culicoides trap comparison in south africa gert venter, karien labuschagne, ina hermanides, daphney...

Culicoides trap comparison in South Africa

Gert Venter, Karien Labuschagne, Ina Hermanides, Daphney Majatladi, Solomon Boikanyo

• 4 traps summer (high abundance)• 4 traps winter (low abundance)• 5 traps spring

Culicoides trap comparison in South Africa

CDCUK

OPRIEB

Name: ONDERSTEPOORTSouth Africa8W, Black light blue 30cm220VRelative robust and heavy4 Kg

Light trap comparisons

Name: RIEB2000-2006 France4W, UV 15cm12VRelative light weight and compact1 Kg + 12V car batteryRelative small collecting jar

Light trap comparisons

Name: Miniature CDCSpain & PortugalBlack light blue 15cm6VCommercially available from the USALight weight small0.8 Kg + 6V battery (2.2 Kg)

Light trap comparisons

Name: PirbrightUnited Kingdom & Europe in the past4W, Incandescent white220VNot available anymore2.4 KgRelative small collecting jar

Light trap comparisons

RIEBOPCDCUK4

OPRIEBUKCDC3

UKCDCOPRIEB2

CDCUKRIEBOP1

4321Day/Site

4321

Day/Site

UKRIEBCDCOP4

RIEBUKOPCDC3

OPCDCRIEBUK2

CDCOPUKRIEB1

OPUKCDCRIEB4

UKRIEBOPCDC3

RIEBCDCUKOP2

CDCOPRIEBUK1

4321Day/Site

Traps were deployed in either 3 replicates of a 4X4 or 2 replicates of a 5X5 randomized Latin square design

The advantage being that treatment means were independent of effects due to sites or occasion and, as only one treatment occupied a site on any occasion trap interaction was avoided

Traps were operated from dusk to dawn under the eves of a stable housing cattle at the ARC-OVI. Nights with trap failure were repeated the following night.

Large collections were sub-sampled and all species were classified according to abdominal pigmentation into: Nulliparous (unpigmented) females Parous (pigmented) females Gravid females Freshly bloodfed females and males

Data were analysed using Genstat. Log transformation was used to stabilize the variance

Material & Methods (Light trap comparisons)

SUMMER643 374 Culicoides in 48 collections(Avg 13 403.6)

Significant differences in the average number of Culicoides collected per night by each of the 4 traps

RESULTS & DISCUSION (Light trap comparisons)

OP63%

OP63%

UK b7%

UK6% CDC a

18%CDC26%

RIEB ab12%

RIEB5%

WINTER4 931 Culicoides in 48 collections(Avg 102.7)

Comparisons were repeated in winter, when Culicoides numbers were low, the Onderstepoort trap still collected more midges. All 4 traps captured Culicoides

RESULTS & DISCUSION (Light trap comparisons)

OP RIEB CDC UK

Max 97 290 19 152 31 977 12 617

Avg 33 950.9 2 670.1 (7.9%)

13 732.8(40.4%)

3 260.8(9.6%)

MinNon Cul : Cul

2 4841:11

1741:7

7911:6

901:5

% C. imicola% C. enderleini

95.0 a4.5 a

91.87.6

94.3 b5.4 b

94.5 ab4.6 ab

No of species 12 12 7 13

Unique C. expectator (183)C. schultzei (92)C. nivosus (5)

C. brucei (48) C. nevilli (12)C. similis (4)C. gulbenkiani (3)

Summer: 8-26 January 2008,18 different Culicoides species were collected

Trap

RESULTS & DISCUSION (Light trap comparisons)

OP RIEB CDC UK

Max 680 213 191 103

Avg 256.5 49.9 (19.5%) ab 73.9 (28.8) a 30.5 (11.9) b

MinNon Cul : Cul

61:11 a

31:10 a

11:5

11:2

% C. imicola% C. bolitinos

95.0 a2.1 b

94.5 a3.0 b

94.8 a2.5 b

92.9 a2.5 b

No of species 8 5 7 5

Unique C. pycnostictus

Reduction from summer

132.6 a 53.5 185.8 106.9 a

Winter: 18 July – 8 August 2008, 8 different Culicoides species were collected

Trap

Name: BG-Sentinel MosquitoDesign for the collection of mosquitoesBlack light blue220V/12VLight weight, compact, collapsible1.4 Kgmidges do not go through the fan

Light trap comparisons

CDC26% a

OP51%

RIEB4% b

UK3% b

BG16% a

2 repeats of a 5X5 Latin square: 14-27 August 2008 31 358 Culicoides in 50 collections (Avg 627.2)

RESULTS & DISCUSION (Light trap comparisons)

OP RIEB CDC UK BG-Sentinel

Max 2 820 440 2 524 313 879

Avg 1 597.9 (1) 134 (8.4%) 807.4 (50.5%)

85.1 (5.3%) 511.4 (32.0%)

MinNon Cul : Cul

4571:12

151:8

1481:10

11:1 a

2231:1 a

%C. imicolaC. bolitinosC. nevilliC. magnus

97.5 a0.6 a0.6 a0.5 a

97.4 a0.7 ab0.6 ab0.4 a

98.0 a0.2

0.7 abc0.4 a

93.41.2 ab

2.21.6

97.4 a0.5 ab0.9 bc0.4 a

No of species

13C. bedfordi (1)

6 10 10 12C. neavei (1)

RESULTS & DISCUSION (Light trap comparisons)

Five traps, 50 collections, total of 14 species

• As transovarial transmission of orbiviruses are not known to occur in Culicoides the number of parous individuals is of importance in determining the potential vector status of a specific population. I.e. only parous females are considered as being infected

• All traps indicated that males, freshly bloodfed and gravid females,

especially of C. imicola, were less attracted to light traps than parous and nulliparous females

• This was not true for C. exspectator, C. leucostictus C. nigripennis grp, C. pycnostictus, C. tropicalis and C. nivosus where gravid females and males, singly or when combined, predominated in all 4 traps

RESULTS & DISCUSSION (Light trap comparisons)

Parous rates in C. imicola as determined by the four traps

%Nulliparous %parousOnderstepoort 54.5%a 39.9% aCDC 52.8% b 41.5% bUK 40.6% 48.1%RIEB 55.9% ab 41.0% ab

RESULTS & DISCUSSION (Light trap comparisons)

0

10000

20000

OP RIEB CDC UK

C. imicola nulliparous C. imicola parous

0

10000

20000

30000

OP RIEB CDC UK

Nu

mb

er

co

llecte

d

Avg C. imicola Avg males

The relative abundance of males in collections may indicate nearby breeding sites and the collection of males in winter may indicate continuous breeding Abundance of male C. imicola and C. enderleini as determined by the four traps

%MalesC. imicola C. enderleini

Onderstepoort 5.1% a 17.6% CDC 5.1% a 19.8%aUK 8.1% 18.1%RIEB 1.4% 12.8%a

RESULTS & DISCUSSION (Light trap comparisons)

DISCUSSION / CONCLUSIONS (Light trap comparisons)

• The Onderstepoort trap will increase monitoring sensitivity where vector abundances are low and it will collect more live midges for vector competence and other laboratory studies

• It must be taken into consideration that when a light trap is placed in the immediate vicinity of animals, it intercepts only a portion of the active blood seeking females. The exact size of this portion is not known but is deemed to be <0.0001%

• Light traps do not attract male and/or blood fed and gravid females• To facilitate comparison of data and data sharing, standard techniques for

measuring the variables of vectorial capacity should be developed and adopted

• Despite the a great variety of factors that can influence the numbers of Culicoides midges collected with light traps it is still the most practical way to determine vector abundance

• It will be essential that biases in trapping methods be measured and that trapping methods be evaluated against each other

• Thank you