A theoretical analysis of the feasibility of controlling tick populations (Ixodidae) by the release of reared Ixodiphagus parasitoids in tick ecosystems yielded promising results. The analysis suggested that if reasonable progress could be made in mass-rearing the parasitoids, it would be possible to control the blacklegged tick, Ixodes scapularis (Say), the vector of Lyme disease, by this biological control procedure. Lyme disease has become the most important vector-borne disease in the United States. In a field-release experiment conducted in Africa by members of the International Center for Insect Physiology and Ecology, effective control of Amblyomma variegatum (F.) was obtained by the release of Ixodiphagus parasitoids in tick habitats. Encouraging theoretical results along with the encouraging results of a field-release experiment indicate the need for civil and political leaders in countries where ticks are a major problem to sponsor strong and well-coordinated research initiatives focused on the development of this new method of dealing with tick problems.

The morphology of insect genitalia is often highly species-specific, and its variation has been suggested as an important impetus for evolution. Structural variation of the male genitalia and the female spermathecae in Phlebotomine sand flies is unique among the blood sucking Diptera. We describe the fine structures involved in mating for Phlebotomus papatasi (Scopoli). Relationships among the length of the spermathecal duct and aedeagal filament were studied in 26 species of Old World phelebotomine sand flies comprising 12 subgenera. In most taxa the aedeagal filaments were very long allowing direct insemination into the spermathecae, indicating that intrasexual competition among males occurs as sperm precedence. There was a positive correlation between the lengths of the spermathecal ducts and aedeagal filaments, indicating that an evolutionary “arms race” occurs between males and females over the control of fertilization. The pattern of genitalia variation in phlebotomine sand flies also indicated that differences in the lengths of the spermathecal ducts and aedeagal filaments are distributed unevenly among closely related species. Genital differences do not seem to occur in populations of the Phlebotomus argentipes Annandale & Brunetti complex, whereas differences showed strongly in closely related Phlebotomus papatasi and P. bergeroti Parrot, and in sympatric Phlebotomus martini Parrot and P. celiae Minter.

Aedes aegypti (L.), Culex sitiens Weidemann, Culex annulirostris Skuse, and Culex quinquefasciatus Say mosquitoes colonized at the Queensland Institute of Medical Research, Brisbane Australia, were fed on blood containing Barmah Forest virus (BF). Only Cx. annulirostris was susceptible to infection, with a median cell culture infectious dose (CCID₅₀) of 10^3.36 per mosquito. Ae. aegypti and Cx. quinquefasciatus were infected experimentally, but at rates of <9%. Cx. sitiens did not become infected. Infection rates for Cx. annulirostris fed 10^3.5 CCID₅₀ of virus per mosquito, varied from 9 to 50% between 2 and 13 d after infection. Virus transmission to suckling mice by Cx. annulirostris occurred from 2 d after infection. Transmission of BF virus by Cx. annulirostris was 10% at 2 d after infection and did not exceed 8% thereafter. Although Cx. annulirostris may be infected and is able to transmit BF virus to suckling mice, it is nonetheless a relatively inefficient vector of the virus.

Several highland regions of Africa recently have suffered malaria epidemics. Because malaria transmission is unstable and the population has little or no immunity, these highlands are prone to explosive outbreaks when densities of Anopheles exceed critical levels and conditions favor transmission. If an incipient epidemic can be detected early enough, control efforts may reduce morbidity, mortality, and transmission. Here we present three methods (direct, minimum sample size, and sequential sampling approaches) that could be used to determine whether the household indoor resting density of Anopheles gambiae s.l. has exceeded critical levels associated with epidemic transmission. Data on Anopheles density before, during, and after a malaria epidemic (December 1997–July 1998) in the highlands of southwestern Uganda were evaluated to demonstrate the application of these three approaches. During this epidemic, a density of 0.25 Anopheles mosquitoes per house was associated with epidemic transmission, whereas 0.05 mosquitoes per house was chosen as a normal level expected during nonepidemic months. The direct approach to calculating mean Anopheles density with an allowable error of 20–50% of the mean would require the sampling of 102–16 houses, respectively. In contrast, with only seven houses, the minimum sample size approach could be used to determine whether Anopheles density had exceeded the critical level. This method, however, would result in an overestimation of the risk of an epidemic at low Anopheles density. Finally, a sequential sampling plan could require as many as 50 houses to conclude that risk of an epidemic existed, but this disadvantage is offset by the ability to preset the probabilities of concluding that risk of an epidemic exists at both the critical and normal Anopheles densities. Our study illustrated that it is feasible, and probably expedient, to include monitoring of Anopheles density in highland malaria epidemic early warning systems.

Seasonal abundance and survivorship of Culicoides sonorensis Wirth & Jones were examined at a dairy in southern California from January 1995 to December 1997. Insects were collected one to two times per week using five CDC-type suction traps (without light) baited with CO₂ at a constant release rate of 1,000 ml/min. Female and male abundance was greatest during late summer and early fall and was directly correlated with mean monthly air temperature. Parity of females was lowest during late summer and early fall. The gonotrophic cycle was estimated to require 3–4 d during hot summer months and up to 14 d during cool winter months. Estimated extrinsic incubation of bluetongue virus (BLU) was 9–10 d during August and September. The estimated daily survival ranged from <60% in the summer to >95% in the winter, resulting in an expectation of life of only 2–3 d in summer and >10 d in winter. The probability of females surviving the extrinsic incubation period for BLU virus, and the expectation of infective life were both lowest during late summer and early fall. During 1997, midge abundance during late summer was not high enough to overcome very low survivorship, and the absolute number of females expected to survive the extrinsic incubation period was relatively low. However, in 1995 and 1996, very high midge abundance compensated for low survivorship during summer and the number of females expected to survive the extrinsic incubation period was relatively high. Although abundance was generally very low during the cool winter and spring, host-seeking females were captured throughout the year, and their winter survival was high. Overwintering of BLU virus by continued transmission of the virus by active midges appears possible.

Effects of temperature and pH on the catalytic properties of hexokinase (HK, EC 2.7.1.1) from the flight muscles of Dipetalogaster maximus (Uhler) were studied. The enzyme showed a hyperbolic behavior with its two substrates (glucose and ATP). There was no inhibition by glucose. Apparent Km and Vmax increased as pH increased from 7.0 to 8.5. Catalytic efficiency was lowest at pH 7.0. Km, Vmax, and catalytic efficiency were higher at 37°C than at 30 and 20°C. There was marked inhibition by ATP, which was dependent on pH and temperature. Km values for ATP were reduced and catalytic efficiency increased as pH increased. Lowest Vmax was observed at pH 7.0. At this pH there was 87.3% inhibition by ATP, whereas it was only 5.7% at pH 8.5 (at 30°C). Km, Vmax, and catalytic efficiency were higher at 37°C than at 30 and 20°C. The strong inhibition by ATP detected at 20°C (pH 7.6) almost disappeared at 37°C. Therefore, temperature could regulate hexokinase activity by modulating the inhibition produced by ATP. Glucose utilization and ATP production would be promoted when temperature rises from 30 to 37°C. Because insect thoracic muscles increase their temperature over 30°C during flight, this phenomenon elucidates a mechanism enhancing energy supply for muscle activity.

Numbers and the distribution of third-stage larvae (L3) were investigated in Aedes sollicitans (Walker) and Aedes taeniorhynchus (Wiedemann) female mosquitoes fed Dirofilaria immitis (Leidy) infectious-blood with densities of microfilariae (mf) ranging from ≈7,100–43,400 mf/ml. At each microfilarial density, a maximum of 63–66 infective larvae were recovered from an Ae. sollicitans alive on day 15 after infection. In comparison with Ae. taeniorhynchus, Ae. sollicitans averaged greater numbers of L3 and from 1.4 to 2.4 times more L3 in the head and labium per infected female. The trend was for greater numbers of L3 to be found in the labium than in the head of Ae. sollicitans, but there were no significant differences between numbers of L3 recovered from these sites in differentially infected females. However, numbers of L3 recovered from the head versus the labium of differentially infected Ae. taeniorhynchus varied significantly with the infectious blood microfilarial density. At the two lowest and highest microfilarial densities, greater numbers of L3 were recovered from the head and labium, respectively. Variations among species in the female body size, blood meal size, and retention of L3 may be factors responsible for differences observed between the total numbers and percentage distribution of D. immitis L3 recovered from the simultaneous blood-fed Ae. sollicitans and Ae. taeniorhynchus.

The effect of eastern equine encephalomyelitis (EEE) virus on the survivorship of Aedes albopictus (Skuse), Anopheles quadrimaculatus Say, and Coquillettidia perturbans (Walker) was determined experimentally. Female mosquitoes were allowed to feed on EEE viremic chicks, and survival rates were compared for infected and uninfected mosquitoes. Additionally, the survival of female Cq. perturbans and An. quadrimaculatus intrathoracically (IT) inoculated with EEE was compared with controls receiving diluent inoculations. Infection with EEE significantly reduced survival in Cq. perturbans compared with uninfected individuals in per os infection experiments. IT infections of Cq. perturbans did not reduce survival when compared with diluent inoculated groups. In contrast, infection with EEE did not affect the survival of Ae. albopictus after per os infection or An. quadrimaculatus after either IT or per os infections.

Two previously undescribed rickettsiae were detected in Ixodes ricinus Ricketts by polymerase chain reaction. Ixodes ricinus Slovakia (IRS)3 and IRS4 were identified in ticks collected in northeastern and southwestern Slovakia, respectively. Sequences of the 16S rRNA citrate synthase (gltA) and outer membrane protein rOmpA (ompA) encoding genes of both strains were nearly identical but were distinct from those of all other known rickettsiae. Phylogenetic relationships inferred from the comparison of these sequences with those of other members of the genus Rickettsia indicate that IRS3 and IRS4 constitute a new rickettsial genotype and form a separate cluster among the spotted fever group rickettsiae.

The life cycle of Ixodes (Ixodes) loricatus Neumann, reared in the laboratory, is described. Engorged females collected from opossums trapped in the states of Minas Gerais and São Paulo, Brazil, which were used to start the laboratory colonies, were designated as BMG and CSP, respectively. Larval and nymphal ticks from both colonies fed separately on Rattus norvergicus Berkenhout or Calomys callosus Rengger, whereas Didelphis marsupialis L and Didelphis albiventris Lund were used as hosts for BMG and CSP adults, respectively. Biological and developmental data obtained from ticks of both the BMG and CSP colonies that were reared separately for two consecutive generations were compared. The percentage of fed or molted ticks reared on C. callosus was higher than that recorded for ticks fed on R. norvergicus in the majority of the observations. Despite significant differences among several of the biological parameters, the pattern of the life cycles of the two tick colonies was similar. Results indicated that the mean life cycle duration of I. (I.) loricatus was ≈7 mo from parental oviposition to the occurrence of F₁ eggs, regardless of geographic origin or host species.

Permethrin-resistant colonies of Pediculus capitis (De Geer) from Buenos Aires were used to establish a resistance profile and to examine resistance mechanisms. All permethrin-resistant head lice (resistance ratio from 52.8 to >88.7) were also resistant to d-phenothrin (resistance ratio from 40.86 to >48.39) and deltamethrin (resistance ratio from 16.24 to 38.06). No cross-resistance to carbaryl was found in any of the pyrethroid-resistant P. capitis tested. Otherwise, all resistant colonies showed low to high levels of resistance to β-cypermethrin. This pyrethroid had never been applied as a pediculicide in Argentina; however, the high level of resistance found in these permethrin-resistant colonies (resistance ratio from 9.74 to 50.97) demonstrated that pyrethroid cross-resistance occurred to this novel insecticide. Treatment with piperonyl butoxide (PBO) or triphenylphosphate (TPP) significantly decreased the toxicity of permethrin in the four colonies tested. The esterase inhibitor TPP produced lower enhancement of toxicity than the multifunction oxidase inhibitor PBO in the colonies having the highest resistance levels. Results presented here concerning the cross-resistance profile and synergism by enzyme inhibitors in permethrin-resistant head lice demonstrated that enhanced metabolism was involved in the pyrethroid resistance. However, the substantial degree of resistance that remained after synergism suggested the presence of another resistance mechanism. Cross-resistance to pyrethroid and susceptibility to the carbamate carbaryl suggested a common action mechanism.

During the first ovarian cycle, autogenous female mosquitoes develop their ovaries in the absence of blood feeding. In autogenous Culex pipiens molestus (Forskal), complete yolk deposition was observed 2 d after emergence, even when no feeding was allowed (starved). Neutral lipids in Cx. p. molestus increased during the pupal stage, abruptly declined after emergence, and again increased on day 3. In contrast, neutral lipids decreased in anautogenous Anopheles stephensi (Liston) and Cx. p. pallens (Coquillett) and starved females died within 2–3 d after emergence. High ratios of two major neutral lipids, free fatty acid and triglyceride, were isolated by thin-layer chromatography (TLC) from the lipid contents of both Cx. p. molestus and An. stephensi fourth- instars and newly emerged females. Fatty acid analyses using gas liquid chromatography (GLC) and GLC-mass spectrometry (GLC-MS) showed higher proportions of unsaturated than saturated fatty acids in Cx. p. molestus at both stages and two major neutral lipids: free fatty acids and triglycerides. The percentage composition of linoleic acid (C18:2), which is a precursor of arachidonic acid, was higher in Cx. p. molestus than in An. stephensi. Our results indicated that elevated lipid content before emergence may play a role of inducing ovarian development in autogenous mosquitoes.

The effects of larval densities of one to four individuals in standard Drosophila-vials (diameter 25 by 95 mm) on the age at pupation, starved dry weight, and wing length of Culex pipiens quinquefasciatus Say were studied. This approach required relatively few larvae per replicate and included a control treatment, where individual larvae developed in the absence of competition. This design also tested for competitive interactions between male and female larvae. Mosquitoes pupated later, and emerged with lighter starved dry adult weight and shorter wings as larval density increased. The size of adult female mosquitoes, particularly their starved dry weight, was sensitive to larval density and also was influenced by the presence or absence of competition with another female larva. In contrast, the life history traits of males did not vary as a function of competition with female larva. Female larvae were also more likely to die in the highest density treatment. This design confirmed previous results and offered a potentially useful experimental approach to investigate the effects of density-dependent competition among mosquito larvae.

Japanese encephalitis is a disease of major importance in Asia, which from 1995 has extended its range into the north of Australia. Culex annulirostris Skuse of the Culex sitiens subgroup of Culex was incriminated as the most likely mosquito vector. Because misidentifications previously have occurred within this subgroup, our paper defines electrophoretic methods to identify Culex specimens from Queensland and the Northern Territory in Australia and from Western Province in Papua New Guinea. In collections from 1996 to 1998 Culex sitiens Wiedemann, Cx. palpalis Taylor, and Cx. annulirostris comprised 93.1% of the total banded proboscis Culex mosquitoes collected; 6.9% remained unidentified to species by morphological or electrophoretic examination. The prevalence of Cx. palpalis was variable and appeared to be associated with below average rainfall during 1997. In Papua New Guinea, this species comprised up to 97.4% of banded proboscis Culex, with smaller numbers collected from the Torres Strait Islands and Cape York; none was collected from other Queensland localities. Cx. annulirostris was more prevalent during years of average or above average rainfall and was predominant in most localities, especially in the Torres Strait and Queensland. These data confirmed the problems in separating Cx. sitiens from Cx. palpalis and Cx. annulirostris using morphological characters.

Hyaluronidase activity in the salivary gland homogenates of Simulium vittatum (Zetterstedt) is described, and its optimal pH determined. Salivary activity was reduced significantly after a blood meal, indicating that it was secreted after blood feeding. Phlebotomus papatasi (Scopoli) also exhibited salivary hyaluronidase activity. These results indicate that hematophagous pool-feeding insects may secrete this enzyme to help the spread of salivary antihemostatic agents in the vicinity of the feeding lesion, and perhaps to increase the size of the feeding lesion itself. Additionally, this enzyme may affect local host immune reactions and promote arboviral transmission.

The mouthparts of both males and females of Lutzomyia migonei França were compared by scanning electron microscopy (SEM) and light microscopy (LM), and their structures are herein described. Mandibles are present in both sexes but in males they are reduced and, in contrast to females, no teeth were observed. As in females, the laciniae in males are highly sclerotized, but the number of lateral teeth are reduced and retrorse teeth are absent. Only females possess teeth at the tip of the hypopharynx, whereas in males they are substituted by spicula. Except for the length from the junction with the hypopharynx to the tip, which is shorter in males than in females, the labrum is similar in both sexes in terms of form and sensilla. On the labrum of males sensilla could be detected similar to the apical sensilla of females which play a role in the identification of blood.

We sampled Anopheles punctipennis (Say) from 11 localities throughout Vermont to examine the effects of latitude and two local geographical boundaries, Lake Champlain and the Green Mountains, on the population genetic structure of this species. Thirty-five mitochondrial haplotypes were detected in 104 individuals using a variable region of the COI gene. When latitude was examined, we detected significant structure within localities and among localities within latitudinal regions. For geographic analysis, significant genetic structure was detected only within localities. Estimates of gene flow across geographic regions indicate that the Green Mountains, but not Lake Champlain, is a barrier to dispersal for this species. We found no correlation between genetic and geographic distances for An. punctipennis.

Aggregation-attachment pheromones are produced only by male ticks of the genus Amblyomma that have imbibed blood for at least 8 d from their mammalian hosts. This report demonstrates that production and release of aggregation-attachment pheromones by Amblyomma maculatum (Koch) males can be induced in vitro by using nonblood media, artificially introduced through capillary tubes, into the male ticks. The presence of these pheromones is demonstrated by using both biological observations on bovine hosts and in vitro experimentation with petri dishes. The attraction of unfed female ticks to the artificially fed males (using the petri dish method) was significantly higher (P < 0.001) than the attraction of unfed females to unfed males. Similarly, attraction and attachment were recorded on bovine hosts. Only 62.8 ± 17.5% of the females released attached to the bovine host. Of these, 61.9 ± 19.37% attached around artificially fed males that were placed on the bovine 24 h earlier. This percentage did not differ significantly from the 81.4 ± 7.1% of the total that attached around males that fed naturally for 8 d. In comparison, only 33.3 ± 21.9% of the total number of females placed on the host did so after being fed 1 d (control group). The possibility of using capillary feeding as a new tool for investigating the physiology and reproductive behavior of blood- sucking arthropods is discussed.

The vector competence of Ixodes muris (Bishopp & Smith) was determined for Borrelia burgdorferi, the etiologic agent of Lyme disease. Larval I. muris were fed on ICR outbred mice infected with the B-31 laboratory strain of B. burgdorferi. Replete larvae, at 5 d after feeding, were assayed for infection by culture in Barbour-Stoner-Kelly (BSK-H) media. Infection frequency in I. muris replete larvae was 66%. Resultant nymphs were fed on naive ICR outbred mice to determine the ability of I. muris to transmit infection. Infection frequency in fed nymphs declined to 38% and only 1/5 mice was positive for B. burgdorferi on ear biopsy culture. We demonstrated that I. muris is capable of acquiring and transmitting B. burgdorferi but is a relatively poor vector compared with I. scapularis (Say).

Attempts were made to use pteridine fluorescence levels as a tool for aging individual Aedes polynesiensis Marks and Culex quinquefasciatus Say mosquitoes. Fluorescent pigments were extracted and quantified with techniques and apparatus (i.e., a spectrofluorometer) that can be used in developing countries or in field laboratories, and that has already given consistent results in similar studies on other insect groups. However, for Ae. polynesiensis as well as Cx. quinquefasciatus, individual fluorescence measurements were mostly below the spectrofluorometer white noise level. With batches of Aedes or Culex of the same age, significant fluorescence levels were recorded but not in relation to their calendar ages. The low content of pteridines in mosquitoes suggests that standard spectrofluorometry is not sufficiently sensitive for such studies.

A survey of 124 dogs for ticks was conducted from August to November 1998 in 68 small farms of Uruará municipality in Eastern Amazon-Brazil. We collected 55 ticks from 18 dogs (14.5%). Amblyomma oblongoguttatum Koch, Amblyomma ovale Koch, and Amblyomma cajennense (F.) were found on nine, six, and one dog, respectively. Fourteen small farms (20.5%) had at least one dog with ticks.

During a survey conducted from August to November 1998 of ticks associated with dogs in the rural area of Uruará, in the state of Para, Eastern Amazon region of Brazil, we collected one gynandromorph specimen out of 18 Amblyomma oblongoguttatum Koch specimens collected from dogs. It is a perfect bipartite gynandromorph, reported in this species for the first time.

Laboratory strains of Culex pipiens molestus Forskal and Culex tritaeniorhynchus Giles from northern Taiwan were compared for their susceptibility to the Sanhsia MQ1–2 (SH) strain of Japanese encephalitis (JE) virus isolated from Taiwan. After feeding on a sweetened blood–virus mixture, viral titers in Cx. p. molestus during the 14-d incubation period ranged from a minimum of 2.9 log₁₀PFU (plaque forming units) per mosquito on day 3 after ingestion to a maximum of 4.65 log₁₀PFU at day 8 and in Cx. tritaeniorhynchus from 2.6 on day 10–5.18 log₁₀PFUper mosquito on day 13. Although virus titer in Cx. p. molestus was lower than in Cx. tritaeniorhynchus at the end of the experiment, this difference was not statistically significant. The median infective dose (ID₅₀) for Cx. p. molestus was 2.83 log₁₀PFU and for Cx. tritaeniorhynchus was 1.02 log₁₀PFU per mosquito, and this difference also was not significant. There also was no significant difference between the median infective dose for transmission (TID₅₀) per mosquito for Cx. p. molestus (5.34 log₁₀PFU) and Cx. tritaeniorhynchus (4.59 log₁₀PFU). We concluded that Cx. p. molestus is an effective laboratory vector of JE virus.

Vesicular stomatitis virus serotype New Jersey (VSNJV) was mixed with bovine blood or fetal bovine serum (FBS) and fed across silicone membranes to laboratory populations of Culicoides sonorensis Wirth & Jones. In an initial study, virus was detected after 13 d in 21% of the midges that received an FBS/VSNJV mixture. In subsequent time-course experiments, engorged females were collected and maintained at 20.0°C and assayed for VSNJV immediately after feeding and at 1, 3, 7, 10 and 13 d after feeding. Virus was detected after 13 d in 3% of the midges that received a bovine blood/VSNJV mixture and in 9% of the midges that received an FBS/VSNJV mixture. The results indicate that C. sonorensis should be considered as a potential biological vector of VSNJV.