The results of these studies show how An. gambiae s.l. are attracted to many types of fruits/seedpods and flowering plants in the natural environment of Mali. The high variation in their attraction highlights how available fruits/seedpods and flowering plants vary in their overall quality for these malaria vectors. Given the nature of An. gambiae s.l. to seek natural sugar sources for their survival [20, 21], the plant-feeding choices these malaria vectors make are apparently influenced very strongly by the diversity, abundance, and seasonal timing of attractive flowering plants and their products.
The attraction periodicity studies on the most attractive flowering plant provide interesting evidence on the timing of female and male An. gambiae s.l. sugar-feeding in nature. There were no major differences in sugar-feeding periodicity between female and male An. gambiae s.l. Clearly, there were pronounced early evening and early morning peaks of activity. This is likely due to behavioural patterns of mosquito attraction but could also be related to the interactions between mosquito behaviour and the timing of volatile release by plants. Not unexpectedly, the periodicity of sugar-feeding differed from the timing of catches in light traps and the use of human odor as bait. This is the first study of the An. gambiae s.l. sugar-feeding periodicity in Africa.
The methods employed using the glue trap proved highly successful for the African environment. In a very short time, a matter of days, it was possible to identify the variety of fruits/seedpods and flowering plants that were significantly attractive to An. gambiae s.l. The methods employed were simple and yielded rigorous data for determination of preferences in nature. Thus, they can be considered very suitable for other environments in Africa.
In the semi-arid regional sites in Mali, there is typically a rainy season when a high diversity of flowering plants is present and a long dry season when the types and abundance of flowering plant is extremely limited. Therefore, for mosquitoes, there is apparently a great variation in the natural sugar sources that are available during the year. It is worthwhile mentioning that at least some of the identified attractive sugar sources like P. reticulatum, and the fig, F. thonningii, are available through most of the dry season and are often peridomestic. This is similar to the situation in Israel where the sugar-feeding field methods and ATSB approaches were developed [6–10]. A limitation of this study is that field-testing was done only at the end of the malaria transmission season in Mali and did not cover the entire flowering season. Further studies to link plant phenology and mosquito sugar-feeding are necessary to complement the picture of mosquito-plant relations.
These studies provide critical information for using ATSB methods for malaria vector control in Mali. First, the studies of An. gambiae s.l. attraction to fruits identify some of most highly attractive fruits that can be used for making attractive sugar bait solutions that are needed for ATSB bait stations [8, 9] and plant spraying [7, 10, 12]. Some are locally available and abundant, and nearly all residents are familiar with them. The utility of using both guava and honey melons, two of the most attractive fruits, was recently demonstrated in the ATSB field trial in Mali . Second, some of the seedpods identified as attractive (e.g. A. albida, P. reticulatum, T. indica) may serve as a key sugar source for mosquitoes; it appeared that the exudates of the fermenting liquid from the seedpods were particularly attractive. Seedpods that are highly attractive and readily available should be considered further for potential use in ATSB methods. However, the seedpods may not be readily available in the local markets. Third, studies of An. gambiae s.l. attraction to flowering plants identified the most attractive and available species of plants. Such information can serve to guide ATSB spraying on the most attractive plants in and around malaria endemic communities. Fourth, the index of attractiveness was higher for the most attractive flowering plant (i.e., A. macrostachya) than the most attractive fruit (i.e., P. guajava), indicating the nature of the plant-mosquito relation in Mali. This obviously may have longer-term implications for the ATSB approach because the semiochemicals responsible for attractiveness may be identified and chemical baits subsequently developed . Ultimately, there is merit in using chemical baits instead of homemade brews of ATSB solutions. There may also be utility in chemically analyzing repellent plants such as H. suaveolens identified in this study or other repellent plants described from Africa .