Evaluation of boric acid as toxic sugar bait against resistant Aedes aegypti mosquitoes

Current methods of broad area application of contact insecticides used in mosquito control are becoming less effective, primarily due to resistance within mosquito populations. New methods that can deliver ingestible insecticides are being investigated as a means to mitigate resistance. This study evaluated insecticide delivery through toxic sugar baits (TSB) and resulting mortality of susceptible and resistant strains of Aedes aegypti. Two Ae. aegypti strains were evaluated using a 1% boric acid TSB: the susceptible Orlando 1952 (ORL) strain and the resistant Puerto Rican (PR) strain. The TSB resulted in high mortality for both ORL and PR strain of Ae. aegypti. Average mortality of female mosquitoes given TSB was 90.8% for PR and 99.3% for ORL. Our study suggests that targeting resistant mosquitoes with ingestible insecticides through TSBs could be a viable alternative to current mosquito control strategies and should be considered when developing an integrated vector management program.     

Behavioural and insecticidal effects of organophosphate‐, carbamate‐ and pyrethroid‐treated mosquito nets against African malaria vectors

Three insecticides – the pyrethroid deltamethrin, the carbamate carbosulfan and the organophosphate chlorpyrifos‐methyl – were tested on mosquito nets in experimental huts to determine their potential for introduction as malaria control measures. Their behavioural effects and efficacy were examined in Anopheles gambiae Giles s.s. (Diptera: Culicidae) and Anopheles funestus Giles s.s. in Muheza, Tanzania, and in Anopheles arabiensis Patton and Culex quinquefasciatus Say in Moshi, Tanzania. A standardized dosage of 25 mg/m² plus high dosages of carbosulfan (50 mg/m², 100 mg/m² and 200 mg/m²) and chlorpyrifos‐methyl (100 mg/m²) were used to compare the three types of insecticide. At 25 mg/m², the rank order of the insecticides for insecticide‐induced mortality in wild An. gambiae and An. funestus was, respectively, carbosulfan (88%, 86%) > deltamethrin (79%, 78%) > chlorpyrifos‐methyl (35%, 53%). The rank order of the insecticides for blood‐feeding inhibition (reduction in the number of blood‐fed mosquitoes compared with control) in wild An. gambiae and An. funestus was deltamethrin > chlorpyrifos‐methyl > carbosulfan. Carbosulfan was particularly toxic to endophilic anophelines at 200 mg/m², killing 100% of An. gambiae and 98% of An. funestus that entered the huts. It was less effective against the more exophilic An. arabiensis (67% mortality) and carbamate‐resistant Cx quinquefasciatus (36% mortality). Carbosulfan deterred anophelines from entering huts, but did not deter carbamate‐resistant Cx quinquefasciatus. Deltamethrin reduced the proportion of insects engaged in blood‐feeding, probably as a consequence of contact irritancy, whereas carbosulfan seemed to provide personal protection through deterred entry or perhaps a spatial repellent action. Any deployment of carbosulfan as an individual treatment on nets should be carried out on a large scale to reduce the risk of diverting mosquitoes to unprotected individuals. Chlorpyrifos‐methyl was inferior to deltamethrin in terms of mortality and blood‐feeding inhibition and would be better deployed on a net in combination with a pyrethroid to control insecticide‐resistant mosquitoes.     

Evaluation of collection methods for Culex quinquefasciatus,Aedes aegypti,and Aedes simpsoni in northeastern Tanzania

In East Africa, significant morbidity and mortality are caused by infections spread by Culex quinquefasciatus and Aedes aegypti. Sticky traps have been shown to be effective tools for sampling populations of Aedes mosquitoes and have been found to catch Cx. quinquefasciatus. Thus, they could potentially be used to sample populations of this species. This study compared Sticky ovitraps (SO) and MosquiTraps (MQT) with the CDC Gravid trap (CDC‐GT) for collection of Culex and Aedes mosquito populations in Tanzania. A follow‐up experiment was carried out using traps set for a 24‐h period to accommodate the oviposition habits of Aedes aegypti and Ae. simpsoni s.l. mosquitoes. The results showed that the CDC‐GT caught significantly more Cx. quinquefasciatus and Ae. aegypti than the SO or MQT, but there was no significant difference in the number of mosquitoes caught between the two sticky traps or of Ae. simpsoni s.l. caught among the three trap types. The results suggest that CDC‐GTs are the most appropriate in sampling of Cx. quinquefasciatus. Although CDC‐GTs collected more Ae. aegypti than the sticky traps, the simplicity and cost benefit of sticky traps facilitates large scale studies. All three trap types should be considered for monitoring Aedes mosquitoes.     

Insecticide resistance and detoxifying enzyme activity in the principal bancroftian filariasis vector, Culex quinquefasciatus, in northeastern India

The insecticide resistance status of Culex quinquefasciatus Say (Diptera: Culicidae) to DDT and deltamethrin across army cantonments and neighbouring villages in northeastern India was investigated. In India, DDT is still the insecticide of choice for public health programmes. In military stations, pyrethroids, especially deltamethrins, are used for insecticide‐treated nets (ITNs). Recent information on the levels of resistance to DDT and deltamethrin in mosquito populations of northeastern India is scare. Continued monitoring of insecticide resistance status, identification of the underlying mechanisms of resistance in local mosquito populations and the establishment of a baseline data bank of this information are of prime importance. Insecticide susceptibility assays were performed on wild‐caught adult female Cx. quinquefasciatus mosquitoes to the discriminating doses recommended by the World Health Organisation (WHO) to DDT (4%) and deltamethrin (0.05%). Across all study sites, mortality as a result of DDT varied from 11.9 to 50.0%, as compared with 91.2% in the susceptible laboratory strain (S‐Lab), indicating that Cx. quinquefasciatus is resistant to DDT. The species was found to be 100% susceptible to deltamethrin in all study sites except Benganajuli and Rikamari. Knock‐down times (KDT) in response to deltamethrin varied significantly between study sites (P < 0.01) from 8.3 to 17.8 min for KDT₅₀ and 37.4 to 69.5 min for KDT₉₀. All populations exceeded the threshold level of alpha‐esterase, beta‐esterase and glutathion S‐transferase (GST) established for the S‐Lab susceptible strain, and all populations had 100% elevated esterase and GST activity, except Missamari and Solmara. Beta‐esterase activity in Field Unit II (96.9%) was less than in any of the other populations. Benganajuli had the highest activity level for all the enzymes tested. There was a significant correlation between all enzyme activity levels and insecticide resistance phenotype by populations (P < 0.05). The results presented here provide the first report and baseline information of the insecticide resistance status of Cx. quinquefasciatus in northeastern India, and associated information about biochemical mechanisms that are essential for monitoring the development of insecticide resistance in the area.     

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.     

Haemocyte population and ultrastructural changes during the immune response of the mosquito Culex quinquefasciatus to microfilariae of Wuchereria bancrofti

Abstract Haemocytes circulating in the haemolymph protect insects against pathogens that enter the haemocoel. Changes in haemocyte morphology and differences in haemocyte counts during the immune response of Culex quinquefasciatus Say (Diptera: Culicidae) to microfilariae of Wuchereria bancrofti (Cobbold) (Spirurida: Onchocercidae) were investigated in the present study. The mean number of total haemocytes was significantly elevated in infected mosquitoes (P < 0.001), reaching a peak on the third day post‐infection. Differential counts show that mean numbers of prohaemocytes, plasmatocytes, granular cells and oenocytoids increased significantly after infection with microfilariae granulocytes compared to the control and näive groups of Cx. quinquefasciatus (P < 0.05). Changes in proportional counts of haemocytes were also analysed in haemolymph perfusates of Cx. quinquefasciatus infected with W. bancrofti. On the first day post‐infection, infected mosquitoes showed an increase in the proportion of prohaemocytes (18.8% compared to 9.6% for the control) and of oenocytoids (7.1% compared to 4.7% control); however, they exhibited lower levels of plasmatocytes (36.6% compared to 42.1% control) and granular cells (36.1% compared to 41.4% control). On day 14 post‐infection, similar changes were observed for these haemocyte types, except that the proportion of granular cells was significantly greater than the control (41.2% compared to 31.3% control). Although an enhancement of prohaemocyte numbers was observed, this cellular type did not show any ultrastructural alteration. On the other hand, granular cells, plasmatocytes and oenocytoids presented morphological alterations indicative of innate immunological activation in mosquitoes infected with W. bancrofti.     

A recent survey of mosquito fauna in Guandong Province, southern China, with a review of past records

Abstract The southern province of Guangdong has long been subject to endemic mosquito‐borne diseases. In recent years, this region of China has experienced rapid, extensive economic development involving environmental change, making much of the scant knowledge of its mosquito fauna obsolete. This paper reviews previous mosquito surveys, some of which may be too old to be of relevance to present‐day conditions, and presents the results of a recent survey of adult and immature mosquitoes. The main vectors of mosquito‐borne diseases endemic to the area, such as dengue and Japanese encephalitis virus, develop in container habitats. A three‐year survey was carried out, between 2004 and 2006, of 4131 breeding containers in residential areas and in open, sparsely populated areas, of which approximately 50% were positive for the presence of mosquitoes, and 10 156 larvae and pupae were collected and identified. Twelve species were found in both residential and sparsely populated areas: Aedes albopictus (Skuse) (Diptera: Culicidae), Ae. lineatopennis (Ludlow), Ae. vexans (Meigen), Tanakaius togoi (Theobald), Culex barraudi Edwards, Cx dispectus Bram, Cx malayi (Leicester), Cx pallidothorax Theobald, Cx quinquefasciatus Say, Cx sitiens Wiedemann, Lutzia fuscanus Wiedemann and Tripteroides bambusa (Yamada). Armigeres subalbatus (Coquillett) was found only in containers in villages, whereas Ae. macfarlanei Edwards, Cx mimeticus Noé, Cx sinensis Theobald, Cx vegans Wiedemann, Cx wilfredi Colless and Mansonia uniformis (Theobald) were found only in non‐ or sparsely populated areas. In residential areas, the rank order of most common species, as measured by the proportion of containers colonized, was Ae. albopictus > Cx quinquefasciatus > Lu. fuscanus, whereas in sparsely populated areas the rank order was Cx quinquefasciatus > Ae. albopictus > Lu. fuscanus. Light traps in non‐ or sparsely populated areas caught 5995 adult mosquitoes of 25 species, some of which are not container breeders. The most common species were: Anopheles sinensis Wiedemann, An. maculatus Theobald, An. minimus Theobald, Ta. togoi, Cx bitaeniorhynchus Giles, Cx malayi, Cx quinquefasciatus, Cx sinensis Theobald, Cx sitiens, Cx tritaeniorhynchus Giles and Lu. fuscanus. It is noteworthy that nine species caught had not been previously recorded in Guangdong Province, highlighting the deficient knowledge of the current composition and distribution of the mosquito fauna of this part of China.     

Indoor Application of Attractive Toxic Sugar Bait (ATSB) in Combination with Mosquito Nets for Control of Pyrethroid-Resistant Mosquitoes

Background

Attractive toxic sugar bait (ATSB) sprayed onto vegetation has been successful in controlling Anopheles mosquitoes outdoors. Indoor application of ATSB has yet to be explored. The purpose of this study was to determine whether ATSB stations positioned indoors have the potential to kill host-seeking mosquitoes and constitute a new approach to control of mosquito-borne diseases.

Methods

Insecticides were mixed with dyed sugar solution and tested as toxic baits against Anopheles arabiensis, An. Gambiae s.s. and Culex quinquefasciatus in feeding bioassay tests to identify suitable attractant-insecticide combinations. The most promising ATSB candidates were then trialed in experimental huts in Moshi, Tanzania. ATSB stations were hung in huts next to untreated mosquito nets occupied by human volunteers. The proportions of mosquitoes killed in huts with ATSB treatments relative to huts with non-insecticide control treatments huts were recorded, noting evidence of dye in mosquito abdomens.

Results

In feeding bioassays, chlorfenapyr 0.5% v/v, boric acid 2% w/v, and tolfenpyrad 1% v/v, mixed in a guava juice-based bait, each killed more than 90% of pyrethroid-susceptible An. Gambiae s.s. and pyrethroid-resistant An. arabiensis and Cx. quinquefasciatus. In the hut trial, mortality rates of the three ATSB treatments ranged from 41-48% against An. arabiensis and 36-43% against Cx. quinquefasciatus and all were significantly greater than the control mortalities: 18% for An. arabiensis, 7% for Cx. quinquefasciatus (p<0.05). Mortality rates with ATSB were comparable to those with long lasting insecticidal nets previously tested against the same species in this area.

Conclusions

Indoor ATSB shows promise as a supplement to mosquito nets for controlling mosquitoes. Indoor ATSB constitute a novel application method for insecticide classes that act as stomach poisons and have not hitherto been exploited for mosquito control. Combined with LLIN, indoor use of ATSB has the potential to serve as a strategy for managing insecticide resistance.     

First report of L1014F kdr mutation in Culex quinquefasciatus in Mexico

The L1014F mutation in the voltage‐sodium channel gene has been associated with resistance to DDT and pyrethroids in various arthropod species including mosquitoes. We determined the frequency of the L1014F kdr mutation in 16 field populations of Culex quinquefasciatus from Northeastern Mexico collected between 2008 and 2013. The L1014F was present in all populations analyzed with the lowest frequency (3.33%) corresponding to the population from Monclova collected in 2012, and the highest frequency (63.63%) from the Monterrey population collected in 2012. The presence of a kdr mutation in populations of Cx. quinquefasciatus from northeastern Mexico provides evidence of pyrethroid resistance. This requires a special attention, considering that pyrethroid‐based insecticides are commonly used in vector‐control campaigns, especially against Aedes aegypti (L.).     

Field evaluations of disposable sticky lures for surveillance of Aedes aegypti (Stegomyia aegypti) and Culex quinquefasciatus in Jakarta

From December 1997 to April 1998, disposable sticky lures (1608 lure days) were trialled in homes in north Jakarta, Indonesia as surveillance tools for Aedes aegypti (Stegomyia aegypti) (Diptera: Culicidae) and Culex quinquefasciatus (Diptera: Culicidae), referenced to indoor resting adult collections (92 × 10 min). The lures collected 89.4% of the total of 1339 Ae. aegypti and 92.1% of the total of 1272 Cx. quinquefasciatus collected by all methods. Because there were no significant differences with respect to numbers collected in bedrooms, living rooms and kitchens, bedrooms were selected for subsequent trials for reasons of convenience. The main trials involved a replicated complete block design with L‐lysine and sodium carbonate. Lures without attractant or with four different dilutions of L‐lysine collected 3.4–8.5 times more Ae. aegypti and 4.2–8.1 times more Cx. quinquefasciatus than were collected by mouth aspirator. Lures with or without dilutions of sodium carbonate collected 2.7–5.0 times more Ae. aegypti and 1.8–4.2 times more Cx. quinquefasciatus than aspirator collections. The precision associated with catches of sticky lures was better than that for aspirator collections. Although olfactants generally improved the numbers of mosquitoes collected, the differences in catch between lures with and without attractants were usually non‐significant. Any deficit in catch may be offset by increasing the surveillance period to ≥30 days to detect all four dengue serotypes from infected mosquitoes.     

Could resistance to insecticides in Plutella xylostella (Lep., Plutellidae) be overcome by insecticide mixtures?

Abstract: To investigate if synergism occurs between pyrethroids, organophosphates and new insecticides, we tested representatives of these compounds (bifenthrin, chlorpyrifos, spinosad, indoxacarb and emamectin) against the diamondback moth (Plutella xylostella). Larvicidal activity of these insecticides was assessed separately and together on a susceptible strain (Lab‐UK) of P. xylostella as well as a field population collected from Multan. The field population showed significant resistance to chlorpyrifos (331 100‐fold), bifenthrin (45 200‐fold), emamectin (1800‐fold), spinosad (11‐fold) and indoxacarb (5600‐fold) when compared with the Lab‐UK population. When insecticides were mixed based on LC₅₀ and tested at serial concentrations against Lab‐UK, significant synergy (CI < 1) occurred between bifenthrin, spinosad and emamectin. In contrast, the interaction between bifenthrin and indoxacarb was additive (CI = 1). The toxicity of bifenthrin against the field population increased significantly (P < 0.01) when combined with spinosad, emamectin and indoxacarb. Synergistic effects could be attributed to the complementary modes of action by these insecticide classes acting on different components of nerve impulse transmission (which are not identical for bifenthrin and indoxacarb either). However, chlorpyrifos/bifenthrin mixture was not significantly different either from bifenthrin or chlorpyrifos alone, indicating an additive affect. In combination with spinosad and emamectin, tested against the resistant field population, the toxicity of chlorpyrifos increased significantly and even more so with indoxacarb. Mixtures could also give rise to multiple resistance that may extend across other chemical classes and thus become difficult to manage. Therefore, alternative strategies such as mosaics or rotations should be considered. That is, though synergistic effects have been found, this should not be followed up as a strategy to manage resistant field populations.     

Piperonyl butoxide synergizes the larvicidal activity of Origanum vulgare essential oil and its major constituents against the larvae of Aedes albopictus and Culex pipiens quinquefasciatus

Mosquitoes bite human beings and transmit many diseases, such as malaria, dengue fever, and Zika virus. Vector control of mosquitoes is an effective strategy for reducing the spread of disease. However, extensive use of insecticides (e.g. pyrethroids and organophosphorus) has caused resistance in mosquitoes, which weakens the effectiveness of mosquito control. Phytochemicals have been considered an alternative approach to mosquito control. Essential oil (EO) was obtained from the leaves and flowers of Origanum vulgare, and its synergistic activity with piperonyl butoxide (PBO) was tested against Aedes albopictus and Culex pipiens quinquefasciatus larvae. Thirty-seven compounds were identified, among which carvacrol and thymol were two major constituents (30.73 % and 18.81 %, respectively). O. vulgare EO had a significant toxic effect against fourth-stage larvae of Cx. p. quinquefasciatus and Ae. albopictus, with LC₅₀ values of 17.51 and 75.90 mg/L. Carvacrol and thymol also each appeared to be more effective against Cx. p. quinquefasciatus (LC₅₀ = 19.30 and 11.56 mg/L, respectively) than Ae. albopictus (LC₅₀ = 26.62 and 26.66 mg/L, respectively). PBO interacted synergistically with O. vulgare EO, carvacrol and thymol with 2.60–6.26 times as much of the active compound needed without PBO as against Cx. p. quinquefasciatus and Ae. albopictus larvae. Overall, our results contribute to the development of new natural mosquito insecticides.     

The influence of ecological factors on mosquito abundance and occurrence in Galápagos

We sampled mosquitoes across 18 sites established at different elevations and stretching from the north to the south of Isla Santa Cruz, Galápagos. Two commonly occurring species, Ae. taeniorhynchus and Cx. quinquefasciatus, were collected along with environmental variables characteristic of the trapping sites to assess their influence on mosquito abundance and occurrence in the dry season of 2015. We captured Ae. taeniorhynchus at 14 out of 18 sites and Cx. quinquefasciatus at low and high elevation sites on Santa Cruz. We utilized two generalized linear models; the first assessed the influence of environmental variables on abundances of Ae. taeniorhynchus and the second assessed the influence of these variables on the presence of Cx. quinquefasciatus. Populations of both mosquito species declined with elevation. Rainfall data were limited, as we sampled during the dry season of 2015. Distance to mangroves and maximum humidity were significant in influencing the abundance of Ae. taeniorhynchus, while maximum humidity was found to significantly influence the presence of Cx. quinquefasciatus. Both species occurred in sites where temperature, precipitation, and humidity should allow for mosquito development as well as parasitic development of the protozoan parasites that cause avian malaria. Further research involving year‐round sampling of mosquitoes and accompanying meteorological data as well as experimental studies on vector competence are required to understand disease dynamics of parasites such as avian malaria in Galápagos.     

Insecticide susceptibility and resistance of Culex tritaeniorhynchus (Diptera: Culicidae) larvae collected from Gwangju,Republic of Korea

The susceptibility of Culex tritaeniorhynchus collected from Gwangju, Jeollabuk Province, Republic of Korea (ROK) to insecticides was evaluated under laboratory conditions using ten insecticides (7 pyrethroids and 3 organophosphates) that are currently applied by local public health centers in the ROK. Based on the values of median lethal concentration (LC₅₀), Cx. tritaeniorhynchus larvae were most susceptible to chlorpyrifos (0.006 ppm), fenitrothion (0.022 ppm), fenthion (0.035 ppm) and bifenthrin (0.038 ppm), and were least susceptible to esbiol (1.722 ppm). In comparative resistance tests, the resistance ratios (RRs) of seven insecticides were compared among each other using two strains of Cx. tritaeniorhynchus that were collected from the same locality during 1992 and 2010. Culex tritaeniorhynchus demonstrated significantly increased RRs to pyrethroids over time, while demonstrating decreased RRs among the organophosphates. Among the pyrethroids, permethrin had the highest RR values of 182.1‐ and 833.3‐fold differences, followed by etofenprox with RRs of 138.4‐ and 224.1‐fold differences in values of LC₅₀ and concentration that produced 90% mortality (LC₉₀), respectively. Culex tritaeniorhynchus strains demonstrated the least amount of change in susceptibility to the organophosphates, chlorpyrifos, fenitrothion and fenthion with 0.020‐, 0.019‐ and 0.001‐fold differences in resistance ratios (RRLC₅₀), respectively.     

Oviposition preference and offspring performance in container breeding mosquitoes: evaluating the effects of organic compounds and laboratory colonisation

1. The preference–performance hypothesis (PPH) predicts that organisms lacking parental care should oviposit in habitats that optimise offspring performance. Preference–performance relationships were investigated for the Asian tiger mosquito (Aedes albopictus Skuse) and the southern house mosquito (Culex quinquefasciatus Say) (Diptera: Culicidae), two medically important container‐breeding species, in response to an organic chemical blend mimicking decaying plant matter. Additionally, the effects of long‐term laboratory colonisation of Cx. quinquefasciatus using wild and laboratory strains were evaluated. 2. Oviposition bioassays were conducted by releasing gravid mosquitoes into field enclosures with automobile tires containing low and high concentrations of the chemical blend, and water controls. The offspring were then reared in water collected from the tires in which they were deposited. 3. Aedes albopictus and wild Cx. quinquefasciatus laid more eggs in the chemical blend than water controls but did not differentiate between the low and high concentrations. Conversely, laboratory Cx. quinquefasciatus only preferred the high concentration to the low concentration. No statistical associations between oviposition preference and larval survival were found, as the chemical blend did not affect survivorship of either species. 4. The oviposition preference for the chemical blend over water controls suggests that both species oviposit in the best available resource environment, but further studies are needed before conclusions regarding preference–performance relationships can be drawn. 5. It was found that long‐term laboratory colonisation affects the oviposition behaviour in Cx. quinquefasciatus, suggesting that behavioural studies on laboratory strains are not always applicable to wild populations.     

Laboratory evaluation of lactic acid on attraction of Culex spp. (Diptera: Culicidae)

The role of lactic acid was evaluated for attraction of Culex nigripalpus, Culex quinquefasciatus, Culex tarsalis, and Aedes aegypti in the laboratory using a dual‐port olfactometer. When lactic acid was combined with chicken odor, attraction was increased for Cx. quinquefasciatus compared to chicken odor alone but not for Cx. nigripalpus, Cx. tarsalis, and Ae. aegypti. Lactic acid combined with hand odor did not change attraction of Cx. tarsalis and Ae. aegypti but decreased attraction of Cx. nigripalpus and Cx. quinquefasciatus. The addition of lactic acid to CO₂ increased attraction of Ae. aegypti and Cx. quinquefasciatus but reduced attraction of Cx. nigripalpus and Cx. tarsalis. Use of commercial lactic acid baits with CO₂ resulted in a similar trend except for Cx. nigripalpus which showed no difference. A blend of lactic acid, acetone, and dimethyl disulfide was attractive to Ae. aegypti (63.4%) but elicited low responses by all Culex spp. (1.3–26.8%). Addition of the blend to CO₂ increased attraction of Ae. aegypti and Cx. quinquefasciatus but reduced attraction of Cx. nigripalpus and Cx. tarsalis. The mixture of compounds plus CO₂ was as attractive as a hand for Cx. quinquefasciatus, Cx. tarsalis, and Ae. aegypti.     

Comparative efficacy of different pesticides against mango bark beetle Hypocryphalus mangiferae Stebbing (Coleoptera: Scolytidae)

Hypocryphalus mangiferae Stebbing is one of the most destructive insect pests of mango trees and is found to be associated with the transmission of causal organisms of mango sudden death disease. The present study was carried out to evaluate the toxicity of deltamethrin, bifenthrin, chlorpyrifos, emamectin benzoate, imidacloprid and spinosad in laboratory and field trials. Bioassay results showed that the toxicity of chlorpyrifos was significantly higher than deltamethrin but similar to bifenthrin. Deltamethrin and bifenthrin toxicity, however, increased significantly (P < 0.01) from day 1 to day 3. Spinosad was the least toxic compound while emamectin was the most toxic among new chemical insecticides tested, but its toxicity increased significantly from day 1 to day 5. Comparison of the efficacies of the insecticides using lethal times to produce 50% mortality (LT₅₀) and 90% mortality (LT₉₀) showed that the relative potencies of chlorpyrifos, emamectin, imidacloprid and spinosad were greater than bifenthrin and deltamethrin. The results of field trials showed the highest number of beetles emerged from the control twigs while significantly fewer beetles emerged from the twigs treated with bifenthrin (P < 0.05), which accounted for 12% for bifenthrin compared to that of the control. The present study demonstrated increased toxicities of systemic insecticides and chlorpyrifos compared to toxicities of deltamethrin and bifenthrin, suggesting these insecticides could be an alternative tool in a comprehensive H. mangiferae management program to eradicate the beetles from mango orchards.     

Blood meal sources of mosquitoes captured in municipal parks in São Paulo,Brazil

The aim of this study was to investigate blood meal sources of mosquitoes captured in municipal parks in the city of São Paulo, Brazil, and to identify possible associations between mosquito species and their food preferences. Fourteen species of blood hosts of 510 engorged adult female mosquitoes were identified using PCR assays with a vertebrate‐specific primer set based on cytochrome b mitochondrial DNA of the following vertebrates: birds, dogs, cats, rodents, humans, and other primates. Mosquitoes were captured using a manual aspirator, CDC traps in the canopy, CDC traps at ground level, and Shannon traps. With the exception of cats, all other vertebrates were used as hosts by mosquitoes in the parks. Statistical analysis failed to show any trend toward association between most culicid species captured and the sources of blood meals. Instead, they revealed random patterns, indicating that the mosquitoes fed on the most abundant or convenient blood meal sources. Although feeding preferences were observed in two species (birds in the case of Cx. nigripalpus and dogs in the case of Cx. quinquefasciatus), our results highlight the opportunistic feeding habits of the female mosquitoes in this study.