color. However, the maximum flux concentration is shown to be practically invariable over a wide range of temperatures-increasing by only 2% sugar from 10°C to 30°C. Thus, contrary to previous expectations, little change in average sugar concentrations of flowers pollinated by particular groups of nectarivores is expected from cooler to warmer regions.

Patterns of pollen exploitation by Heliconius butterflies

We have studied pollen feeding habits of ten species of Heliconius butterflies in six major study areas in Trinidad and Costa Rica, and examined inter-species differences in pollen utilization under greenhouse conditions. We found: 1. Females collected significantly more pollen than males. 2. Older individuals generally collected significantly more pollen than younger individuals. 3. Amount of pollen collected may vary significantly through time at a single site, apparently because of changing weather conditions. 4. Amount of pollen collected may vary significantly between species at a single site at a given time, apparently because of differences in per capita resource availability to species using different habitats. 5. Different species had significantly differing abilities to exploit small grained or large grained pollens, which resulted in significant differences in mean pollen collected at different sites by the same species. 6. Species exploiting both large and small grained pollens showed significant differences through time in the ratio of large to small grained pollens utilized.

Specialization: Species Property or Local Phenomenon?

Many herbivorous insects have generalized diets over the species' entire geographical ranges but they function as specialists with restricted diets in local communities. Local feeding specialization can be produced by biochemical, behavioral, ecological, and evolutionary processes. Much evidence is incompatible with the widely held assumptions that diet breadth is a species characteristic and that specialization among herbivorous insects implies greater efficiency and less niche overlap.

Male Contribution to Egg Production in Butterflies: Evidence for Transfer of Nutrients at Mating

Radiotracer studies on three butterfly species showed that nutrients contributed by males through mating are used by females for egg production and possibly for somatic maintenance.