Detection and widespread distribution of sodium channel alleles characteristic of insecticide resistance in Culex pipiens complex mosquitoes in China.

Culex pipiens complex mosquitoes are widely distributed throughout China and are known to be important disease vectors. Two pyrethroid resistance associated mutations have been identified in Cx. pipiens complex (Diptera: Culicidae), but there is little information on the diversity and distribution of kdr alleles in pyrethroid resistance in Cx. pipiens complex mosquitoes in China. In the present study, we report on a modified three tube allele-specific (AS)-PCR method for detecting the 1014F and 1014S alleles. The new technique was applied to identify the distribution of the two alleles in natural Cx. pipiens complex populations in China. The results confirmed that the new method is both sensitive and specific. The 1014F allele was found in all 14 of the field populations tested (frequency ranged from 6.8 to 76.2%) and the 1014S allele was found in almost two-thirds (frequency from 2.4 to 28.6%), indicating that the genotypes known to be associated with pyrethroid resistance are widespread in China. The resistance-associated alleles were more common in southern Chinese sampling sites than in northern sites. The coexistence of the two resistant mutations in individual mosquitoes was also observed in five of the field populations. Two alternative mutations within the L1014 codon were identified in Culex pipiens molestus Forskal, 1775, including a non-synonymous mutation resulting in a 1014C substitution.

Reversible changes in brain glucose metabolism following thyroid function normalization in hyperthyroidism.

BACKGROUND AND PURPOSE: Patients with hyperthyroidism frequently present with regional cerebral metabolic changes, but the consequences of endocrine-induced brain changes after thyroid function normalization are unclear. We hypothesized that the changes of regional cerebral glucose metabolism are related to thyroid hormone levels in patients with hyperthyroid, and some of these changes can be reversed with antithyroid therapy. MATERIALS AND METHODS: Relative regional cerebral glucose metabolism was compared between 10 new-onset untreated patients with hyperthyroidism and 20 healthy control participants by using brain FDG-PET scans. Levels of emotional distress were evaluated by using the SAS and SDS. Patients were treated with methimazole. A follow-up PET scan was performed to assess metabolic changes of the brain when thyroid functions normalized. RESULTS: Compared with controls, patients exhibited lower activity in the limbic system, frontal lobes, and temporal lobes before antithyroid treatment. There were positive correlations between scores of depression and regional metabolism in the cingulate and paracentral lobule. The severity of depression and anxiety covaried negatively with pretreatment activity in the inferior temporal and inferior parietal gyri respectively. Compared with the hyperthyroid status, patients with normalized thyroid functions showed an increased metabolism in the left parahippocampal, fusiform, and right superior frontal gyri. The decrease in both FT3 and FT4 was associated with increased activity in the left parahippocampal and right superior frontal gyri. CONCLUSIONS: The changes of regional cerebral glucose metabolism are related to thyroid hormone levels in patients with hyperthyroidism, and some cerebral hypometabolism can be improved after antithyroid therapy.

Control of Culex quinquefasciatus in a storm drain system in Florida using attractive toxic sugar baits.

Attractive toxic sugar baits (ATSBs) were used to control mosquitoes in the storm drains of a residential area on the outskirts of St Augustine, Florida. The drainage system was newly constructed and no mosquitoes were breeding inside it. The area covered by the storm drains was divided in half; 10 drains served as control drains and 16 drains served as experimental drains. The baits, which consisted of a mixture of brown sugar, fruit juice, green dye marker and boric acid, were presented at the entrances of the treated drains and exit traps were positioned over the drain openings and the connecting tubes leading to retention ponds. Similar baits with orange dye and without toxin were presented at the entrances of control drains. A total of 220 pupae of Culex quinquefasciatus (Diptera: Culicidae) were released in each control and toxin-treated drain, and the numbers of recovered mosquitoes were examined to determine the effectiveness of ATSBs in the storm drain system. An average of 178.2 mosquitoes exited each drain in the control area; 87.0% of these had fed on the baits and were stained orange, whereas 13.0% were unstained. In the toxin-treated drains, 83.7% of hatched females and 86.6% of hatched males were controlled by the baits.

Laboratory and field evaluation of insect repellents as oviposition deterrents against the mosquito Aedes albopictus.

Three experimental approaches were used to evaluate the oviposition deterrency of three insect repellents, AI3-35765, AI3-37220 (piperidine compounds), and the standard N,N-diethyl-3-methylbenzamide (deet) to the mosquito Aedes albopictus Skuse (Diptera: Culicidae). Against laboratory-reared Ae. albopictus gravid females, the EC50 values of AI3-37220, AI3-35765 and deet were 0.004%, 0.008% and 0.011% in laboratory cages and 0.004%, 0.01% and 0.009% in an outdoor screened cage. For a natural population of Ae. albopictus tested in the field, the EC50 values were determined as 0.004%, 0.008% and 0.001%, respectively. Ageing concentrations of 0.1% of each repellent provided >50% effective oviposition deterrency against the laboratory population of Ae. albopictus for 13 days in laboratory cages, for 15 days in the outdoor cage, and for 21 days against field population of Ae. albopictus in Florida. These topical skin repellents are effective oviposition deterrents for Ae. albopictus when employed at relatively low application rates.

Laboratory and field evaluation of insect repellents as larvicides against the mosquitoes Aedes albopictus and Anopheles albimanus.

Acute toxicity and persistence of three insect repellents, deet and two piperidines (AI3-35765 and AI3-37220), were evaluated against mosquito larvae of Aedes albopictus (Skuse) and Anopheles albimanus Wiedemann (Diptera: Culicidae) in the laboratory, and against natural populations of Ae. albopictus in the field. In laboratory studies, the LC50 values of the repellents for first instars ranged between 0.005 and 0.021% (Ae. albopictus) and between 0.01 and 0.014% (An. albimanus) and, for fourth instars, between 0.019 and 0.034% (Ae. albopictus) and between 0.015 and 0.024% (An. albimanus). A 0.1% concentration of deet caused 90-100% mortality in first-instar Ae. albopictus for 4 weeks, whereas AI3-35765 and AI3-37220 at the same concentration killed 95-100% of larvae for 12 weeks and 98-100% of larvae for 33 weeks post-treatment, respectively. Deet and AI3-35765 at 0.1 % concentration resulted in complete mortality of first-instar An. albimanus for 3 weeks post-treatment, whereas AI3-37220 resulted in 91-99% larval mortalities for 35 weeks post-treatment. A 0.1% concentration of A13-37220 provided 77-98% larval mortality for 20 weeks and 63-97% larval mortality for 12 weeks post-treatment, respectively, against fourth-instar Ae. albopictus and An. albimanus. In the field, in artificial containers, the reduction of Ae. albopictus larvae caused by deet, AI3-35765 and AI3-37220 was 88-95% for 3-4 weeks, 98-100% for 7 weeks, and 82-100% for 13 weeks post-treatment, respectively. In used tyres, the same concentration of the repellents resulted in 100% reduction of Ae. albopictus larvae for 2 weeks (deet), 4 weeks (AI3-35765) and 5 weeks (AI3-37220) post-treatment. In cemetery flower vases, Aedes spp. larvae were eliminated for 4 weeks (deet) and 6 weeks post-treatment by both A13-35765 and AI3-37220. These topical repellents (particularly AI3-37220) have good potential for development and use in the management of container-inhabiting mosquitoes because they deter oviposition and kill larvae.

Effects of partial blood engorgement and pretest carbohydrate availability on the repellency of deet to Aedes albopictus.

The pretest availability of 10% sucrose solution and/or partial blood engorgement in Aedes albopictus Skuse significantly influenced mosquito attack rates and the time of repellent protection in laboratory bioassays. In 46 cm L x 38 cm W x 37 cm H cages used in USDA repellent tests, non-blood-fed and partially blood-fed mosquitoes attempted to bite at similar rates. In small cages (5 cm dia. x 4 cm H), holding individual females, mean mosquito attack rates were reduced when females were partially blood fed, compared with those not blood fed. The protection period from bites by Ae. albopictus using 25% ethanolic deet (N,N diethyl-3-methylbenzamide) increased significantly in small and USDA standard cages when females had pretest access to sucrose solution, compared with females starved for 12 h. Partial blood engorgement in mosquitoes affected repellent protection time in USDA standard test cages but not in small cages.

Diel patterns of pupation, emergence, and oviposition in a laboratory population of Aedes albopictus.

There was no apparent daily pattern of pupation in Aedes albopictus in the laboratory [14:10 h (L:D); lights on: 0600 h, lights off: 2000 h], but diel patterns of emergence and oviposition were influenced by mosquito body size. Emergence rate was highest in large-bodied male mosquitoes at 1600 h and in small males at 1000 h but was lowest in large and small males, respectively, at 2400 h and 0200 h. Peak emergence of females was at 1600 h, regardless of body size; lowest emergence was at 0400 h. Half of all ovipositions by large females in their first gonotrophic cycle (GC1) were at 2000 and 2200 h but at 1800 to 2000 h in the second gonotrophic cycle (GC2). In small females, oviposition in GC1 and GC2 was highest at 1800 and 1600 h, respectively, and lowest at 0400 h. Half of all ovipositions in small females were at 1600 to 1800 h.

Larval case-making behavior of a pestiferous chironomid, Glyptotendipes paripes (Diptera: Chironomidae), with sand grains of different sizes.

Field-collected 4th-instar Glyptotendipes paripes larvae from a natural lake in central Florida preferred small-sized (< 0.84-1.99-mm-diam) grains of sand to burrow in and make cases in the laboratory. The larvae buried or formed cases within 3 h of introduction into 120-ml paper cups containing 80 ml tap water and 20 g of the small-diameter sand. When placed in sand with grains of different size ranges, 98-100% of the larvae constructed cases in sand < 0.84 mm in diameter, whereas 86% of these larvae built cases in 0.85-1.99-mm-diam sand. The larvae were unable to construct any recognizable cases in coarser sand (2-3-mm diam). The lengths of cases built with smaller sand grains were significantly longer than those constructed in the larger grains used in the experiment. For laboratory colonization and insecticidal bioassay purposes using G. paripes larvae, sand grains < 0.84 mm in diameter should be utilized for better acclimation of the larvae.

Human host avidity in Aedes albopictus: influence of mosquito body size, age, parity, and time of day.

Diel patterns of human host attack by Aedes albopictus in the laboratory were studied in relation to mosquito body size, age, parity, and time of day. Analysis of responses in 10-, 15-, and 20-day-old females indicated a significant main effect due to time of observation in the diel period, as well as significant time x parity and time x age interactions. The distribution of mean host attack responses during the diel period was bimodal with approximately 70% of all activity during photophase (0800-2000 h); attack rates were highest in the morning (0800 h) and evening (1400-2000 h) and lowest between 0200 and 0600 h. The diel pattern of attack responses was bimodal for nulliparous and parous females, but parous females were more active than nulliparous females between 1400 and 2000 h. This pattern became increasingly bimodal during photophase, as mosquitoes aged, regardless of mosquito body size or parity. Variations in host avidity patterns between young and old females suggest that mosquito repellent bioassays initiated early in the day, that last > or = 6 h, or that use young females (approximately 5 days old) overestimate the protection period of deet against mosquitoes > 10 days old.

Age and body size effects on blood meal size and multiple blood feeding by Aedes aegypti (Diptera: Culicidae).

Ten-day-old, parous Aedes aegypti (L.) had a higher threshold of blood meal size for the inhibition of continued host-seeking than did 5 d-old, nulliparous females of the same size. Older females of a smaller-bodied cohort had a higher threshold of blood meal size for the initiation of egg development than did younger females. In contrast, older larger-sized females had a lower blood meal-size threshold for egg development. The blood of paired avian hosts was marked with rubidium and cesium to study the effect of age and body size on the frequency of multiple blood feeding. Chronologically old females had a higher frequency of multiple blood feeding than younger females. In the laboratory, the frequency of multiple blood feeding among larger-sized females was higher than among small-sized females.

Influence of body size and age of Aedes albopictus on human host attack rates and the repellency of deet.

Human host attack rates and the repellency of deet (25% in ethanol) to nulliparous Aedes albopictus in the laboratory were significantly influenced (P = 0.05) by mosquito age and body size and by the interaction of age and body size. Host attack rates were higher for 20-day- (24.5%) and 15-day-old females (22.9%) than for 10- (15.1%) and 5-day-old females (11.0%), regardless of body size, and for large females (22.2%) compared with small females (16.6%), regardless of mosquito age. Deet on human skin repelled small-bodied females longer (3.87 h) than large females (2.31 h); 15-day-old females were repelled longer (3.75 h) than 5- (2.33 h), 10- (3.08 h), or 20-day-old females (3.07 h), regardless of body size. Host attack rates and deet repellency among 15-day-old parous and 15-day-old nulliparous large- and small-bodied female Ae. albopictus were similar but deet repellency was less (by approximately 2 h) against large females compared with small-bodied females.

Comparative toxicity of selected larvicides and insect growth regulators to a Florida laboratory population of Aedes albopictus.

Five organophosphates (OPs) (chlorpyrifos, chlorpyrifos methyl, fenthion, malathion, and temephos), 3 pyrethroids (bifenthrin, cypermethrin, and permethrin), and 2 microbial pesticides (Bacillus thuringiensis serovar.israelensis [B.t.i.] and Bacillus sphaericus) were tested as larvicides against a Florida Aedes albopictus population colonized in the laboratory. In addition, 3 insect growth regulators (IGRS) (diflubenzuron, methoprene, and pyriproxyfen) were evaluated. All OPs, except for malathion, were highly effective as indicated by low LC90s ranging from 0.0069 ppm (chlorpyrifos) to 0.026 ppm (fenthion); the larvae were considered tolerant to malathion (LC90 = 1.043 ppm). LC90 values of pyrethroids were: 0.0175 ppm (bifenthrin), 0.0079 ppm (cypermethrin), and 0.0031 ppm (permethrin). Commercial products of B.t.i., Vectobac and Bactimos were considered economically effective against Ae. albopictus larvae but products of B. sphaericus were ineffective (LC90s > 28 ppm). The IGRs showed exceptional activity. Pyriproxyfen (LC90 = 0.000376 ppm), was 2.23 and 21.5 times more toxic than diflubenzuron and methoprene, respectively. In general, toxicity ranking of chemicals and microbials tested was: IGRs > pyrethroids > OPs > microbials.

Evaluation of granular corncob formulations of Bacillus thuringiensis serovar israelensis against mosquito larvae using a semi-field bioassay method.

A semi-field bioassay method using commonly available laundry tubs evaluated efficacy and residual activity of 6 granular corncob formulations of Bacillus thuringiensis serovar israelensis against laboratory-reared late 3rd- and early 4th-instar larvae of Aedes taeniorhynchus introduced to the tubs. These formulations produced appreciable larval mortalities (up to 75%) for 9 days posttreatment, with indications of having more prolonged activity. The consistent posttreatment larval mortality trends and the elucidated efficacy differences between formulations suggest that this bioassay method for the granular formulations is reliable and reproducible.

Oviposition, hatching, and age composition of a pestiferous midge, Glyptotendipes paripes (Diptera: Chironomidae).

Field-caught gravid female Glyptotendipes paripes in central Florida laid a single egg mass each during onset of photophase in laboratory cages. Egg masses averaged 626 and 942 eggs/mass during summer and spring, respectively. Oviposition preference in water was not detected when provided from different sources (i.e., distilled, tap, ponds and a lake). However, the percentage of egg hatch/mass was significantly (P < 0.05) higher in the lake water than in water from the other 3 sources. Observations on follicular development in the ovaries indicated presence of 1/2-3/4 yolk within 2 days, full yolk at > or = 2 days, and parity at > or = 4 days postemergence. Age composition of field-collected G. paripes populations from June to December 1992 was 29% at < 2, 48% at > or = 2, and 23% at > or = 4 days old, and parity 23%. Adult abundance was correlated with prevailing air temperatures in the study area.

Relationship between wing length and fecundity of a pestiferous midge, Glyptotendipes paripes (Diptera: Chironomidae).

The relationship between body size and fecundity of adult female Glyptotendipes paripes collected along southern shore areas of Lake Monroe, Sanford, FL, was studied by measuring wing length and examining ovaries, follicular development, and number of eggs/egg mass. Wing length of nulliparous, as well as parous females, had a significant (P < 0.01) linear relationship with dry body weight. Large females had a significantly (P < 0.01) higher number of follicles and eggs/egg mass than small females. No correlation existed between wing length and parity nor between wing length and age composition of field populations sampled between January and June 1993.

Efficacy of two formulations of the insect growth regulator, pyriproxyfen (Nylar or Sumilarv), against nuisance Chironomidae (Diptera) in man-made ponds.

A juvenoid insect growth regulator, pyriproxyfen (Nylar or Sumilarv), in a 10% emulsifiable concentrate (10 EC) and a granular (3% sand granules) formulation was evaluated for efficacy against natural populations of chironomid midges in man-made ponds in central Florida. Both formulations at 0.05 kg AI/ha induced complete suppression of adult midge emergence for 1 wk. At 0.2 kg AI/ha, emergence of adult midges completely ceased for 2 and 5 wk with the EC and the granules, respectively. The EC formulation was not effective beyond 2 wk, but the granules at both treatment rates reduced midge emergence by 81-100% for 9 wk posttreatment. The differences in suppression of adult midge emergence between the 2 formulations and times posttreatment were both highly significant (P < 0.01). No significant difference (P > 0.05) was found between the posttreatment percent inhibition of midge emergence caused by the lower and the higher rates of the granular formulation. Some reductions of midge larvae occurred in the ponds receiving the higher rate of the 2 formulations, but these reductions were statistically not significant.