Species composition of Phlebotomine sandflies (Diptera: Psychodidae) in Nikshahr county, south-eastern Iran.

Background & objectives: Sandflies are reported as the vectors of different kinds of leishmaniasis to human. There are foci of the disease in Iran. The aim of this study was to determine the fauna and species composition of sandflies to find the probable vectors of leishmaniasis in Nikshahr county, south-east of Iran, where cutaneous leishmaniasis is endemic. Methods: Sandflies were collected by sticky paper traps from 20 collection stations located in plain and mountainous area of Nikshahr county. The sex ratio and relative abundance of different species were also determined. Results: A total of 11,455 sandflies revealed 23 species collected and identified. Phlebotomus alexandri, P. sergenti, P. papatasi, P. salehi, and P. keshishiani were the most important vector species found in this study. Interpretation & conclusion: During this survey 13 species are identified for the first time from Nikshahr county—P. bergeroti, P. eleanorae, P. keshishiani, P. halepensis, S. hodgsoni, S. christophersi, S. mervynae, S. dentata, S. dreyfussi, S. iranica, S. africana, S. grekovi and S. palestinensis, while P. keshishiani is an important vector of visceral leishmaniasis in south of Iran. These data demonstrate five vectors of leishmaniasis are active in the study area.

Application of predictive degree day model for field development of sandfly vectors of visceral leishmaniasis in northwest of Iran.

Background & objectives: Temperature plays a significant role in insect’s development where a rise in temperature, accelerates the insect’s metabolic rates, increases egg production and makes blood feeding more frequent. It also shortens the time period required for the development of pathogens within insects. Visceral leishmaniasis (VL) is one of the most important vector-borne diseases transmitted by different sandfly species. In this study, a phenological model was used to estimate the number of generations, peak activity and temporal variability of sandflies in the main VL foci in northwest Iran. Methods: Development requirements of different life stages of a Phlebotomus papatasi laboratory colony were measured and were subjected to the formula for calculation of accumulated degree day (ADD) for field sandflies using the online soft (UC IPM), using horizontal cut-off method and single triangle model. Sandflies population dynamics was monitored in the field during the seasonal activity in the region and its association with the ADD was tested using SAS software. Results: Populations of sandflies accommodated well with the amount of accumulated degree days (ADD) in the region. During the seasonal activity, a total of 639 ADD were produced which was enough to support one complete life cycle and growth of the next generation up to late larval instar. Larvae of the second generation hibernate through winter and the first adult population appears in the mid to late June of the next year when they receive at least 182 ADD from the beginning of the spring. The highest population density of sandflies was observed in early August, followed by a rapid decrease in early September, with the adult population disappearing completely in late September. This is the first degree day model related to sandflies in the most important VL foci of Iran. Interpretation & conclusion: Further studies in various regions with variable climate are recommended in order to better estimate and understand the development time, population dynamics and activities of the vectors which in turn could be used in proper implementation of effective vector control programmes.

Comparative performance of imagicides on Anopheles stephensi, main malaria vector in a malarious area, southern Iran.

BACKGROUND & OBJECTIVES: Jiroft district has subtropical climate and prone to seasonal malaria transmission with annual parasite index (API) 4.2 per 1000 in 2006. Anopheles stephensi Liston is a dominant malaria vector. The monitoring of insecticide susceptibility and irritability was conducted using discriminative dose as described by WHO. METHODS: The IV instar larvae were collected from different larval breeding places and transported to the temporary insectary, fed with Bemax and then 2-3 days-old emerged and sugar-fed adults were used for susceptibility and irritability tests employing WHO methods and kits to organochlorine (OC) and pyrethroid (PY) insecticides. RESULTS: Mortality rates of field strain of An. stephensi were 91.3 +/- 0.14 and 90 +/- 0.47% to DDT and dieldrin, respectively at one hour exposure time but was susceptible to all pyrethroids tested. The average number of take-offs per min per adult was 2.09 +/- 0.13 for DDT, 0.581 +/- 0.05 for dieldrin, 1.85 +/- 0.08 for permethrin, 1.87 +/- 0.21 for lambda-cyhalothrin, 1.53 +/- 0.13 for cyfluthrin, and 1.23 +/- 0.1 for deltamethrin. INTERPRETATION & CONCLUSION: Currently, deltamethrin is being used for indoor residual spraying against malaria vectors in the endemic areas of Iran. The findings revealed that the main malaria species is susceptible to all pyrethroids including deltamethrin, permethrin, cyfluthrin and lambda-cyhalothrin but was tolerant to DDT and dieldrin. This report and the finding are coincided with results of previous studies carried out during 1957-61 in the same area. Irritability tests to OC and PY insecticides revealed the moderate level of irritability to DDT compared to pyrethroids and dieldrin. Monitoring for possible cross-resistance between OC and PY insecticides should come into consideration for malaria control programme.

Morphological method for sexing anopheline larvae.

BACKGROUND & OBJECTIVES: Most of autocidal control of malaria vectors relies on the rearing and release of large numbers of sterile male into a wild population and it would be crucial to separate the males from females before release. This could result in enormous economic benefits in the mass rearing and raise the efficiency of the field operations. The development of genetic sexing of mosquitoes, enabling the release of males only, but impairing the overall fitness of the released insect has been considered greatly. Here we report on a morphological sexing method for the preferential diagnosis and separation of males in late III and IV instar larvae for the mosquitoes Anopheles stephensi Liston and An. culicifacies s.l. (Diptera: Culicidae), the principal vectors of human malaria in Asia and Indian subcontinent. METHODS: Male mosquitoes are identified by their tube like organ at the 9th abdomen segment which originates from segment parallel to the spiracles. Length and width of this organ is measured as 66.66 +/- 9.5 and 14.3 +/- 1.5 microm respectively. The whole length of the organ is 201.63 +/- 23.4 microm. Two fried eggs in the anterior portion of the segment are apparent in males. The length of tube in female is shorter than the male (almost half of the length--37.95 +/- 4.0 microm), its width is slightly stout and wider than the male (16.72 +/- 1.4 microm). Two fried eggs in the anterior portion of the segment are absent. After separation of live male larvae by those characteristics, they were transferred into the trays and emerged adults were identified to ascertain correct identification of sex. RESULTS: All the larvae with male organs developed into male adults with hairy antennae and club shaped palpi, whereas all the female larvae developed into adult females. INTERPRETATION & CONCLUSION: The sex separation at the larval stage will provide a clue for embryonic origin of sex organs, insecticide selection at the larval stage, sex related genes, male sterility and other measures.

Studies on sandflies in a hyperendemic area of zoonotic cutaneous leishmaniasis in Iran.

Ecological studies on sandflies were conducted in the Borkhar rural district, north of Isfahan in central Iran from March 1991 to March 1992. Sandflies were collected once every ten days from human dwellings and cattlesheds using sticky (oiled) paper traps. A total of 29004 sandflies were collected and seven species were identified. Phlebotomus papatasi predominated (83.8% in bedrooms and stables and 42.6% in rodent burrows) in the area. The average indoor resting density of P. papatasi ranged from 0.6 (October 1991) to 62.8 per 10 traps (August 1991). The average outdoor resting density of this species varied between 0.7-141.2 per 10 traps in November and July respectively in 1991. The activity of sandflies extended from end May to mid November. There were two peaks in the density curve of most species, one in June or July and the second in August or September. A significant positive correlation was observed between rainfall and relative density. Natural leptomonad infection was found in P. papatasi, P. caucasicus and P. ansarii, P. papatasi is the main vector to man, but P. caucasicus, P. mongolensis, P. ansarii and P. papatasi act as vectors among gerbils.