Linking Oviposition Site Choice to Offspring Fitness in Aedes aegypti: Consequences for Targeted Larval Control of Dengue Vectors

Controlling the mosquito Aedes aegypti, the predominant dengue vector, requires understanding the ecological and behavioral factors that influence population abundance. Females of several mosquito species are able to identify high-quality egg-laying sites, resulting in enhanced offspring development and survival, and ultimately promoting population growth. Here, the authors investigated egg-laying decisions of Ae. aegypti. Paradoxically, they found that larval survival and development were poorest in the containers females most often selected for egg deposition. Thus, egg-laying decisions may contribute to crowding of larvae and play a role in regulating mosquito populations. The authors also tested whether removal of the containers producing the most adult mosquitoes, a World Health Organization-recommended dengue prevention strategy, changes the pattern of how females allocate their eggs. Elimination of the most productive containers led to a more even distribution of eggs in one trial, but not another. These results suggest that behavioral adjustments by egg-laying females may lessen the effectiveness of a common mosquito control tactic. The authors advocate incorporating control strategies that take advantage of the natural egg-laying preferences of this vector species, such as luring egg-laying females to traps or places where their eggs will accumulate, but not develop

Oviposition Site Selection by the Dengue Vector Aedes aegypti and Its Implications for Dengue Control

Controlling the mosquito Aedes aegypti is of public health importance because, at present, it is the only means to stop dengue virus transmission. Implementing successful mosquito control programs requires understanding what factors regulate population abundance, as well as anticipating how mosquitoes may adapt to control measures. In some species of mosquitoes, females choose egg-laying sites to improve the survival and growth of their offspring, a behavior that ultimately influences population distribution and abundance. In the current study, we tested whether Ae. aegypti actively choose the containers in which they lay their eggs and determined what cues are most relevant to that process. We also explored whether females select containers that provide the most food for their larval progeny. Surprisingly, egg-laying females were most attracted to sites containing other immature Ae. aegypti, rather than to sites containing the most food. We propose that this behavior may contribute to density-dependent competition for food among larvae and play a larger role than previously thought in regulating Ae. aegypti populations. We recommend that accounting for, and even taking advantage of, this natural behavior will lead to more effective strategies for dengue prevention

Factors Affecting the Distribution and Abundance of an Unpigmented Heterotrophic Alga Prototheca-Richardsi

1. Numbers of the contramensal alga Prototheca richardsi were high in spring in two ponds used for breeding by anuran amphibians, but lower at other times of year and undetectable in two ponds not used by anurans. 2. Prototheca richardsi became abundant in the silt of eight experimental ponds which contained tadpoles, but remained undectable in four otherwise identical ponds lacking tadpoles. 3. Prototheca richardsi numbers in laboratory microcosms remained stable for many days in sterile tap water, but declined with a half-life of about 6 days in pond water at 20-degrees-C. 4. Further studies with microcosms using antibiotics and electron microscopy indicated that mortality of P. richardsi was caused primarily by pathogenic bacteria

Lethal and Sublethal Effects of UV-B/pH Synergism on Common Frog Embryos

Although the negative effects of ultraviolet-B ( UV-B) radiation on the development of many amphibian species have been demonstrated, some speciessuch as the common frog ( Rana temporaria)seem to be tolerant of UV-B radiation. The amount of UV-B radiation received is likely to vary among populations of the same species, but little is known about geographic variation in UV-B tolerance. Similarly, although UV-B radiation can have synergistic effects with other stressors, no studies have focused on geographic variation of these effects on amphibians. We investigated the synergistic effects of UV-B radiation and low pH on hatchability and early development of R. temporaria embryos in a factorial laboratory experiment with animals originating from southern and northern Sweden. Newly fertilized eggs were exposed to three different UV-B treatments (no UV-B [control, 1.254 k/J/m 2[normal and 1.584 k/J/m 2[26 enhanced) and two pH treatments (4.5 [low and 7.6 [neutral). Ultraviolet-B radiation in combination with low pH lead to markedly (approximately 50) reduced survival rates and increased (approximately 30) frequency of developmental anomalies in the northern but not in the southern population. The UV-B- exposed embryos hatched at smaller size in the southern population, whereas low pH reduced hatchling size in both populations. In both populations and pH treatments, embryos in the normal UV-B treatment developed significantly faster than embryos in the enhanced or control UV-B treatments. No interaction between pH and UV-B on developmental rates or hatchling size was detected. The results demonstratecontrary to earlier beliefthat R. temporaria embryos are not insensitive to increased levels of UV-B radiation. The lethal effects of UV-B radiation may, however, become manifested only in combination with other stressors, such as low pH, and the effects of this synergism may differ among different populations of the same species