The invasive shrub Prosopis juliflora enhances the malaria parasite transmission capacity of Anopheles mosquitoes: a habitat manipulation experiment

Abstract

Background: A neglected aspect of alien invasive plant species is their influence on mosquito vector ecology and malaria transmission. Invasive plants that are highly attractive to Anopheles mosquitoes provide them with sugar that is critical to their survival. The effect on Anopheles mosquito populations was examined through a habitat manipulation experiment that removed the flowering branches of highly attractive Prosopis juliflora from selected villages in Mali, West Africa.

Methods: Nine villages in the Bandiagara district of Mali were selected, six with flowering Prosopis juliflora, and three without. CDC-UV light traps were used to monitor their Anopheles spp. vector populations, and recorded their species composition, population size, age structure, and sugar feeding status. After 8 days, all of the flowering branches were removed from three villages and trap catches were analysed again.

Results: Villages where flowering branches of the invasive shrub Prosopis juliflora were removed experienced a threefold drop in the older more dangerous Anopheles females. Population density dropped by 69.4% and the species composition shifted from being a mix of three species of the Anopheles gambiae complex to one dominated by Anopheles coluzzii. The proportion of sugar fed females dropped from 73 to 15% and males from 77 to 10%.

Conclusions: This study demonstrates how an invasive plant shrub promotes the malaria parasite transmission capacity of African malaria vector mosquitoes. Proper management of invasive plants could potentially reduce mosquito populations and malaria transmission.

Keywords: Anopheles gambiae complex; Invasive plants; Prosopis juliflora, Mali.

Fig. 1

Prosopis juliflora with inflorescences (Left). Prosopis juliflora in a village in the Bandigara District, Mali (Right)

Fig. 2

Mean catches of female (a) and male (b) mosquitoes in the pre- and post-intervention monitoring periods. Asterisk represents significant differences between village groups

Fig. 3

Age structure of Anopheles spp. female populations in villages with and without Prosopis juliflora in the pre- and post-intervention monitoring periods. Asterisk represents significant differences between village groups

Fig. 4

Sugar feeding status of a female and b male Anopheles gambiae in villages with and without Prosopis juliflora in the pre- and post-intervention monitoring periods. Asterisk represents significant differences between village groups

Fig. 5

Species composition in villages with and without Prosopis juliflora in the pre- and post-intervention monitoring periods. Red dashed line indicates inflorescence removal (intervention). Asterisks represent significant differences between pre- and post-intervention population density; P = 0.041 for the difference in Anopheles coluzzii population density and P = 0.045 for the Anopheles gambiae s.s. population