Inhibitory regulation of corpus allatum activity in mosquitoes

In order to determine whether juvenile hormone (JH) in mosquitoes is regulated by ovarian inhibitory feedback, we implanted JH-sensitive pupal ovaries into adult mosquitoes and observed subsequent ovarian maturation. Removal or destruction of resting-stage ovaries (previously JH-stimulated) resulted in JH-stimulated development of implanted pupal ovaries. Ablation experiments demonstrated the ovary-corpus allatum sequence of maturation, and application of exogenous hormone analogs confirmed that development of implanted pupal ovaries is JH-dependent. Incidental observations indicated that ovaries of preapolytic pupae produce a hormone that causes more mature ovaries to degenerate. We concluded that corpus allatum activity in Aedes aegypti is regulated by ovarian feedback inhibition.     

Feeding patterns revealed host partitioning in a community of frog-biting mosquitoes

1. Resource partitioning is a critical component in competing species that coexist in a community. The biting behaviour of coexisting frog-biting mosquito species associated with a tropical anuran community is investigated. 2. Monthly samplings were taken for 2 years at two study sites in central Sri Lanka to collect frog-biting mosquitoes, anuran abundance, environmental data, and interactions between mosquitoes and anuran hosts. Mosquitoes were collected using mouth-operated aspirators and sound traps broadcasting anuran calls. Mosquitoes were identified using taxonomic keys and DNA barcodes. 3. A total of 1079 frog-biting mosquitoes from four species belonging to two genera were collected [Uranotaenia rutherfordi (5%), Ur. morphotype 1 (67%), Ur. morphotype 2 (21%), and Mansonia uniformis (7%)]. Species-specific interactions between Uranotaenia mosquitoes and their anuran host were found. Uranotaenia morphotype 1, the most common species, was mainly attracted (99%) to Duttaphrynus melanostictus. Uranotaenia rutherfordi was mainly attracted (95%) to Pseudophilautus rus, while Ur. morphotype 2 was attracted (97%) to Polypedates cruciger. These Uranotaenia species are active at different hours at night that correspond to the peak calling activity of their anuran host. Each Uranotaenia species was active at heights that coincide with the calling sites of their host. In contrast, Ma. uniformis was non-specific in host choice and was equally distributed in space and time with respect to host feeding. 4. Here, previously unknown feeding patterns of co-occurring frog-biting mosquito species and their interactions with anurans present in their community are reported, highlighting the existence of complex behavioural patterns of these mosquito communities.     

Comparative larvicidal toxicities of three ecdysone agonists on the mosquitoes Aedes aegypti, Culex quinquefasciatus, and Anopheles gambiae

Ecdysone agonists are hormonally active insect growth regulators that disrupt development of pest insects and have potential for development as insecticides. Their effects have been particularly well-studied in Lepidoptera and Coleoptera, but significantly less is known about their effects on dipterans, particularly aquatic species. The potency of three ecdysone agonists on larvae of 3 mosquito species, Aedes aegypti, Anopheles gambiae, and Culex quinquefasciatus, was examined. Anopheles gambiae was the most susceptible species and Ae. aegypti was the most resistant species to the effects of the three compounds tested. Potency, in descending order, was RH-2485 > RH-5992 > RH-5849. Dose-response relationships were determined for the three agonists; RH-2485 was found to be the most effective endocrine disruptor against all three species. The observed biological effects of these compounds were similar to those reported for other insects, and mosquitoes initiated molting and apolysis but did not complete a molt. In some cases, mosquito larvae synthesized a new cuticle that appeared to be normally sclerotized but the larvae failed to ecdyse and shed the exuvium. These compounds may prove to be valuable insect growth regulators for control of mosquitoes to decrease the frequency of pathogen transmission to humans. Prospects for using these compounds to control mosquitoes in the field are discussed, along with possible impacts on non-target arthropods in mosquito habitats.     

Direct PCR of indigenous and invasive mosquito species: a time‐ and cost‐effective technique of mosquito barcoding

Millions of people die each year as a result of pathogens transmitted by mosquitoes. However, the morphological identification of mosquito species can be difficult even for experts. The identification of morphologically indistinguishable species, such as members of the Anopheles maculipennis complex (Diptera: Culicidae), and possible hybrids, such as Culex pipiens pipiens/Culex pipiens molestus (Diptera: Culicidae), presents a major problem. In addition, the detection and discrimination of newly introduced species can be challenging, particularly to researchers without previous experience. Because of their medical importance, the clear identification of all relevant mosquito species is essential. Using the direct polymerase chain reaction (PCR) method described here, DNA amplification without prior DNA extraction is possible and thus species identification after sequencing can be achieved. Different amounts of tissue (leg, head; larvae or adult) as well as different storage conditions (dry, ethanol, ?20 and ?80 °C) and storage times were successfully applied and showed positive results after amplification and gel electrophoresis. Overall, 28 different indigenous and non‐indigenous mosquito species were analysed using a gene fragment of the COX1 gene for species differentiation and identification by sequencing this 658‐bp fragment. Compared with standard PCR, this method is time‐ and cost‐effective and could thus improve existing surveillance and control programmes.     

Multiple blood meals in Anopheles darlingi (Diptera: Culicidae)

Anopheles darlingi is an important vector of human malaria in the Amazon. Adult females of this mosquito species require a blood meal to develop eggs, preferring humans to other blood sources. Although gonotrophic concordance has been described as the norm for An. darlingi, here we report An. darlingi female mosquitoes taking two or more blood meals within their first gonotrophic cycle. Only half of field‐captured adult females fed one blood meal developed follicles to Christophers' stage V. This outcome is dependent on larval nutrition, as 88% of laboratory‐raised well‐nourished females completed the first gonotrophic cycle with only one blood meal, while less nourished females needed additional blood meals. Half of the field‐captured blood‐seeking An. darlingi females had follicles in intermediate (IIIa and IIIb) and final (V) stages of the gonotrophic cycle, supporting the conclusion that An. darlingi blood feed more than once during a gonotrophic cycle. Additionally, we observed females attempting to blood feed a second time during the same day. Additional studies of An. darlingi biting behavior are necessary to accurately estimate Plasmodium sp. entomologic inoculation rates throughout the An. darlingi vast geographical distribution.     

Temporal variation of flower scent in Silene otites (Caryophyllaceae): a species with a mixed pollination system

Floral scent composition and emission are often related to olfactory abilities, preferences and activity times of pollinating agents. However, most studies have focused on species with one pollinator type, and little is known about species with mixed pollination systems. We investigated the temporal variation in flower visitor activity and flower scent emission of Silene otites (Caryophyllaceae), a species regarded as being nocturnal and pollinated by moths and mosquitoes. We found, however, that S. otites is not only visited at night by moths and mosquitoes, but also by a wide range of day‐active insects. Furthermore, both the intensity and composition of floral scent change during the course of the day. Total scent emission reached its maximum in the early hours of the night when compounds known to be attractants for moths and/or mosquitoes, such as lilac aldehyde, benzaldehyde, phenylacetaldehyde and 2‐phenylethanol, dominated the scent. However, although less intensive, emission continued during the day. In the early morning, α‐pinene, hotrienol, 2‐phenylethanol and δ‐3‐carene were the dominant scent compounds. (E)‐β‐Ocimene, hotrienol and benzyl alcohol contributed proportions of at least 10% before midday when flies, such as syrphids, were abundant flower visitors, whereas linalool and hotrienol contributed to the scent with at least 10% each in the afternoon when bees also contributed to flower visits. We conclude that, in S. otites, the changing emission patterns are ‘in tune’ with the olfactory abilities, preferences and activity times of its day‐ and night‐active potentially pollinating flower visitors. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 169 , 447–460.     

Mosquito female response to the presence of larvivorous fish does not match threat to larvae

1. Several species with complex life‐history traits such as amphibians and insects with aquatic immature stages and terrestrial adults avoid ovipositing in pools containing larvivorous fish. This avoidance response was assumed to be a general one for most fish species. 2. The generality of ovipositing Culex to the presence of three, widespread larvivorous fish species was tested in a set of field experiments with artificial oviposition pools using caged fish. 3. Larval performance was further examined under actual predation by these three fish species. 4. Results show that ovipositing females responded strongly to the presence of caged mosquitofish, Gambusia affinis, while showing no significant response to the presence of caged green sunfish, Lepomis cyanellus, or the pirate perch, Aphredoderus sayanus. All three fish species consumed similar amounts of larvae. 5. This is the first example of species‐specific response differences to predators during mosquito oviposition habitat selection. These results point to the existence of predator‐released kairomones affecting mosquito behaviour. These kairomones may either be species‐specific or vary in concentration among fish, and probably have an important role in the understanding of mosquito spatial distribution.