Fine-scale spatial and temporal variations in insecticide resistance in Culex pipiens complex mosquitoes in rural south-eastern Tanzania

Table 4 Mean % mortality recorded 24 hours after exposure to lambda-cyhalothrin and deltamethrin, with and without synergist, TPP (triphenyl phosphate) or PBO (piperonyl butoxide). The mosquitoes tested were 3- to 5-day-old adult Culex mosquitoes reared from wild-collected larvae from Minepa and Mavimba wards in Ulanga District, Tanzania, in 2015 and 2016

Treatment	No. of replicates	Sample size	Mean % mortality (95% CI)
			Mavimba (8.312°S, 36.677°E)		Minepa (8.271°S, 36.677°E)
			0.05% deltamethrin	0.05% lambda-cyhalothrin	0.05% deltamethrin	0.05% lambda-cyhalothrin
Tests with triphenyl phosphate (TPP)
Environmental control	4	80	0	1.3 (-2.7–5.2)	0	0
Solvent control	4	80	0	0	0	0
20% TPP only	4	80	0	1.3 (-2.7–5.2)	0	0
20% TPP and test insecticide	4	80	86.0 (77.8–94.2)^a	83.8 (76.1–91.4)^a	81.3 (63.6–98.9)^a	73.8 (48.3–99.2)^a
Test insecticide only	4	80	75.0 (68.9–81.1)^b	72.5 (62.2–82.8)^b	51.3 (23.7–79.8)^b	71.3 (47.5–95.2)^a
Tests with piperonyl butoxide (PBO)
Environmental control	4	80	0	0	0	0
Solvent control	4	80	0	1.3 (-2.7–5.2)	0	0
4% PBO only	4	80	0	1.3 (-2.7–5.2)	0	0
4% PBO and test Insecticide	4	80	60.0 (42.8–77.2)^a	66.3 (54.3–78.2)^a	93.8 (86.1–101.4)^a	57.5 (32.8–82.2)^a
Test insecticide only	4	80	41.3 (33.6–48.9)^b	28.8 (15.2–42.3)^b	73.8 (53.9–93.6)^b	35.0 (20.5–49.5)^b

Notes: Morphological identification of the Culex mosquito populations revealed 94% were Cx. pipiens complex. Of these, PCR assays revealed that 81% were Cx. quinquefasciatus, 2% were Cx. pipiens pipiens and 3% were hybrids of the two species. About 14% of the specimens were non-amplified. These test results can therefore be considered primarily representative of Cx. pipiens complex or more specifically for Cx. quinquefasciatus. Environmental control refers to a control where mosquitoes are exposed to non-treated papers, and is used to assess any contamination in the test environment or during the procedures
^a,bThe letters a and b signify statistically significant differences between % mortalities obtained in tests with or without the synergists

ISSN: 1756-3305