Aedes albopictus in North America: probable introduction in used tires from northern Asia.

North American strains of Aedes albopictus, an Asian mosquito recently introduced into the Western Hemisphere, exhibit photoperiodic sensitivity and cold-hardiness characteristics similar to strains originating from temperate zone Asia. Trade statistics for used tire imports, the most likely mode of introduction, also indicate a north Asian origin. Aedes albopictus, an important vector of dengue and a potential vector of many other arboviral diseases, may therefore have the capability of infesting much of temperate North America.

Effect of Plasmodium falciparum on blood feeding behavior of naturally infected Anopheles mosquitoes in western Kenya.

Feeding behavior was compared between infected and uninfected field-collected groups of Anopheles gambiae sensu lato and An. funestus from western Kenya. A significantly greater percentage (81%) of Plasmodium falciparum-infected An. gambiae s.l. females probed on experimental hosts (hamsters) than did uninfected females (38%). Among those females that initiated probing, there was no effect of infection status on the ability to take a bloodmeal. Plasmodium falciparum-infected An. gambiae s.l. probed more often (mean = 4.0) and for a longer time (mean = 277 sec) than did their uninfected counterparts (mean = 2.4 probes and mean probing time = 214 sec). Results for the small number of An. funestus that fed followed the same trend. Among infected An. gambiae s.l. females, there was no effect of sporozoite density on either the number of probes made or the total probing time. Among uninfected females, there was no difference in feeding behavior between nulliparous and parous females. In laboratory experiments, female age had no effect on blood-feeding behavior. Our findings provide evidence that natural malaria infection modifies the feeding behavior of Anopheles females.

Ookinete rates in Afrotropical anopheline mosquitoes as a measure of human malaria infectiousness.

Anopheles gambiae s.1. and An. funestus were sampled for Plasmodium spp. ookinetes in two P. falciparum-endemic sites in western Kenya. Since the ookinete is a transitional stage of short duration, occurring after fertilization and before oocyst development, only females in the half-gravid and gravid stages of blood digestion were examined. Preparations of homogenized midguts were spotted onto microslides and examined microscopically after staining with Giemsa. Overall, ookinetes were detected in 4.4% of 1,079 anophelines examined over an eight-month period. Anopheles funestus had higher ookinete rates than An. gambiae s.1., and ookinete rates were higher in half-gravid than in gravid An. gambiae s.1. Geometric mean numbers of ookinetes per infected female were less than five for each species at the two sites, and the maximum number observed was only 12. The low frequencies and numbers of ookinetes were sufficient to produce sporozoite rates of 4-18% in the vector populations. The intense transmission of P. falciparum in these two sites is maintained by anthropophilic vectors where only one in 23 blood meals initiates an infection of generally less than five ookinetes. Relationships between human malaria infectiousness and vector infectivity are dependent upon the high efficiency of the developmental transition from the ookinete to the subsequent oocyst and sporozoite stages.

Plasmodium falciparum infection rates in Anopheles gambiae, An. arabiensis, and An. funestus in western Kenya.

Mosquitoes collected monthly for 1 year from human habitations in the Kisumu area of western Kenya were identified by morphological characters as Anopheles gambiae Giles sensu lato (An. gambiae s.l.) or An. funestus. Of the mosquitoes collected, 7,244 (67%) of the An. gambiae s.l. and 8,511 (87%) of the An. funestus were tested by enzyme-linked immunosorbent assay (ELISA) for the presence of Plasmodium falciparum circumsporozoite (CS) protein. ELISA positivity rates were 8.2% for An. gambiae s.l. and 6.1% for An. funestus. Both An. gambiae and An. arabiensis were detected among 432 ELISA-positive and 668 ELISA-negative An. gambiae s.l. identified to species with a ribosomal DNA probe. The species-specific infection rates were calculated to be 9.6% for An. gambiae and 0.4% for An. arabiensis. These results confirm that An. gambiae and An. funestus are the primary malaria vectors in western Kenya and that An. arabiensis is a relatively minor vector.

Differential oviposition by Aedes hendersoni and Aedes triseriatus (Diptera: Culicidae) in response to chemical cues associated with treehole water.

The oviposition behavior of Aedes hendersoni Cockerell and Aedes triseriatus (Say) was examined in the laboratory by offering gravid females oviposition sites containing water from different treehole types and by varying the physical characteristics of oviposition sites. Ae. hendersoni females oviposited more frequently in containers with water from treeholes in which they are found commonly in nature (maple "deep rotholes") than in containers with water from holes in which they are found rarely (beech "pans"). In contrast, Ae. triseriatus eggs were distributed uniformly in containers holding the two types of treehole water. There were no differences between species in response to oviposition container height or orientation of the entrance hole (vertical or horizontal). Females of both species laid nearly all their eggs in containers with horizontal openings, and most were deposited at the higher of two levels. We suggest that the adaptive value of the oviposition behavior of Ae. hendersoni is to maximize fitness by reducing interspecific contact with Ae. triseriatus.

Sensitivity of a ribosomal RNA gene probe for identification of life stages of Anopheles arabiensis and An. gambiae (Diptera: Culicidae) using three storage methods.

Individual larvae, pupae, female adults, and adult body parts of Anopheles arabiensis Patton and An. gambiae Giles were stored for 1 mo either in isopropanol at room temperature, over a desiccant at room temperature, or at -70 degrees C. DNA was extracted, digested with EcoR1 restriction enzyme, subjected to electrophoresis in agarose gel, transferred to filters, then hybridized to a 32P-labeled rDNA probe. There was no difference among storage treatments in the proportion of correctly identified samples. First instars were not identifiable. Pupae and female adults were more likely to be identified than earlier life history stages. Nonetheless, the probe identified greater than 75% of second instars, 94% of third instars, and 74% of fourth instars. There were no differences between the species in the proportion of identifiable samples for any life history stage.

Comparison of two ribosomal DNA-based methods for differentiating members of the Anopheles gambiae complex (Diptera: Culicidae).

Two DNA-based methods, the restriction fragment length polymorphism (RFLP) and polymerase chain reaction (PCR), were used to identify mosquitoes of the Anopheles gambiae Giles complex collected in Kenya. Field-collected specimens of An. gambiae, An. arabiensis Patton, and An. merus Donity were tested. From a sample of 208 mosquitoes, 181 (87%) were identified by the RFLP method and 205 (99%) were identified by the PCR method. There was complete concordance between the two methods with regard to species identification. PCR assays were simpler, faster, and more reliable than RFLP assays.

Plasmodium species identification by ELISA for sporozoites removed from dried dissection slides.

This study tested the feasibility of identifying salavary gland sporozoites to species by Plasmodium falciparum ELISA by drying them on slides or in vials. The glands were dissected from Anopheles gambiae Giles s.l. and An. funestus Giles collected in western Kenya. In 119 gland infections containing a geometric mean of 1,222 sporozoites, a mean of 72.5% of sporozoites were removed in 60 microliters saline from slides at the time of dissection. Each of the 119 samples was divided into three 18 microliters aliquots. Subsamples were stored at -70 degrees C, dried in vials, or dried on a microslide. When tested by Plasmodium falciparum ELISA, positive reactions were observed in 86.6% of frozen samples, 70.6% of samples held dry in vials, and 50.4% of samples held dry on microslides for 1 mo. Of 90 gland infections where coverslips were removed and slides were left to dry for 1 mo before adding blocking buffer, 81.1% were positive for P. falciparum. This was not significantly different from either frozen gland samples (where 85.5% of 392 infections were identified or frozen gland plus corresponding thorax samples where 86.2% of 160 samples were identified). In malaria field studies, where it is not always practical to freeze samples, sporozoites from dissected mosquitoes can be preserved adequately for ELISA identification by simply removing coverslips and drying dissection slides.

The biology of Aedes thibaulti in northern Indiana.

The biology of Aedes thibaulti was studied in a northern Indiana woodlot. There was a single generation in 1984. Adult emergence began in late May and was complete by mid-June. Females were captured into early August. Female daily survivorship was estimated at 0.954, while female population density peaked at over 2100/ha. Precipitin tests on blood-fed females indicated that Ae. thibaulti fed on vertebrates found in the same woodlot, with deer providing 70% of the meals. Adults were also collected in southwestern Michigan, a new state record for this species.

Response of wild Anopheles funestus to repellent-protected volunteers is unaffected by malaria infection of the vector.

A field experiment was conducted to compare the biting behavior of Plasmodium falciparum-infected and uninfected Anopheles on humans using mosquito repellents. Repellent formulations (5% [wt/vol] N,N-diethyl-3-methylbenzamide [deet] or 5% [wt/vol] AI3-37220, a piperidine compound, both in 100% ethanol, or 100% ethanol alone [as a control]) were applied to the lower legs of 3 collectors in each of 4 houses. Collectors caught mosquitoes over 6 collection nights. Mosquitoes were collected into vials after they initiated probing on the leg of a collector. Infected females made up the same proportion of the Anopheles funestus populations biting either repellent-protected or unprotected individuals. We conclude that repellent formulations are equally effective against Plasmodium-infected and uninfected An. funestus.

Predation of aquatic stages of Anopheles gambiae by the Louisiana red swamp crawfish (Procambarus clarkii).

Laboratory experiments lasting 1-3 days were conducted in 10-liter glass aquaria to evaluate the ability of the Louisiana red swamp crawfish (Procambarus clarkii [Decapoda: Cambaridae]) to consume the aquatic forms of mosquitoes. With Anopheles gambiae as the target species, significantly fewer mosquito larvae or pupae survived in the presence of either juvenile or adult crawfish, relative to conditions without crawfish, regardless of whether crawfish had alternative food or not. When alternative food was excluded, juvenile and adult crawfish had a comparable ability to consume mosquito larvae. However, when alternative food was available, adult crawfish consumed significantly fewer mosquito larvae than did juveniles. In the case of pupae, juvenile crawfish consumed significantly more mosquito pupae than did the adults when alternative food was excluded. No significant difference, relative to controls, was found in the proportion of mosquito pupae surviving when adult crawfish had alternative food. Results of the present study show that P. clarkii has the ability to consume the aquatic forms of anopheline mosquitoes and, therefore, may have an impact on populations of pathogen-transmitting mosquitoes in an area of Kenya where the crawfish has become common.

Malaria prevalence and use of self-protection measures against mosquitoes in Suba District, Kenya.

Malaria prevalence and status among other diseases were assessed in Suba District, Kenya, using data from past parasitological surveys and hospital records of clinically-diagnosed cases. A short prospective survey was also carried out to determine the methods people used for self protection against mosquito bites. Malaria was the leading cause of morbidity, constituting 42-48% of all illnesses clinically diagnosed at two health centres over a two-year period. Other common endemic diseases included infections of the upper respiratory and urinary tracts. The highest monthly number of malaria cases were recorded in July of each year. Malaria parasite rates in blood samples from people examined at 14 screening centres ranged from 24.4% to 99% over a distance of about 25 kilometres. The most popular method of self-protection against mosquitoes was mosquito nets followed by mosquito (pyrethrum-based) coils. Other methods included insecticidal sprays and smoke from plants traditionally associated with mosquito repellence.

Molecular diagnostics of economically important Ceratitis fruit fly species (Diptera: Tephritidae) in Africa using PCR and RFLP analyses.

The predominantly Afrotropical fruit fly genus Ceratitis contains many species of agricultural importance. Consequently, quarantine of Ceratitis species is a major concern for governmental regulatory agencies. Although diagnostic keys exist for identification of all described Ceratitis species, these tools are based on adult characters. Flies intercepted at ports of entry are usually immatures, and Ceratitis species cannot be diagnosed based on larval morphology. To facilitate identification of Ceratitis pests at ports of entry, this study explores the utility of DNA-based diagnostic tools for a select group of Ceratitis species and related tephritids, some of which infest agriculturally important crops in Africa. The application of the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method to analyse three mitochondrial genes (12S ribosomal RNA, 16S ribosomal RNA, and NADH-dehydrogenase subunit 6) is sufficient to diagnose 25 species and two species clusters. PCR analysis of the internal transcribed spacer region 1 (ITS-1) is able to distinguish three of the five species left unresolved by mitochondrial DNA analysis.

Winter cold influences the spatial and age distributions of the North American treehole mosquito Anopheles barberi.

We conducted experiments to assess the importance of winter cold and photoperiod as factors affecting the spatial and age distributions of overwintering larvae of the treehole mosquito Anopheles barberi. Larval dormancy in A. barberi was induced by photoperiods with 14.75 h of light or less per 24 h cycle. About 75% of the larvae entering dormancy were in the second instar regardless of photoperiod. Dormant second instar larvae survived freezing at-15° C for 24 h better than dormant third instar larvae. Larvae were more likely to survive freezing at-15° C in water from treeholes in which they were commonly found in nature than in water from treeholes in which they were unlikely to occur. Female oviposition was significantly higher into water from treeholes in which larvae were likely to be found than in either water from treeholes in which larvae were not commonly found or distilled water. These findings suggest that, in the northern part of its range, the distribution of A. barberi and the age structure of overwintering cohorts are influenced by extreme winter cold. The mechanisms responsible for the distribution of larvae and the overwintering age structure are, respectively, female oviposition behavior and larval photoperiodism.

Parasitoids of medfly, Ceratitis capitata, and related tephritids in Kenyan coffee: a predominantly koinobiont assemblage.

Arabica coffee was sampled from two sites in the central highlands of Kenya (Rurima, Ruiru) and one site on the western side of the Rift Valley (Koru). Three species of ceratitidine Tephritidae, Ceratitis capitata (Wiedemann), C. rosa Karsch and Trirhithrum coffeae Bezzi, were reared from sites in the central highlands, and an additional species, C. anonae Graham, was recovered from the western-most site. Ten species of parasitic Hymenoptera were reared from these tephritids. The parasitoid assemblage was dominated by koinobionts. Eight of the species are koinobiont endoparasitoids, but only one idiobiont larval ectoparasitoid was reared, and only one idiobiont pupal endoparasitoid. The effects of sampling bias on determination of parasitoid assemblage size associated with concealed hosts are discussed. The potential for use of these parasitoids in biological control is also discussed. Most of the parasitoid species recovered during this study are capable of developing on C. capitata, while several also attack C. rosa. Both flies are notorious pests of tropical and subtropical fruits.