Swarming and mating behavior of male Anopheles arabiensis Patton (Diptera: Culicidae) in an area of the Sterile Insect Technique Project in Dongola, northern Sudan.

The problems facing the conventional mosquito control methods including resistance to insecticides have led to the development of alternative methods such as the Sterile Insect Technique (SIT) to suppress populations of the malaria vector Anopheles arabiensis in northern Sudan. This method entails the release of large numbers of irradiated males to compete against wild conspecifics for mating with virgin females in the field. The swarming and mating behaviors of this species were conducted at two field sites during the period 2009-2012 in Dongola, northern Sudan. Observations were made in the field sites and in a contained semi-field enclosure. In addition, participation of released irradiated-marked males in the swarms of wild mosquito was investigated. Swarms were observed on sunset in the vicinity of larval habitats around irrigation channel and stopped with the onset of the darkness about 21-25 min after the start. Swarms were observed above visual markers such as palm trees, bare ground, and manure. Several couples were observed leaving the swarms in copula in the direction of the sunlight. The majority of copulations were observed within 12-15 min of the start of swarming. Relatively low insemination rates (28%) of females collected from coupling pairs were observed. Irradiated-marked males were observed to join the natural swarms regularly, indicating their probable competitiveness with the other wild males. These findings enhance the feasibility of staging an SIT campaign against malaria vector in Northern State-Sudan.

Impacts of agricultural practices on insecticide resistance in the malaria vector Anopheles arabiensis in Khartoum State, Sudan.

BACKGROUND: Agricultural pesticides may play a profound role in selection of resistance in field populations of mosquito vectors. The objective of this study is to investigate possible links between agricultural pesticide use and development of resistance to insecticides by the major malaria vector Anopheles arabiensis in northern Sudan. METHODOLOGY/PRINCIPAL FINDINGS: Entomological surveys were conducted during two agricultural seasons in six urban and peri-urban sites in Khartoum state. Agro-sociological data were collected from 240 farmers subjected to semi-structured questionnaires based on knowledge attitude and practice (KAP) surveys. Susceptibility status of An. arabiensis (n=6000) was assessed in all sites and during each season using WHO bioassay tests to DDT, deltamethrin, permethrin, Malathion and bendiocarb. KAP analysis revealed that pesticide application was common practice among both urban and peri-urban farmers, with organophosphates and carbamates most commonly used. Selection for resistance is likely to be greater in peri-urban sites where farmers apply pesticide more frequently and are less likely to dispose of surpluses correctly. Though variable among insecticides and seasons, broad-spectrum mortality was slightly, but significantly higher in urban than peri-urban sites and most marked for bendiocarb, to which susceptibility was lowest. Anopheles arabiensis from all sites showed evidence of resistance or suspected resistance, especially pyrethroids. However, low-moderate frequencies of the L1014F kdr allele in all sites, which was very strongly associated with DDT, permethrin and deltamethrin survivorship (OR=6.14-14.67) suggests that resistance could increase rapidly. CONCLUSIONS: Ubiquitous multiple-resistance coupled with presence of a clear mechanism for DDT and pyrethroids (kdr L1014F) in populations of An. arabiensis from Khartoum-Sudan suggests careful insecticide management is essential to prolong efficacy. Our findings are consistent with agricultural insecticide use as a source of selection for resistance and argue for coordination between the integrated vector control program and the Ministry of Agriculture to permit successful implementation of rational resistance management strategies.