Invasive mosquito predators: the distribution of house geckos

House gecko are common predators of dengue vectors that can be found in many houses in the tropics. Several species occur in Thai homes of which the most common species are the Asian house gecko (Hemidactylus frenatus) and the flat-tailed house gecko (H. platyurus). Hemidactylus species can be found in many parts of the world. During the last few centuries global trade has facilitated their spread, and now they have invaded many parts of the world where they are considered invasive species. In these new regions they often have negative  effects on the local herpetofauna through competition and the spread of parasites and diseases.

In context of mosquito control it may be very useful to understand the distribution of these species and the regions to which they can potentially expand their range. Therefore, we collected secondary species occurrence data from various sources and mapped the current and potential range of five of the most common invasive Hemidactylus species. We found that the Asian house gecko is very common outside its native range, especially in Central America and Australia. The Brook’s house gecko is even more commonly found outside its native range and is very likely to even further expand its range in the future. How this will affect ‘natural’ mosquito control remains unclear. Therefore, investigating the role of these invasive species in the control of mosquitoes will be an important aspect of our future work.

Please follow this link, if you would like to read the complete study.

House Geckos feeding on non-insect foods

House geckos play an important role in the food web in which dengue mosquitoes are embedded. We are conducting a survey to get a better understanding of the opportunistic feeding behaviour of house geckos. House geckos are mostly considered insectivorous but sometimes they also feed on other foods. We are particularly interested in invasive geckos species from the genus Hemidactylus but observations of other species are welcome too.

Please fill out this form if you have ever observed a gecko feeding inside a building on a different location than a window or near a light? If you have observed various species or you have observed a single species at multiple locations, then you can fill out the form several times.

The survey consists of four short questions. The first three questions are about the actual observation (where, what, who) and the last question about the location.

survey

The diets of bats – What about mosquitoes?

Bats are voracious insectivores and may potentially play a role in the control of vector mosquitoes. We analyzed the diets of five bat species in central Thailand and found considerable amounts of mosquitoes in the feces of bats from an urban colony of Taphozous longimanus. Previous studies have shown that bats can have a substantial impact on the abundance of mosquitoes (Reiskind and Wund 2009). However, our field data (unpublished) showed also that there was no correlation between bat feeding activity and Aedes mosquito prevalence. A lack of this correlation could possible be explained by the diurnal character of Aedes mosquitoes. Hence, bats may possibly be more important for the control of nocturnal mosquito species such as Anopheles species which can transmit malaria and Culex species which can transmit the West Nile virus.

You can read more about the diets of bats from central Thailand here.

References

Reiskind MH & Wund MA (2009) Experimental assessment of the impacts of northern long-eared bats on ovipositing Culex (Diptera: Culicidae) Mosquitoes. Journal of Medical Entomology, 46: 1037–1044.

Tadpoles: Do they really eat mosquito larvae?

Tadpoles are often considered to be important predators of mosquito larvae. Hence, we experimentally investigated the predation potential of three different frog species that are common in central Thailand. Unlike generally assumed the tadpoles in our study did not feed on mosquito larvae at all. In fact tadpoles of most frog species do not feed on mosquito larvae, only few species do. But this does not mean that tadpoles do not play a role in the control of mosquitoes at all. Some of the species we studied have been shown to feed on mosquito eggs (Bowatte et al. 2013) and tadpoles are also known to compete for food with mosquito larvae (Mokany and Shine 2003). Such negative effects were also observed in central Thailand (unpublished), where we observed a strong negative correlation between tadpole abundance and mosquito larvae presence.

You can find the complete results of our tadpole-mosquito predation experiment here.

References

Bowatte, G., P. Perera, G. Senevirathne, S. Meegaskumbura, and M. Meegaskumbura. 2013. Tadpoles as dengue mosquito (Aedes aegypti) egg predators. Biol. Contr. 67: 469-474.

Mokany, A. and R. Shine. 2003. Competition between tadpoles and mosquito larvae. Oecologia 135: 615–620.

Dragons and damsels; mosquitoes in distress

Aquatic predators can have a profound impact on the abundance of mosquito larvae. Such predators can include fish such as guppies but also aquatic insects such as backswimmers (Notonectidae) and dragonfly naiads (larvae). We conducted several experiments focusing on various aspects of the predatory behaviour of aquatic insects. One group of insects that we looked at were dragonfly and damselfly naiads (Odonata). We assessed predation rates as an effect of mosquito larvae densities, predator densities and predator size.

We found that predator density had a negative effect on the rates at which individual predators consumed mosquito larvae, but with increasing numbers of predators the total amount of mosquito consumed did increase. However, after a certain threshold of predator densities the total number of mosquitoes consumed decreased. As densities increase the naiads likely experienced a higher threat from conspecifics, because they do like to eat each other as well. While hiding for their neighboring naiads the mosquitoes larvae had a better chance of surviving.

Dragonfly and damselfly naiads appear to be effective predators of mosquito larvae. Although naiads occur in different aquatic habitats than Aedes larvae, they do often co-occur in nature with other vector mosquito species such as Anopheles (Malaria) and Culex (West Nile Virus).

You can find more about this study here.

What do geckos like for diner?

One predator of mosquitoes that is often found inside houses in the tropics are the house geckos. House geckos can be found in all colors and sizes and you can see them often feeding on insects that are attracted to lights. During the day they often hide in dark places, where mosquitoes often hide as well. To find out what impact house geckos have on mosquitoes inside these houses it is important to better understand their feeding behavior.

Together with two students from the University of Applied Sciences Van Hall Larenstein we investigated the feeding behavior of two common house geckos in central Thailand: the Asian house gecko (Hemidactylus frenatus) and the flat-tailed house gecko (H. platyurus). We observed house geckos while feeding and counted the attack rate on various prey and estimated the effort for each attack as the total distance walked towards a prey. The results showed that house geckos prefer moths (Lepidoptera) over any other kind of insect. In addition, house gecko invested slightly more energy in attacks on mosquitoes than on insects from different orders. This slight preference for mosquitoes can possibly be explained by the fact that mosquitoes are soft bodied and are easily digested in contrast to for example beetles which have a hard exoskeleton.

Previous experimental studies have also shown that house geckos can feed on very high number of mosquitoes (Canyon and Hii 1997). However, what the effect of house geckos is on the natural control of mosquitoes in and around our houses remains unclear, but we are working hard to figure that out

You can find the results from the complete study here.

References

Canyon, D.V., Hii, J.L.K. (1997): The gecko: an environmentally friendly biological agent for mosquito control. Medical and Veterinary Entomology 11: 319–323.

How the landscape affects aquatic mosquito predators

Various studies have shown that the prevalence of mosquito borne diseases such as malaria and dengue fever is correlated to deforestation and urbanization. Some factors that can explain such a correlation are, for example, changes in micro-climatic conditions that come with such changes in the landscape but also the availability of breeding habitats for mosquitoes. We wondered if effects on the landscape scale would also affect predator prey interactions. Different species may be affected by landscapes in different ways and it is therefore likely that a correlation between such changes and the abundance of vector mosquitoes could result from changes in predator-prey interactions.

Hence, we conducted a field experiment in which we placed water-filled containers in trees along a gradient of forest and urban habitats and monitored the dengue vectors and predators that colonized these containers. We found that aquatic predators more quickly colonized containers in landscapes that contained more green spaces (think of forests but also urban parks). In addition, the distance to large aquatic habitats also had a major effect on the colonization rate of predators. In containers that were colonized with predators the mosquito densities were much lower.

We can conclude that in urban areas mosquitoes prevail due to a decreased colonization rate of predators, which may be another underlaying factor that helps explaining the relationship between deforestation, urbanization and dengue fever.

You can read more about this study here.

Jumping Spiders Feeding on Mosquitoes

Inside homes spiders are common mosquito predators. But how effective are they at controlling mosquitoes? How many mosquitoes can a spider eat per day? These are valid questions if we seriously want to consider spiders as a biological control agent. To shed some light on these question we did a series of experiments using different species of jumping spiders. We investigated the mosquito feeding rate of these species by releasing mosquitoes and spiders within a closed environment. After 24 hours we counted the number of remaining mosquitoes. We found that female jumping spiders feed on more mosquitoes per day than their male counterparts. Of the 3 species we studied Plexippus paykulli had the highest predation rates. Predation rates were strongly dependent on mosquito density, which significantly increases the catching rate. The predation rates that we observed are similar to that found of other common mosquito predators, which leads to the conclusion that jumping spiders have the potential to be valuable biological control agents for mosquitoes.

You can read the complete study here.

Frogs feed on mosquitoes, but what about mosquitoes feeding on frogs?

We all know that frogs feed on insects. Among these insects mosquitoes are some of its prey. Tadpoles on they other hand are more effective, they feed on the mosquito larvae. These Asian Painted Frogs (Kaloula pulchra) are too busy with other things, so some mosquitoes take their chance and feed on them.

frog

Cupp and his colleagues (2006) investigated this matter back in 2003. They were investigating the role of amphibians and reptiles as a reservoir for eastern equine encephalomyelitis (EEE), a mosquito-borne disease that mainly affects horses but can also affect people. They found that the mosquitoes were feeding for approximately 25% on amphibians, but they main source of blood seemed to come from reptiles. They did not proof that amphibians and reptiles are important hosts for the virus, but there are some indications that point that way. mosquito feeding on frog

Reference:
Cupp, E.W., D. Zhang, X. Yue, M.S. Cupp, C. Guyer, T.R. Sprenger and T.R. Unnasch. 2006. Identification of reptilian and amphibian blood meals from mosquitoes in an eastern equine encephalomyelitis virus focus in central Alabama, American Journal of Tropical Medicine and Hygiene. 71(3): 272–276.

Help us stop dengue and save the environment

Fight dengue fever by saving nature; we need your help.

As the environment deteriorates, dengue fever is increasing worldwide – threatening people in some of the world’s poorest communities. You can help fight back by assisting The Cat Drop Foundation. We are currently developing methods to fight dengue fever through environmental management. The environment has a great impact on the prevalence of mosquitoes, which transmit this deadly disease. With your support, our research can improve the environment by affecting predator species, water quality, and pollution – battling the mosquitoes that thrive in poor conditions. Your donation will be used to acquire equipment and support our important field work. Help us develop strategies that can not just save the environment, but reduce the worldwide burden of dengue fever.