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Table 3 Fine-scale spatial and seasonal variations in insecticide susceptibility of Culex mosquitoes collected in three neighbouring wards in the Ulanga District, Tanzania, in the dry season (June–December 2015) and wet season (January–May 2016). Adult mosquitoes exposed for each insecticide were either 20 or 25 per replicate. Results expressed as % mean mortality 24 hours post-exposure

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

 

Insecticide

Minepa (8.271°S, 36.677°E)

Mavimba (8.312°S, 36.677°E)

Lupiro (8.385º S, 36.670º E)

Dry season

Wet season

Dry season

Wet season

Dry season

Wet season

Female mosquitoes

0.75% permethrina,b

100SS

100SS

100SS

100SS

100SS c

72.0RR c

0.05% deltamethrin

86.0RR c

56.3RR c

87.0RR

90.0RS

8.0RR c

87.5RR c

0.05% lambda-cyhalothrin

60.0RR

82.5RR

76.3RR c

91.3RS c

80.0RR c

87.5RR c

4% dieldrin

94.0RS

98.8SS

98.8SS

100SS

100SS

100SS

4% DDT

92.0RS

95.0RS

87.5RR

91.3RS

78.0RR

71.0RR

0.1% propoxur

94.0RS

100 SS

91.3RS c

100SS

100SS

98.0SS

0.1% bendiocarba,b

29.0RR c

99.0SS c

98.0SS

100SS c

100SS

99.0SS

0.25% pirimiphos-methyl

100SS

100SS

90.0RS c

100SS c

100SS

100SS

5% malathion

100SS

100SS

100SS

97.5SS

99.0SS

100SS

Control (untreated paper)

4.6

2.4

2.2

1.8

1.2

2.9

Male mosquitoes

0.75% permethrin

100SS

100SS

98.8SS

100SS

100SS

100SS

0.05% deltamethrinb

90.0RS

93.0RS

97.5RS

98.8SS

99.0SS

95.0RS

0.05% lambda-cyhalothrina,b

88.0RR c

99.0SS c

100SS

98.8SS

71.0RR

92.0RS

4% dieldrin

100SS

100SS

100SS

100SS

100SS

100SS

4% DDTa,b

97.0RS

95.0RS

77.0RR

98.8SS

99.0SS

100SS

0.1% propoxur

93.0RS

99.0SS

97.0RS

100SS

100SS

100SS

0.1% bendiocarba,b

58.0RR c

100SS c

100SS

98.0SS

100SS

100SS

0.25 % pirimiphos-methyl

100SS

98.0SS

97.0RS

100SS

100SS

100SS

5% malathion

100SS

100SS

100SS

100SS

100SS

100SS

Control (untreated paper)

1.1

11.2

4.8

2.5

2.6

3.9

  1. Notes: Morphological identification of the Culex mosquitoes 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
  2. Abbreviations: SS, mosquitoes were susceptible to the test insecticide (WHO assays mortality between (98% and 100%); RS, mosquitoes had reduced susceptibility indicating possible resistance and need for further investigation (mortality of 90–97%); RR, mosquitoes were confirmed resistant to the test insecticide (WHO assays mortality below 90%)
  3. aChemicals for which we observed differences in susceptibility of Culex mosquitoes between dry and wet seasons, i.e. where mosquitoes were fully susceptible in one season and fully resistant in a different season in same ward
  4. bChemicals for which we observed differences in susceptibility of Culex mosquitoes between (nearby) wards, i.e. where mosquitoes were fully susceptible in one ward and fully resistant in another ward during the same season
  5. cThere was a statistically significant difference in mortality between the dry and wet seasons