Abstract: Background and Objective: The pasture area of the Adamawa Plateau was heavily infested with haematophagous flies. Field trials to suggest an efficient anti-vectoral method to farmers was required. The present field trial aimed at evaluating the efficacy of Deltik® 5% Industrially Incorporated (IIS) and Manually Incorporated (MIS) ZeroFly® screen models together with ZeroFly® Nzi and Biconical traps in biting insect control. Materials and Methods: To realize this study, Biconical and Nzi traps were used to monitor the population of vectorspre and post-screens installation using sites in the DFG cattle paddock and abattoir. The functionality test of screens was carried out by choosing two other sites i.e., the Galim Tick Bath (GTB) as the unscreened site and the Ngaoundere Modern Abattoir (NMA) as the screened site. The pre and post-intervention monitoring activities were carried out in the dry (March) and rainy (April) seasons in 2017. The screen functionality test was carried out in May, 2017. Results: Overall, six families of vectors were identified: Tabanidae, Culicidae, Ceratopogonidae, Muscidae and Simuliidae as well as by-catches. Eleven genera were identified and 21 species were regrouped under them. The overall initial trap apparent density (TADi) of vectors was 21.79 flies/trap and that post-intervention (TADf) was 5.73 flies/trap and day. The overall screen reduction rate was 73.70% and was taxonomic group (family, genus and species) dependent. The IIS reductionrate was 79.20%, while that of MIS was 68.29% with no statistically significant difference (p = 0.06). Conclusion: Thepresence of ZeroFly® screen models and traps in the pasture area of Vina du Sud reduced the biting vectors pressure.
INTRODUCTION
The direct (nuisance) and indirect (disease causing) undesirable effects of biting insects all contributes to host (domestic/wild animals and humans) health deterioration, production loss and large economic losses incurred in control, prevention and treatment1. Based on historic facts, Vina division which was found in the Adamawa plateau was considered as a tsetsefree zone, but little follow up was made to report its current status in terms of tsetse re-infestation2. Today, most animal farms in Vina reports high ticks, Stomoxys, tabanids, Simulium, culicids and ceratopogonids burden in the apparent absence of glossines3. From the current questionnaire reports, most cattle breeders in Vina are aware of the impact of ticks and biting flies on animal health and spray their animals twice-thrice a week in the rainy and once a week in the dry season3. A recent report on bovine trypanosomiasis in Ngaoundere revealed the presence of trypanosomes in theblood of cattle even though the parasitaemia was low (+1 = 102-103 trypanosomes per mL of blood)4. This was strong evidence on the occurrence of the disease in the apparent absence of tsetse flies and the role of mechanical vectors that prevailed in the region such as; tabanids and Stomoxys etc. need to be studied to report their incrimination in trypanosomiasis transmission. In Ngaoundere, the Foot-and-Mouth Disease (FMD) virus RNA was isolated from contaminated anatomical parts of the most common stable fly (S. niger) with infective titres (Ct value far less than 30) during the 2016 FMD outbreak5. The FMD and trypanosomiasis figure in the list of most dangerous infectious diseases of cattle in major cattle breeding regions such as; the Adamawa plateau of Cameroon6.
An insecticide treated live-host served as an important control method for flies7 and occurred to be a method of choice by cattle breeders in Vina division3. However, the more serious problem was that cattle were required to kill many flies, especially when they were acting as re-invasion barrier and could only kill a large number if they were in contact with plenty of such flies8. In addition, flies that visited cattle died afterwards, but not before many or all of them fed so that cattle were still challenged by pathogens9. The upshot was that reliance on a few insecticide-treated cattle alone was unlikely to be satisfactory8.
Odor-baited targets were probably the most suitable baits. An overall 94.9% fly reduction using targets was achieved in Ethiopia9. However, insecticide-treated screens (targets) and traps were used with varying success in different parts of Africa10-12. In the north region of Cameroon, significant reductions in tsetse fly density was reported but this study did not consider the effect of insecticide treated screens on other biting insect-groups13. Therefore, the present investigation focused on the efficacy of ZeroFly® Deltamethrin impregnated blue-black screens (industrially and locally impregnated) odor-baited with Octenol in the control of biting insects in the tsetse free pasture area of Galim in the Adamawa Plateau of Cameroon.
MATERIALS AND METHODS
Description of the study area: The study area consisted of the pasture area of Galim. It was 25 km south of the town of Ngaoundere and 1.5-2 km away from the NMA. Geographically it felt between Latitude 07°11’ N and Longitude 013°34’ E. The area was a mosaic of gallery forest, short Savanna trees and vegetation. The hydrographic network consisted of river Vina and smaller streams. The pasture area around the abattoir was frequently fed upon by cattle from the zoo technique station which was 8 km away. The cattle of the DFG COBE project was kept in a 2 km2 pen but were seldom in contact with the animals from the exterior (semi-intensive husbandry system). The climate was a typical Soudano-Guinean type with two seasons, rainy (April-November) and dry (December to March). The cattle paddock of the DFG-COBE project was used because the pasture area had not experienced any fly-control using insecticides since the year 2010. The NMA was another site because cattle of the zoo technique station grazed in this site throughout the year. Tick bath was also used because animals in the area also frequent there to drink water and was site where insecticide spray activities against ticks took place.
Insecticide coated screens: Two ZeroFly® screen models wereused and included Deltik® 5% Manually Impregnated Screen (MIS, n = 5) (120×97 cm) and Deltamethrin 5% Industrially Impregnated Screens (IIS, n = 5) (220×80 cm). The industrially impregnated screen had a phthalogen blue color while the manually impregnated counterpart had a deepblue color. Both screens were made of blue-black polyester cotton material (Fig. 1a, b). Only the IIS was purchased from Vestergaard Frandsen Ltd., Lausanne (VF) and the MIS was locally impregnated in the field with the dilution of the insecticide (Deltik® 5%) made following manufacturer’s instructions. The screens were odor-baited with Octenol that was put in small vials and attached to it. The insecticide used for the manual impregnation was purchased from CAPHAVET in Ngaoundere.
Preparation of MIS screens: The incorporation of the IIS with Deltamethrin 5% was carried out by Vestergaard Frandsen Ltd.,Lausanne (VF), while the MIS was prepared directly in the field.
| Fig. 1(a-b): | Screen models (a) Industrially impregnated screen and (b) Manually Impregnated screens |
Source: Sevidzem et al.3 |
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Preparation of the MIS consisted of incorporating the blue-black clothing with deltamethrin 5% (w/v) suspension concentrate (S.C.) where the commercially available product was diluted with water to a concentration of 0.4% spray liquid.The dilution was made following manufacturer’s instructions briefly; 10 mL of the product was diluted in 10 L of water. Theblue-black clothing was immersed in the deltamethrin solution for 30 min to allow sufficient absorption of the insecticide liquid (an approximated 100 mg active ingredient). Replenishment of manually impregnated screens were two times per week during the rainy season (April) and one time per week during the dry season (March).
Traps: ZeroFly® traps (odor-baited with Octenol) such as Nzi (n = 6) and Biconical (n = 4) with fine mosquito-net cages to permit the capture of other biting insect vectors like mosquitoes, Ceratopogonids and Simulium were used. The ZeroFly® traps were industrially impregnated with Deltamethrin by Vestergaard Frandsen Ltd., Lausanne (VF).
Experimental phases
| • | Pre-intervention phase: The pre-intervention phase constituted of fly-trapping toassess the fly types and abundance before the interventionphase. One trap of each kind was pitched in eachsite (open savanna grass in plateau of paddock, along theriver Vina, gallery forest and abattoir). The distance between micro-environments was between 350 m-1.7 km andthat between trap-types was 200 m and fly collection wasdone after 12 h. Thedisposition of flies in the prospection sites can be seen in Fig. 2. The duration of the pre-intervention phase was 28 days i.e., in the dry season (first two weeks of March, n = 14 days) and in the rainy season (first two weeks of April, n = 14 days) |
| • | Intervention phase: Insecticide-impregnated and odor-baited (Octenol) screens were pitched in all intervention sites (Fig. 2). The screens were set at 100 m from the traps. The presence of ZeroFly® traps in the control unit was to monitor the biting insect-vector abundance. This exercise was carried out in the dry season (last two weeks of March, n = 14 days) and rainy season (last week of April to first week of May, n = 14 days) |
| • | Test for the functionality of screen models: The hypothesis that ZeroFly® screens and traps might be reducing biting insect vector numbers was verified in this section. This activity was carried out during the last two weeks of the month of May, 2017. The test unit consisted of a MIS and IIS screens monitored by a ZeroFly® Nzi trap pitched at the Galim Tick Bath (GTB) while the control consisted of a Nzi trap and no screens, pitched around the Ngaoundere Modern Abattoir (NMA) (Fig. 2). The distance between the test area and the control site was 3 km. The distance between the tick bath and the DFG cattle corral was 2 km |
Fly identification: Fly identification was carried out at the Programme Onchocercoses field station laboratory using morphological keys.
| Fig. 2: | Map of Galim showing the sampled sites |
NMA: Ngaoundere modern abattoir, GTB: Galim tick bath, Source: Sevidzem et al.11 |
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The key of Oldroyd14 for tabanids and that of Zumpt15 for Stomoxys. For culicids, characteristic identification key for Anophelinae species16 and Culicinae17 were used. Simuliidae were identified using the key of Freeman and De Meillon18. The identification of Culicoides was made following the morphological key19.
Statistical analyses: The R (version 3.4.0) and JASP 0.8.5.1 statistical softwares were used for statistical analyses. Data on the apparent densities of the species of biting insect vectors was tested for normality using the Kolmogorov-Smirnov test. The Kruskal Wallis test was used to compare the number of each species caught by traps pitched in the screened and unscreened site as well as in those beside the two screen models. The Wilcoxon signed rank test with continuity corrections was used to compare catches from traps around the two screen models as well as compare their (screens) reduction rates. The Wilcoxon signed-rank test was used to compare catches in the screened and unscreened sites.
Abundance of each fly before and after intervention was defined as the apparent density which was simply the number of insect vectors caught per trap and day and this quantitative parameter was used to calculate the percentage fly reduction rate as shown in the following equation:
Where:
| NFC | = | Number of flies captured |
| NTs | = | Number of traps |
| TDs | = | Number of trapping days |
Where:
| TADi | = | Initial apparent density of fly-type before the deployment of screens |
| TADf | = | Final apparent density following the deployment of screens |
RESULTS
Fly-species composition in the sampled area: The by-catches identified in this study were mainly hymenopterans and non-biting muscids. Six families were identified during the study not ably Muscidae, Tabanidae, Culicidae, Simuliidae and Ceratopogonidae as well as by-catches. The family Muscidae was represented by 7 species and Stomoxys niger niger (72.81%) was the most frequent species (Table 1).The family Tabanidae was represented by 9 different species with Tabanus par (35.94%) being the most frequent (Table 1). Members of the family Culicidae were represented by two genera i.e., Culex and Anopheles with Culex as the most frequent group (Table 1). The family Simuliidae was genus Culicoides (Table 1).
Reduction rates of deltamethrin incorporated zerofly® screens: The screen reduction effect differed with insect group. The overall screen insect vector reducation was 73.70% (Table 2). The highest reduction in trap apparent density was observed with horn flies or Haematobia (100%) followed by biting midges or Culicoides (93.3%). The lowest reduction effect was noticed in culicids (22.60%). The details on the reduction effect of screens on insect vector trap apparent density can be seen in Table 2.
Reduction rate of insect vector population by the two screen models: The reduction rate of the IIS was 79.20% and that of the MIS was 68.29% (Fig. 3). Based on the Wilcoxon rank sum test with continuity corrections, there was no statistical significant difference (p = 0.06206) in the percentage reduction of the two screen models.
Effect of ZeroFly® screen models at species level: Tabanid population was tremendously reduced in traps pitched beside IIS as compared to their MIS counterpart (Fig. 4a). Only T. par did not record a statistically significant difference (p>0.05) in the collections from traps set beside the two screen models (Fig. 4a). For Stomoxyinae, the frequency of S. n. niger remained indifferent in the traps set around the two screen models (Fig. 4b). It was noticed that Haematobia was not caught by traps set beside the two screen models (Fig. 4b). Simulium was rare with zero catches recorded by traps around the MIS (Fig. 4c). The individuals of the genus Culicoides were not caught by traps pitched beside the two screen models (Fig. 4c).There was no Culex caught by traps set beside the MIS (Fig. 4d).
Test for the functionality of the Zerofly® screen models: In total, 135 flies were caught and 80% were from traps in thenon-treated (108) area and only 20% were recorded inthescreened (27) area (Fig. 5). Applying the Wilcoxon signed-rank test, there was a statistical significant difference (p = 0.029) with catches in the screened and unscreened sites during the trial.
| Table 1: | Species composition of biting insect-vectors |
| Table 2: | Reduction rate of insect vectors by insecticide incorporated screens |
TADi: Initial trap apparent density, TADf: Final trap apparent density | |
| Fig. 3: | Insect vector density reduction rate with respect to screen model |
IIS: Industrially impregnated screen and MIS: Manually impregnated screens |
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The species of tabanids identified were frequent in the screened area as compared to the unscreened site (Fig. 6a). Tabanus biguttatus was the only tabanid species that was absent in the two trial sites (Fig. 6a).
| Fig. 4(a-d): | (a) Proportion of tabanids, (b) Muscidae, (c) Simulium/Culicoides and (d) Culicids in relation to screen models |
IIS: Industrially impregnated screen, MIS: Manually impregnated screens |
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| Fig. 5: | Number of haematophagous dipterous insects caught in unscreened and screened sites |
Stomoxys n. niger showed a statistically significant difference (p<0.05) in collections from traps set in the screened and unscreened sites. S. xanthomelas and S. inornatus were the two Stomoxys species absent in the two trial sites (Fig. 6b). Simulium damnosum and Culicoides sp. were absent in screened site (Fig. 6c). A scanty collection of culicids was noticed and both Anopheles and Culex were absent in collections from traps (Fig. 6d).
DISCUSSION
The survey led to the identification of insect vectors of medical and veterinary importance. By-catches were mostly made up of hymenopterans and non-biting muscids were abundant in the present collection. The abundant nature of hymenopterans in field collections has already been reported and could be due to their high resilience and adaptability to conditions of several environments20. The probable reason for the low catches of Ceratopogonidae, Culicidae and Simuliidae can be related to trap-type21 as well as their placement22. Because of this, recent modification of insect traps has been made for the purpose of survey and control of each targeted insect-group21. For tabanids and muscids, Nzi and Vavoua have been shown to be efficient so their high mean apparent densities were not a surprise5,23,24. High collections of Culex as compared to Anopheles were noticed and this observation was like that of already published reports25,26. This observation was not surprising because the study site harbored river Vina and swamps which served as breeding sites for culicids27. Simulium damnosum s.l. was caught and their presence was not surprising too because the river Vina was a well-studied breeding site for the S. damnosum s.l. in the Adamawa plateau of Cameroon27. The presence of ceratopogonids could be related to the abundance of marshy land in the prospected sites that favored their development28.
The occurrence of insect vectors was linked to the availability of host and breeding substrates13,29. For boophilic species, body volatiles (CO2 as the main kairomone) in combination with their size and color were reported to be important cues for most biting insects30. Fly collections were greatly influenced by sampling gear and their efficiency was enhanced using odorants (CO2) as well as short chain aromatic compounds like acetone and Octenol31.
| Fig. 6(a-d): | (a) Number of tabanids, (b) Muscidae, (c) Simulium/Culicoides and (d) Culicids caught from the screened and non-screened sites |
T- : Unscreened site, T+: Screened site |
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In the case of Nzi and Biconical traps used in this study, their blue-black color cue attracted biting dipterans32. Apart from host and trap properties that influenced fly collections by live bait, trap design was another important element21. These properties also apply to targets (screens) used in insect vector control13. The overall Zerofly® screen model reduction rate was 73.70% and was close to the 100% glossiness reduction obtained already12, 85-100% and 96% using screens33,34. The present observation on screen efficacy was superior to the 36.38% glossines reduction rate reported by Abdoulmoumini et al.13 Deltamethrin impregnated curtains have helped in the protection of humans in Cuba from bites of culicids35. Deltamethrin impregnated nets were used to suppress the population of zoophilic and anthropophilic insect vectors36-39. Based on the reduction rate of individual screens, it was noticed that the IIS had a slightly higher overall percentage reduction than MIS. The probable reason for efficiency discrepancies between the two screens could be related to their size because the IIS was longer and wider as compared to the MIS. It was reported that blue-black fabrics of targets for stable flies showed that size and shape did not influence their efficiency32. Therefore, size of the screen model was not a concrete argument, but it might be due to the long lasting property of the IIS that maintained its integrity throughout the survey as compared to the MIS as well as the blue color intensity discrepancies of the two screen models (IIS was made of phthalogen blue with back portion while the MIS was made of deep blue-black color)10.
However, it was interesting to know that there was no statistical significant difference in the reduction rates of the two screen models. Different fly-species responded differently to the knock down effect of the screen models. The IIS model effectively suppressed individuals of most fly-groups except some few species like S. n. bilineatus, S. omega, S. inornatus and S. damnosum, but these individuals were rather suppressed by the MIS model. The difference in the two trap model reduction rates with regards to individual species mightbe due to the slight differences in the blue portions of the two screen models10-21. The blue color of the IIS model was phthalogen blue and that of the MIS model was deep blue, so these slight differences led to the attractive and knock down discrepancies in the individual species by the two models. It therefore revealed that S. n. bilineatus, S. omega, S. inornatus and S. damnosium were more attracted to dark blue of the MISmodel rather than the light blue of the IIS model. This wasalready noticed and reported that color variations of modifiedbox traps influenced the trapability of insects particularly tabanids40.
Considering the test-control trial for the functionality of screen models, it was noticed that the screened site recorded scanty insect catches for most species as compared to their non-screened counterpart with a statistically significant difference. This observation was similar to that made in Tanzania where ZeroFly® screened herds showed a significant percentage reduction rate in the population of biting flies than in the unscreened herds12.
It should be noted that the ZeroFly® Nzi traps could also play the role of screens, based on their size and their long lasting insecticide impregnated nature. It should also be notedthat the NMA was the site with the highest catches andthe presence of just a ZeroFly® Nzi trap was not enough to maintain low numbers in the site as compared to the GTB which was close to the DFG cattle corral and gallery forest which were highly infested (no vector control) sites and the joint effort of ZeroFly® Nzi and screen models were equally enough to clear the site and maintain low numbers. This indicated that in an insect-vector hyper-infested area, high density of traps and screens are needed to maintain low numbers of the target population10-13.
CONCLUSION
Insect-vectors of medical and veterinary importance wereidentified. The presence of ZeroFly® screen models and ZeroFly® traps led to the suppression of the insect-vector population in the study area. The ZeroFly® IIS reduction rate was higher thanthe MIS counterpart. Because of cost effectiveness, it will be economical to use the MIS that had similar results like theIIS(which was expensive but efficient) and was cheap (blue-black clothing was available in the market) as well as easily reproducible.
SIGNIFICANCE STATEMENT
The study focused on determining the relative efficacy oftwo deltamethrin incorporated ZeroFly® screen models notably the Manually Impregnated Screen (MIS) and Industrially Impregnated Screens (IIS) in the control of hematophagous dipterous insects in the hyper-infested rangeland of Ngaoundere. This is to propose to breeders, a very cheap and efficient approach for vector population suppression. There was no statistically significant difference inthe population reduction rate of insects by the two screen-types. Therefore, the MIS which was cheap compared to the IIS could be proposed to breeders and vector control authorities in Ngaoundere.
ACKNOWLEDGMENT
Authors are grateful to the MSEG for providing insecticides and traps. We also thank the herdsmen for their assistance throughout the study.