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The presence of Ixodes ricinusand their associated Borreliainfections on large grazers was investigated. Carcases of freshly shot red deer, mouflon and wild boar were examined for the presence of any stage of I. ricinus. Questing ticks were collected from locations where red deer and wild boar are known to occur. Presence of Borrelia burgdorferis.l. DNA was examined in a fraction of the collected ticks. Larvae, nymphs and adult ticks were found on the three large grazers. Red deer had the highest tick burden, with many of the nymphs and adult females attached for engorgement. Most larvae had not attached. The mean number of ticks on the animals varied from 13 to 67. Ticks were highly aggregated amongst the animals: some animals had no ticks, while others had high numbers. Larvae and nymphs were mostly found on the ears, while adult ticks were attached to the axillae. The Borreliainfection rate of questing nymphs was 8.5%. Unengorged wandering nymphs on deer had a Borreliainfection rate of 12.5%, while only 0.9% of feeding nymphs carried a Borreliainfection. The infection rate of unengorged adult male ticks was 4.5%, and that of feeding female ticks was 0.7%. The data suggest that ticks feeding on red deer and wild boar lose their Borreliainfections. The implications of the results are discussed with respect to Borreliaepidemiology and maintenance of a Borreliareservoir as well as the role of reproductive hosts for Ixodes ricinus.

Studies on the behavioral and oviposition responses of Culex quinquefasciatusto 3-methylindole or skatole (an oviposition site cue) and (5R,6S)-6-acetoxy-5-hexadecanolide (the synthetic oviposition pheromone, SOP) were conducted in Muheza, northeast Tanzania. Cx. quinquefasciatusdisplayed a bimodal pattern of oviposition. The highest peak (64.8%) was between 18:00 and 20:00 hr, while the second peak (18.9%) was between 06:00 and 08:00 hr. The mean number of egg rafts oviposited per day between the two peaks was different (P< 0.05). Oviposition responses of gravid Cx. quinquefasciatusdiffered across the range of concentrations of skatole. Larger numbers of egg rafts were deposited in bowls treated with 10−6μg or 10−5μg skatole than in bowls with tap water (P< 0.05). The number of egg rafts deposited in bowls treated with 10−4or 10−1μg skatole was not different from that laid in tap water (P> 0.05). Under field conditions skatole was found to be effective for a period of seven days, after which its biological activity decreased significantly. It was further found that more egg rafts of Cx. quinquefasciatuswere deposited in water treated with SOP than in water treated with skatole (P= 0.0002). An additive effect was observed when the SOP + skatole combination was used to attract gravid Cx. quinquefasciatusto oviposition sites. It is concluded that skatole and SOP mediate oviposition site selection of Cx. quinquefasciatusunder field conditions.

The response of Culexmosquitoes to (5R,6S)-6-acetoxy-5-hexadecanolide (the synthetic oviposition pheromone, SOP), emanations from soakage pit water (SPW), and grass infusions (GI) was studied in pit latrines in Muheza, Tanzania. Water treated with the synthetic oviposition pheromone received more egg rafts of Culex quinquefasciatusSay and Cx. cinereusTheobald than did the untreated water (P< 0.001). The residual activity of SOP did not decrease over a nine-day period, with the geometric mean number of egg rafts laid in the SOP-treated water varying daily between 2.5 and 8.9 as compared to 0.1–1.6 egg rafts laid in tap water. However, SOP did not attract ovipositing mosquitoes to nonbreeding sites, and both treatment and control received few eggs. SPW and GI attracted ovipositing Cx. quinquefasciatus, Cx. cinereus, and Cx. tigripesGrandpré and de Charmoy with the number of eggs rafts deposited in bowls containing SPW or GI being larger than that deposited in bowls with tap water (P< 0.05). More egg rafts of Cx. quinquefasciatuswere deposited in SOP-treated water than in SPW (P< 0.05). When SOP was compared with SOP + SPW, more egg rafts of Cx. quinquefasciatuswere deposited in bowls with the latter combination than in bowls containing SOP or SPW only (P< 0.05), indicating a synergistic effect between SOP and SPW. Similarly, when SOP-treated water and GI were compared with SOP + GI, more egg rafts of Cx. quinquefasciatuswere laid in the latter bowl, indicating a synergistic effect between SOP and GI. The result suggest that the combined use of SOP and organically enriched water can be employed in monitoring of Cx. quinquefasciatusfor control programs. This is the first record of the attraction of Cx. cinereusand Cx. tigripesto oviposition stimuli.

Field experiments to determine the host preference of Culex quinquefasciatusSay (Diptera: Culicidae) between man, calf and goat, were conducted in Muheza, north‐east Tanzania. The responses of the mosquito to the three hosts were also compared to their responses to carbon dioxide. A total of 2565 unfed female mosquitoes were collected, of which Cx quinquefasciatusaccounted for 96.6% of the catch. A human‐baited tent caught a larger number of host‐seeking Cx quinquefasciatusthan a calf‐baited or goat‐baited tent (P<0.05). The man:calf ratio was 7.8:1 while the man:goat ratio was 10:1. The difference in response to either a calf‐ or goat‐baited tent was not statistically significant (P>0.05). The number of mosquitoes attracted to a human‐baited tent was significantly larger than that attracted to carbon dioxide released at 300 ml min−1. Only 25.3% of the human host attractancy was attributed to carbon dioxide. The number of Cx quinquefasciatusresponding to a tent baited with a calf or goat was not significantly different from the number responding to a tent baited with carbon dioxide. It can be concluded that with equal availability of the three vertebrate hosts, Cx quinquefasciatuswould respond more to volatile cues from a human host than from either a calf or goat, thereby supporting earlier data about its high degree of anthropophily. The major olfactory cue from a goat or a calf to which this mosquito responds is probably carbon dioxide.

A tsetse survey was conducted around the Lambwe Valley in South West Kenya in order to establish the extent of Glossina pallidipesdistribution outside the Valley. Between October 1988 and March 1989 flies were found far outside the Lambwe Valley. A proportion of these flies was infected with three species of trypanosomes. The capture of teneral flies suggested that breeding was occurring and that viable populations of G. pallidipestherefore exist away from the core breeding areas in the valley. L’etendu de la distribution de Glossina pallidipesau dehors de la vallee de Lambwe, dans le sud-ouest du Kenya, à été etablie par moyen d’une prospection. Entre Octobre 1988 et Mars 1989 des mouches tsetse ont été trouvées a grande distance de la vallée. Une proportion de ces mouches était inféctée de trois espèces de trypanosomes. Il est evident que la mouche se réproduit au dehors de la vallée de Lambwe, et que des populations viables de G. pallidipesexistent loin des noyaux de reproduction dans la vallée.

The flight behavior of Anopheles gambiae s.s. Giles and An. stephensi Patton exposed to different odor cues was studied in a wind tunnel. Odors consisted of CO2, CO2+ acetone (at two concentrations), and CO2+ 1-octen-3-ol. Mosquitoes were released singly and their behavior was recorded on video. Parameters studied included flight velocity, percentage of time spent flying, percentage of time spent in plume, and number of turns toward the plume. Large differences in behavior toward the odors tested were observed. An. gambiaedid not respond well to CO2,whereasAn. stephansiwas positively affected by this compound. In contrast, An. gambiaeresponded significantly to CO2+ acetone (at a low concentration), but the behavior ofAn. stephensiwas completely suppressed by this combination of odor stimuli. CO2+ a high concentration of acetone or CO2+ 1-octen-3-ol did not cause significant effects inAn. gambiaecompared to no odor, while these treatments elicited strong behavioral responses inAn. stephensi.The latter species responded particularly well to CO2+ 1-octen-3-ol. The results suggest that the observed differences may be inherent to the known differences in host preferences, whereAn. gambiaeis highly anthropophilic andAn. stephensimore zoophilic. This would explain why the latter species responds well to CO2and even better to CO2+ 1-octen-3-ol, a compound readily emitted by bovine ruminants.

Biconical traps were studied for their efficiency in sampling for Glossina morsitans morsitansWestw., G. pallidipesAust., G. austeniNewst. and G. brevipalpisNewst. in three localities in Mozambique where these species occur sympatrically or singly. Studies were also carried out to determine whether acetone vapour was effective in enhancing the efficiency of the biconical trap. Various comparisons were also made between biconical traps and Langridge traps, and with fly-round patrols, with and without bait oxen. p ]It was demonstrated initially that the blue biconical trap (BBT) was more efficient for G. morsitansand G. pallidipesthan red or white models or Langridge traps. In all subsequent studies, therefore, the BBT was used. It was concluded that: the BBT was ineffective for sampling G. morsitans, with or without acetone; the BBT was markedly more effective than fly rounds for sampling G. pallidipes, and its efficiency was significantly enhanced by acetone; and G. austeniwas attracted to the BBT, but not all flies would enter the non-return cage—G. brevipalpiswas readily caught in the BBT. Acetone with the BBT gave inconclusive results for these species.

The efficacy of the trypanocides Samorin and Prothidium to protect beef cattle in areas of different trypanosome challenge was studied in Muabsa, Mozambique during an 18 month period. The performance of two groups of 1.5- to 3-year old bulls was observed, the first group in an area of high tsetse density, the second in an area of low to medium tsetse density.Glossina morsitans and G. pallidipes were present and their respective densities were determined using standard fly rounds, a mobile electric screen and biconical traps. The trypanosome challenge was determined using parameters of tsetse density and infection rates; the trypanosome risk was determined by Berenil Indices in both groups of animals.

The experimental application by helicopter of six insecticides to riverine forest galleries of the Komoe River in Upper Volta against Glossina tachinoides Westw. was monitored for its effects upon non-target organisms, in particular birds, fish, insects and crustaceans inhabiting the experimental area. There was no recognisable mortality associated with applications of these insecticides on birds or fish. Aerosol applications of permethrin and decamethrin produced mortalities in two species of crustacea and very high mortalities occurred from a residual treatment of decamethrin at 12.5 g a.i./ha.

The rationale is presented for the development of techniques for applying insecticides by helicopter in small-scale field trials against Glossina tachinoides, an important vector of human sleeping sickness. This approach has been adopted in view of the difficulty of applying non-residual insecticides to the riverine forest habitat by fixed-wing aircraft and the need to test the efficacy of new insecticides to ascertain effective dosages. Six insecticides were tested; endosulfan, decamethrin, permethrin, azamethiphos tetrachlorvinphos and fenthion. The trials were carried out in the River Komoe valley, a typical humid savanna area with savanna woodland, woodland/floodplain ecotones, moist riverine forest and dry forest as the main vegetation types. Glossina tachinoides was the only tsetse fly present in sufficient numbers for it to be used for evaluation in the trials, it feeds on bushbuck and carries Trypanosoma grayi, a parasite of crocodiles and Varanus spp. The area was divided into an untreated control zone, droplet penetration study area and experimental airspray blocks. Prior to the trials themselves it was necessary to undertake equipment tests and droplet size and spray penetration studies in selected typical riverine forest habitats; to determine the most effective method of aerosol application in the riverine forest and to ascertain, through meteorological studies, the most appropriate time of day to apply the pesticide. It was also necessary to monitor the effects of the insecticide applications on the non-target organisms inhabitating or associated with the gallery forest. Detailed reports of these activities are given in accompanying papers.

The effectiveness of CO2-baited and human-baited mosquito traps for the sampling of Anopheles darlingi Root was evaluated and compared with human landing collections in Suriname. Biting preferences of this mosquito on a human host were studied and related to trapping data. Traps used were the Centers for Disease Control and Prevention Miniature Light trap, the BG Sentinel mosquito trap, the Mosquito Magnet Liberty Plus mosquito trap (MM-Plus), and a custom-designed trap. Carbon dioxide and humans protected by a bed net were used as bait in the studies. The number of An. darlingi collected was greater with human landing collections than with all other collection methods. An. darlingi did not show a preference for protected humans over CO2 bait. The BG Sentinel mosquito trap with CO2 or human odor as bait and the MM-Plus proved the best alternative sampling tools for An. darlingi. The BG Sentinel mosquito trap with CO2 or human odor as bait was also very efficient at collecting Culex spp. In a field study on biting preferences of wild An. darlingi, the females showed directional biting behavior (P < 0.001), with a majority of females (93.3%) biting the lower legs and feet when approaching a seated human host. Higher efficiency of the closer-to-the-ground collecting MM-Plus and BG Sentinel mosquito trap when compared with the other trapping methods may be a result of a possible preference of this mosquito species for low-level biting. It is concluded that odor-baited sampling systems can reliably collect An. darlingi, but the odor bait needs to be improved, for instance, by including host-specific volatiles, to match live human baits.

The effectiveness of traps baited with (5R,6S)-6-acetoxy-5-hexadecanolide (the synthetic oviposition pheromone) and grass infusions in sampling a population of gravid Culex quinquefasciatus Say was conducted in Muheza, Northeast Tanzania. A counterflow geometry (CFG) trap baited with pheromone and set outdoors, adjacent to a pit latrine building, collected more gravid Cx. quinquefasciatus than a CDC trap baited with pheromone and operated without light. Inside pit latrine buildings, significantly more gravid Cx. quinquefasciatus were collected in a CFG trap-baited with pheromone or grass infusion than in traps baited with tap water. CFG traps baited with either grass infusion or pheromone and set outdoors, away from known breeding sites, caught significantly more gravid Cx. quinquefasciatus than traps baited with tap water. CFG traps baited with pheromone + grass infusion caught significantly more gravid Cx. quinquefasciatus than CFG traps baited with either grass infusion or pheromone. In both cases, the proportion of gravid mosquitoes increased as traps were moved away from a natural emergence site. More gravid Cx. quinquefasciatus were collected in a pheromone-baited CFG trap than were egg rafts deposited in a jar with pheromone-treated water. It is concluded that CFG traps baited with oviposition attractants can be used effectively to sample gravid Cx. quinquefasciatus.

The survival, metabolic reserves, and host-seeking response of unfed Anopheles gambiae Giles sensu stricto females of different size classes were investigated from 1 to 6 d after emergence. In addition, the effect of blood meal size and frequency of feeding on the accumulation of metabolic reserves and reproductive development were investigated during the 1st gonotrophic cycle. Large females survived longer and contained significantly more protein, glycogen, and lipid at emergence than did small females. Over 6 d, the host-seeking response of large mosquitoes was greater than that of small ones. There was no gonotrophic development in unfed small females after emergence, whereas =52% of large females developed oocytes to Christophers stage II. One blood meal, given by enema, resulted in gonotrophic development to stage II in small females, whereas only large females matured oocytes to Christophers stage V. In both large and small females, egg development was related to the size of the blood meal, but large females were better able to utilize the meals. Two successive blood meals enhanced the ability of small females to develop eggs. The pregravid condition commonly observed in An. gambiae appears to be determined by insufficient metabolic reserves at emergence, and the probability for small individuals to be pregravid is greater than for large mosquitoes because of the need to build up sufficient energy reserves before gonotrophic development can occur. The consequence of this behavior in relation to malaria transmission is discussed.

The current geographic range of malaria is much smaller than its potential range. In many regions there exists a phenomena characterized as“Anophelism without malaria.“ The vectors are present but malaria transmission does not occur. Vectorial capacity often has been used as a parameter to estimate the susceptibility of an area to malaria. Model computations with global climatological data show that a dynamic concept of vectorial capacity can be used as a comparative risk indicator to predict the current extent and distribution of malarious regions in the world. A sensitivity analysis done in 3 distinct geographic areas shows that the areas of largest change of epidemic potential caused by a temperature increase are those where mosquitoes already occur but where development of the parasite is limited by temperature. Computations with the model presented here predict, with different climate scenarios, an increased malaria risk in areas bordering malaria endemic regions and at higher altitudes within malarious regions under a temperature increase of 2–4°C.

Four aspects of olfaction in host location by tsetse flies, Glossina spp., are discussed as follows: (1) host location and its mechanism, (2) factors affecting host location, (3) kairomones and host location, and (4) kairomones and host selection. Flight behavior in the various phases of host location (i.e., ranging, activation, orientation, and landing) in the absence and presence of olfactory cues is summarized. Movement toward an odor source is effected inter alia through optomotor-steered, upwind anemotaxis. It is still unclear how tsetse employ upwind anemotaxis to realize host location, considering the often highly variable wind direction. Olfactorily induced activation is governed by the olfactory cue perceived and threshold levels set by the internal state of the fly. The former depends on the odor source and distance from it; the latter is determined by species, sex, and physiological state. Wind direction and speed, as well as vegetation and the mobility of the host, interfere with successful completion of odor-induced host location. Close-range olfactory cues (including composition and concentration gradients), visual cues, and nutritional state determine whether a fly, having reached the host animal, will land on it. Carbon dioxide is important in host location because it induces landing and long-range attraction. The role of the other kairomones (acetone, 1-octen-3-ol, 4-methyl-phenol, and 3-n-propyl-phenol) is less clear. Apart from the complacency of various host species under tsetse attack, host choice by tsetse is predominantly opportunistic and primarily the result of the frequency of successful tsetse–host encounters. Nevertheless, host selection based on olfactory cues cannot be ruled out.