G. TIKUBET, W. DUFFERA, T. CIRCA, S.G.A. LEAK, W. MULATU and T. RICHARDSON
Introduction
Study area
Materials and methods
Results
Discussion
References
Trapping has several promising properties as a method of tsetse control. These include cost effectiveness, low-level technology, absence of environmental hazard and the potential for reducing the fly population. Several studies of the use of odour attractants to increase fly catches have been reported in recent years. For example, Vale and Hall (1985) reported increased catches with acetone and with octenol. As early as 1948, Chorley reported responses to cow urine and- dung and to the odour of hippopotami. Trap design has also received attention. Brightwell et al. (1987) showed increased catches with the Ngu trap compared to the biconical trap (Challier et al., 1977). The present study was carried out to compare the effectiveness of combinations of odour attractants and the Ngu and biconical traps.
The study was carried out in the Ghibe River Valley which is 176 km south-west of Addis Ababa by road. The river valley's slope is gentle and the terrain undulating. Altitude ranges from 1000 to 1100 m.a.s.l. The climate is tropical with a short rainy season from March to April and a main rainy season from late May to October. Mean annual rainfall ranges from 500 to 900 mm. Mean annual maximum and minimum temperatures range from 30°C to 37°C and from 10°C to 15°C, respectively.
The broad-leaved deciduous forest in the Upper Ghibe valley has experienced much less bush clearing and cultivation than the open savanna woodland in the Lower Ghibe. Consequently the fly density is much higher in the Upper Ghibe, which was chosen as the site for these experiments.
Combinations of the two trap designs (biconical and Ngu) and an odour attractant (acetone plus cow urine) were tested using a replicated 3x3 latin square design (Table 1). Biconical traps with three different odour attractants were compared to unbaited biconical traps using a replicated 4x4 latin square design (Table 2). This trial was analyzed, however, as a Youden square (Cochran and Cox, 1957) since virtually no flies were caught during the 0600 to 0900 collection period and thus the data from this period was dropped from further consideration. In a third trial the use of pig urine and acetone as odour attractants was compared using biconical traps in a replicated 4x4 latin square design. For this trial the trapping was carried out on four successive days, the collection period being 0600 to 1800 hours each day.
Table 1. Biconical vs. Ngu experimental design.
|
Trap |
Time of Collection |
||
|
0900-1200 |
1200-1500 |
1500-1800 |
|
|
1 |
A |
B |
C |
|
2 |
B |
C |
A |
|
3 |
C |
A |
B |
|
4 |
A |
C |
B |
|
5 |
C |
B |
A |
|
6 |
B |
A |
C |
A = Unbaited biconical trap.
B = Biconical trap baited with acetone and cow urine.
C = Ngu trap baited with acetone and cow urine.
Table 2. Odour attractants experimental design.
|
Trap |
Time of collection |
|||
|
0600-0900 |
0900-1200 |
1200-1500 |
1500-1800 |
|
|
1 |
A |
B |
C |
D |
|
2 |
B |
C |
D |
A |
|
3 |
C |
D |
A |
B |
|
4 |
D |
A |
B |
C |
|
5 |
D |
A |
B |
C |
|
6 |
A |
B |
C |
D |
|
7 |
B |
C |
D |
A |
|
8 |
C |
D |
A |
B |
A = Biconical trap with acetone plus cow urine.
B = Biconical trap with acetone plus hippo dung.
C = Biconical, trap with acetone plus octenol.
D = Unbaited biconical trap.
In each trial the numbers of flies caught varied widely. For this reason, the data were transformed to a logarithmic scale using the transformation y = ln (x+1) before being analyzed. The detransformed mean number of male and female G. pallidipes caught per trap was calculated for each treatment combination. In addition, an index of increased catch was calculated as the ratio of the detransformed mean to the comparable response for the unbaited biconical trap.
The Ngu trap baited with acetone and cow urine showed significant increases (4.8-fold for male flies and 7.5-fold for female flies) over the unbaited biconical trap (Table 3). The biconical traps baited with cow urine, hippo dung and octenol yielded higher catches (1.3- to 2.6-fold increase for male flies, 1.4- to 4.6 fold for females) than unbaited biconical traps (Table 4). Cow urine, however, was the only one of these attractants that showed a significant increase in most instances. Biconical traps baited with pig urine and acetone showed a significant 2.6-fold increase over unbaited biconical traps (Table 5).
Table 3. Detransformed mean catches of male and female G. pallidipes with biconical and Ngu traps using acetone and cow urine as attractants.
|
Trap/Bait |
Time of collection |
Mean |
Index of Increase |
|||
|
0900-1200 |
1200-1500 |
1500-1800 |
||||
|
A. Males |
||||||
|
|
Bicon (no bait) |
0.55 a |
0.67 a |
1.55 a |
0.88 |
1x |
|
|
Bicon (+acetone+cow urine) |
1.08 a |
1.13 ab |
6.30 b |
2.19 |
2.5x |
|
|
Ngu (+acetone+cow urine) |
2.79 b |
1.60 b |
13.21 c |
4.19 |
4.8x |
|
B. Females |
||||||
|
|
Bicon (No bait) |
1.02 a |
1.45 a |
0.87 a |
1.10 |
1x |
|
|
Bicon (+acetone+ cow urine) |
1.72 a |
4.96 b |
3.94 b |
3.31 |
3.0x |
|
|
Ngu (+acetone+cow urine) |
6.01 b |
7.34 b |
14.35 c |
8.24 |
7.5x |
Treatment and time effects significant (P<0.05).
Treatment in same columns followed by the same letter are not significantly different.
Generally the Ngu trap, cow urine and acetone were more effective at increasing the catch of female than of male flies (Tables 3 and 4). Time of day of collection also affected the index of increase.
Table 4. Detransformed mean catches of male and female G. pallidipes with biconical traps using acetone, cow urine, hippo dung and 1-octen-3-ol as attractants.
|
Bait |
Time of collection |
Mean |
Index of Increase |
|||
|
0900-1200 |
1200-1500 |
1500-1800 |
||||
|
A. Males |
||||||
|
|
No Bait |
0.25 a |
0.68 a |
0.94 b |
0.60 |
1.0x |
|
|
Cow urine |
0.95 b |
0.87 a |
3.47 a |
1.54 |
2.6x |
|
|
Hippo dung |
0.36 a |
0.45 a |
1.88 b |
0.78 |
1.3x |
|
|
Octenol |
0.57 a |
0.50 a |
1.00 b |
0.92 |
1.5x |
|
B. Female |
||||||
|
|
No Bait |
0.30 b |
1.06 b |
0.87 c |
0.71 |
1.0x |
|
|
Cow urine |
2.57 a |
3.28 a |
4.12 a |
3.28 |
4.6x |
|
|
Hippo dung |
0.43 b |
1.03 b |
1.65 bc |
0.97 |
1.4x |
|
|
Octenol |
0.89 b |
1.01 b |
2.31 ab |
1.32 |
1.9x |
Treatment and time effects significant (P<0.05).
Treatments in same columns followed by the same letter are not significantly different.
The trials demonstrated that odour attractants and an improved trap design can significantly increase catches of G. pallidipes in the study area. Increasingly intensive land use in the area is causing increased contact between tsetse flies and human and domestic animal populations. Improved trapping, in conjunction with other control strategies, could prove useful in increasing fly mortality, reducing fly-host contact and thus reducing tsetse challenge.
Table 5. Detransformed mean catches of male and female G pallidipes with biconical traps using acetone and pig urine as attractants.
|
Bait |
Male |
Females |
||
|
Mean |
Index of Increase |
Mean |
Index of Increase |
|
|
No Bait |
4.23 |
1.0x |
3.90 |
1.0x |
|
Acetone |
8.26 |
2.0x |
7.02 |
1.8x |
|
Pig urine |
8.33 |
2.0x |
6.39 |
1.6x |
|
Acetone + Pig urine |
10.98 |
2.6x |
10.02 |
2.6x |
Treatment effects significant (P<0.05).
Brightwell, R., R.D. Dransfield, C. Kyorku, T.K. Golder, S.A. Tarimo and D. Mungai. 1987. A new trap for Glossina pallidipes. Trop Pest Manag. 33 (2): 151-159.
Challier, A., M. Eyraud, A. Lafaye and C. Laveissiere. 1977. Amelioration du rendement du piege biconique pour glossines (Diptera, Glossinidae) par l'emploi d'un cone inferieur bleu. Can. ORSTOM, Ser. Entomol. med. Parasitol., 15: 283-286.
Chorley, T.W. 1948. Glossina pallidipes (Austen) attracted by the scent of cattle-dung and urine (Diptera). Proceed. Roy. Entomol. Soc. London, A. 23: 9-11.
Cochran, W.G. and G.M. Cox. 1957. Experimental Designs, Second edition. New York: John Wiley and Sons.
Vale, G.A. and D.R. Hall. 1985. The use of 1-octen-3-ol, acetone and carbon dioxide to improve baits for tsetse flies, Glossina spp. (Diptera: Glossinidae). Bull. Ent. Res. 75: 219-231.
