Investigation of fathead minnows (Pimephales promelas) as a biological control agent of Culex mosquitoes under laboratory and field conditions

Comparative Efficacy of Pimephales promelas, Fundulus diaphanus, and Gambusia affinis and Influence of Prey Density for Biological Control of Culex pipiens molestus Larvae

Larval survival times and density-dependent feeding behavior were evaluated with the use of 2 species of fish native to the northeastern USA (Pimephales promelas and Fundulus diaphanus), and the potentially invasive Gambusia affinis. Each species was provided 10, 20, 30, 45, and 60 4th-stage larvae of Culex pipiens molestus/fish in the laboratory and digital images were recorded to quantify the number of surviving larvae at various intervals. Daily feeding rates were greatest at the highest larval density. These were 49.69 ± 4.07 larvae for P. promelas, 60 larvae for F. diaphanus, and 36.44 ± 6.6 larvae for G. affinis. Survival analysis was used to compare efficacy of each fish species over time. All fish species consumed larvae at similar rates at lower densities, but significant differences occurred at densities of 30-60 larvae/fish. Survival times of larvae at the highest density were 44 ± 7.9 h for P. promelas, 15 ± 3.4 h for F. diaphanus, and 70.6 ±13 h for G. affinis. In order to evaluate feeding rate as a function of prey density, we compared consumption rates 1.5 h after feeding with the use of a 4-parameter logistic model. Fundulus diaphanus and G. affinis feeding aligned with the 4-parameter model, indicating that initial feeding rates for these species increased with prey density to an upper limit (satiation). Pimephales promelas feeding within 1.5 h did not align with this model, suggesting that early feeding rates for this species are not heavily influenced by prey density.

Assessing the efficacy of fathead minnows (Pimephales promelas) for mosquito control

Mosquitoes function as important vectors for many diseases globally and can have substantial negative economic, environmental, and health impacts. Specifically, West Nile virus (WNv) is a significant and increasing threat to wildlife populations and human health throughout North America. Mosquito control is an important means of controlling the spread of WNv, as the virus is primarily spread between avian and mosquito vectors. This is of particular concern for avian host species such as the Greater sage-grouse (Centrocercus urophasianus), in which WNv negatively impacts fitness parameters. Most mosquito control methods focus on the larval stages. In North America, control efforts are largely limited to larvicides, which require repeated application and have potentially negative ecological impacts. There are multiple potential advantages to using indigenous fish species as an alternative for larval control including lowered environmental impact, decreased costs in terms of time and financial inputs, and the potential for the establishment of self-sustaining fish populations. We tested the efficacy of using fathead minnows (Pimephales promelas) as biological control for mosquito populations in livestock reservoirs of semiarid rangelands. We introduced minnows into 10 treatment reservoirs and monitored an additional 6 non-treated reservoirs as controls over 3 years. Adult mosquitoes of species known to transmit WNv (e.g., Culex tarsalis) were captured at each site and mosquito larvae were also present at all sites. Stable isotope analysis confirmed that introduced fathead minnows were feeding at the mosquito larvae trophic level in all but one treatment pond. Treatment ponds demonstrated suppressed levels of mosquito larva over each season compared to controls with a model-predicted 114% decrease in larva density within treatment ponds. Minnows established self-sustaining populations throughout the study in all reservoirs that maintained sufficient water levels. Minnow survival was not influenced by water quality. Though minnows did not completely eradicate mosquito larvae, minnows are a promising alternative to controlling mosquito larvae density within reservoirs. We caution that careful site selection is critical to avoid potential negative impacts, but suggest the introduction of fathead minnows in reservoirs can dramatically reduce mosquito larva abundance and potentially help mitigate vector-borne disease transmission.

Malaria in penguins - current perceptions

Avian malaria is a mosquito-borne disease caused by protozoans of the genus Plasmodium, and it is considered one of the most important causes of morbidity and mortality in captive penguins, both in zoological gardens and rehabilitation centres. Penguins are known to be highly susceptible to this disease, and outbreaks have been associated with mortality as high as 50-80% of affected captive populations within a few weeks. The disease has also been reported in wild penguin populations, however, its impacts on the health and fitness of penguins in the wild is not clear. This review provides an overview of the aetiology, life cycle and epidemiology of avian malaria, and provides details on the strategies that can be employed for the diagnostic, treatment and prevention of this disease in captive penguins, discussing possible directions for future research.

Oviposition of Culex tarsalis (Diptera: Culicidae) Differs on Water Conditioned by Potential Fish and Insect Predators

The response of egg-laying Culex tarsalis Coquillett (Diptera: Culicidae) to water conditioned by three fish species used for mosquito control and three predatory aquatic insect species was examined in laboratory binary choice experiments. Oviposition by Cx. tarsalis was 72% less on water conditioned with the arroyo chub, Gila orcutti (Eigenmann & Eigenmann) (Cypriniformes: Cyprinidae) relative to control cups containing aged tap water, but no significant difference was found in the numbers of egg rafts laid on water conditioned with the fathead minnow (Pimephales promelas (Rafinesque), Cypriniformes: Cyprinidae) and the control treatment (water aged 24 h). Mosquito oviposition on water conditioned with the predominantly herbivorous/algivorous California Mozambique tilapia hybrid (Oreochromis mossambicus (Peters) × Oreochromis urolepis hornorum L. (Perciformes: Cichlidae)) or predatory insects (nymphs: Sympetrum corruptum (Hagen) (Odonata: Libellulidae); adults: Thermonectus basillaris (Harris) or Cybister fimbriolatus (Say) (Coleoptera: Dytiscidae)) did not differ significantly relative to that onto water aged for 24 h. As compared with water aged 24 h and water conditioned with diving beetles, oviposition by Cx. tarsalis was significantly lower (≥53%) when live predatory diving beetles were present in oviposition cups. Gravid Cx. tarsalis females do not respond equally to putative semiochemicals in water conditioned with the piscine or aquatic insect predators of immature mosquitoes tested here.