Species composition and feeding pattern of malaria vectors in indoor and non-indoor residual spraying districts of Lira and Kole, Northern Uganda

Background Vector control interventions using long-lasting insecticidal nets and indoor residual spraying are common tools deployed for the control of malaria in Uganda. To evaluate the effectiveness of these control tools and understand the prevailing malaria vectors, a study was conducted to determine the species composition, indoor resting population density, and biting pattern of malaria vectors in Indoor Residual Spraying and non-Indoor Residual Spraying districts of Lira and Kole, Northern Uganda. Methods Both indoor and outdoor adult malaria vectors were collected from August to September 2022 using Human-Baited Catch and Pyrethrum Spray Catch methods. To identify the different sibling species of An. gambiae and An. funestus complexes, mosquitoes were identified morphologically and using Polymerase Chain Reaction. Results The non-Indoor Residual Spraying district of Kole had a relatively high density of vectors (67.5%) compared with the Indoor Residual Spraying district of Lira (32.5%). An. gambiae s.s. dominated the composition of the vectors (43.1%)) in the non-IRS district, followed by An. funestus (30.4%) and An. arabiensis (26.5%). In the IRS district, An. funestus was the predominant species (52.3%), followed by An. gambiae s.s. (34.1%) and An. arabiensis (13.61%). Although Kole district had a slightly higher Indoor Resting Density (IRD) than Lira district, there was no statistically significant difference between the IRD in the two districts. In IRS district, An. funestus and An. gambiae s.s. had an indoor biting peak of 3:00–4:00AM and outdoors from 21:00–1:00 AM. Conclusion There was no statistically significant difference in either the indoor or outdoor biting rates of all malaria vectors in the two districts. This indicates that the population could be protected while resting indoors, as the peaks observed during the night correspond to moments when the population is asleep, unlike the peak that occurs during the morning when people are awake and remain unprotected by Long Lasting Insecticides Nets. The high numbers of An. gambiae in the non-IRS district and An. funestus in the IRS district indicates a high malaria transmission potential and predicts the risk of a malaria upsurge within the study area. An. arabiensis was predominant in the unsprayed district compared to that in the sprayed district.