Optimization of the feeding rate of Anopheles farauti s.s. colony mosquitoes in direct membrane feeding assays

Lincoln Timinao,Thomas R Burkot,Rebecca Vinit,Louis Schofield,Michelle Katusele,Stephan Karl

doi:10.1186/s13071-021-04842-y

Abstract

BackgroundDirect membrane feeding assays (DMFA) are an important tool to study parasite transmission to mosquitoes. Mosquito feeding rates in these artificial systems require optimization, as there are a number of factors that potentially influence the feeding rates and there are no standardized methods that apply to all anopheline species.MethodsA range of parameters prior to and during direct membrane feeding (DMF) were evaluated for their impact on Anopheles farauti sensu stricto feeding rates, including the starving conditions and duration of starving prior to feeding, membrane type, DMF exposure time, mosquito age, feeding in the light versus the dark, blood volume, mosquito density and temperature of water bath.ResultsThe average successful DMFA feeding rate for An. farauti s.s. colony mosquitoes increased from 50 to 85% when assay parameters were varied. Overnight starvation and Baudruche membrane yielded the highest feeding rates but rates were also affected by blood volume in the feeder and the mosquito density in the feeding cups. Availability of water during the pre-feed starvation period did not significantly impact feeding rates, nor did the exposure duration to blood in membrane feeders, the age of mosquitoes (3, 5 and 7 days post-emergence), feeding in the light versus the dark, or the temperature (34 °C, 38 °C, 42 °C and 46 °C) of the water bath.ConclusionOptimal feeding conditions in An. farauti s.s. DMFA were to offer 50 female mosquitoes in a cup (with a total surface area of ~ 340 cm2 with 1 mosquito/6.8 cm2) that were starved overnight 350–500 µL of blood (collected in heparin-coated Vacutainer tubes) per feeder in feeders with a surface area ~ 5 cm2 (with a maximum capacity of 1.5 mL of blood) via a Baudruche membrane, for at least 10–20 min.Graphical

Highlights

Direct membrane feeding assays (DMFA) are an important tool to study parasite transmission to mosquitoes
Blood feeding rates depend on the experimental conditions under which the DMFAs are conducted, including (i) the duration of starvation before exposure, (ii) the starving conditions, (iii) the type of membrane used, (iv) the amount of time mosquitoes are allowed to feed, (v) the mosquito age, (vi) feeding in the light or in the dark, (vii) the blood volume in the feeder, (viii) the density of mosquitoes attempting to feed and (ix) water bath temperature during DMFA (Fig. 1)
Direct membrane feeding assays Water-jacketed glass membrane feeders were connected in series by rubber hoses to a mini aquarium pump placed inside a 37–38 oC water bath (Fig. 2)

Summary

Introduction

Direct membrane feeding assays (DMFA) are an important tool to study parasite transmission to mosquitoes. The mosquito blood feeding rate, i.e., the proportion of mosquitoes that successfully ingest blood, is an important determinant of overall infection success. The success rate of ingesting blood from a membrane feeder can vary depending on the mosquito species, whether the mosquitoes were collected in the wild [6] or reared in a colony [7], as well as the level of adaptation of the colony. Other parameters which potentially influence blood-feeding rates in DMFA but were not investigated here include the blood meal source [8], the haematocrit level, [9] and phagostimulants such as sodium chloride and sodium bicarbonate for Anopheles species [10]. There is a need to optimize DMFA conditions for each colony mosquito species

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Results

Conclusion