Mosquito oviposition site selection is essential for vector population dynamics and malaria epidemiology. Irrigated rice cultivations provide ideal larval habitats for malaria mosquitoes, which has resulted in increased prevalence of the malaria vector, Anopheles arabiensis, in sub-Saharan Africa. The nature and origin of the cues regulating this behaviour are only now being elucidated. We show that gravid Anopheles arabiensis are attracted and oviposit in response to the odour present in the air surrounding rice. Furthermore, we identify a synthetic rice odour blend, using electrophysiological and chemical analyses, which elicits attraction and oviposition in laboratory assays, as well as attraction of free-flying gravid mosquitoes under semi-field conditions. This research highlights the intimate link between malaria vectors and agriculture. The identified volatile cues provide important substrates for the development of novel and cost-effective control measures that target female malaria mosquitoes, irrespective of indoor or outdoor feeding and resting patterns.

BackgroundDevelopment strategies in Ethiopia have largely focused on the expansion of irrigated agriculture in the last decade to reduce poverty and promote economic growth. However, such irrigation schemes can worsen the socio-economic state by aggravating the problem of mosquito-borne diseases. In this study, the effect of agro-ecosystem practices on malaria prevalence and the risk of malaria transmission by the primary vector mosquito, Anopheles arabiensis, in Ethiopia were investigated.MethodsIn three villages in western Ethiopia practising large-scale sugarcane irrigation, traditional smallholder irrigation and non-irrigated farming, cross-sectional parasitological surveys were conducted during the short rains, after the long rains and during the dry season. Entomological surveys were undertaken monthly (February 2010-January 2011) in each village using light traps, pyrethrum spray collections and artificial pit shelters.ResultsMalaria prevalence and the risk of transmission by An. arabiensis assessed by the average human biting rate, mean sporozoite rate and estimated annual entomological inoculation rate were significantly higher in the irrigated sugarcane agro-ecosystem compared to the traditionally irrigated and non-irrigated agro-ecosystems. The average human biting rate was significantly elevated by two-fold, while the mean sporozoite rate was 2.5-fold higher, and the annual entomological inoculation rate was 4.6 to 5.7-fold higher in the irrigated sugarcane compared to the traditional and non-irrigated agro-ecosystems. Active irrigation clearly affected malaria prevalence by increasing the abundance of host seeking Anopheles mosquitoes year-round and thus increasing the risk of infective bites. The year-round presence of sporozoite-infected vectors due to irrigation practices was found to strengthen the coupling between rainfall and risk of malaria transmission, both on- and off-season.ConclusionThis study demonstrates the negative impact of large-scale irrigation expansion on malaria transmission by increasing the abundance of mosquito vectors and indicates the need for effective vector monitoring and control strategies in the implementation of irrigation projects.

BackgroundMaize cultivation contributes to the prevalence of malaria mosquitoes and exacerbates malaria transmission in sub-Saharan Africa. The pollen from maize serves as an important larval food source for Anopheles mosquitoes, and females that are able to detect breeding sites where maize pollen is abundant may provide their offspring with selective advantages. Anopheles mosquitoes are hypothesized to locate, discriminate among, and select such sites using olfactory cues, and that synthetic volatile blends can mimic these olfactory-guided behaviours.MethodsTwo-port olfactometer and two-choice oviposition assays were used to assess the attraction and oviposition preference of gravid Anopheles arabiensis to the headspace of the pollen from two maize cultivars (BH-660 and ZM-521). Bioactive compounds were identified using combined gas chromatography and electroantennographic detection from the headspace of the cultivar found to be most attractive (BH-660). Synthetic blends of the volatile compounds were then assessed for attraction and oviposition preference of gravid An. arabiensis, as above.ResultsHere the collected headspace volatiles from the pollen of two maize cultivars was shown to differentially attract and stimulate oviposition in gravid An. arabiensis. Furthermore, a five-component synthetic maize pollen odour blend was identified, which elicited the full oviposition behavioural repertoire of the gravid mosquitoes.ConclusionsThe cues identified from maize pollen provide important substrates for the development of novel control measures that modulate gravid female behaviour. Such measures are irrespective of indoor or outdoor feeding and resting patterns, thus providing a much-needed addition to the arsenal of tools that currently target indoor biting mosquitoes.Electronic supplementary materialThe online version of this article (doi:10.1186/s12936-016-1656-0) contains supplementary material, which is available to authorized users.

The coffee berry borer, Hypothenemus hampei is a serious pest in many coffee growing countries. Electrophysiological and behavioral responses of H. hampei to volatiles of different phenological stages of coffee, Coffea arabica, fruits were studied in order to identify volatile semiochemicals used in host location. Volatiles were collected from different phenological stages of C. arabica fruit by air entrainment. Electrophysiological recordings were made from insect antennae. Behavioral assays were carried out using a Perspex four-arm olfactometer. Insects spent significantly more time in the region of the olfactometer where ripe and dry fruit volatiles were present compared to control regions. Coupled gas chromatography--electroantennography revealed the presence of six electrophysiologically active compounds in C. arabica volatiles. These were identified by using GC and GC-MS as methylcyclohexane, ethylbenzene, nonane, 1-octen-3-ol, (R)-limonene, and (R)-3-ethyl-4-methylpentanol. In the olfactometer bioassay, H. hampei showed a significant response to 3-ethyl-4-methylpentanol, methylcyclohexane, nonane, ethylbenzene, and a synthetic blend of these four compounds. Attraction to the synthetic blend was comparable to that for the natural sample. The significance of the study is discussed in terms of semiochemical based pest management methods of the coffee berry borer.

Adult Schistocerca gregaria were infected with the entomopathogenic fungus Metarhizium flavoviride and their flying ability and rates of food consumption recorded over the subsequent days to death, which usually took about 6 days. Significant reductions in both flight and feeding occurred, usually by the 3rd day after application of the fungus. The diminished levels of pest activities before death reduces the perceived disadvantage of a relatively slow time to kill of the mycoinsecticide.