Assessing Effectiveness of Climate Smart Activities: A Study from Rural Areas, Nepal-Juniper Publishers

Journal of Agriculture Research- Juniper Publishers


Abstract

The White mango scale (WMS) distribution, population dynamics and severity status was conducted in southwestern part of Ethiopia. Purposive sampling was used to select districts growing mangos. The existence of the WMS was confirmed by visual assessment in the field and using a stereo microscope in the laboratory. The population dynamics of the WMS was studied in two locations in west Welega zone (Didesa Valley and Uke farms) and one location in west shoa zone (Bako tibe district). Leaf samples were collected from the four cardinal directions of the mid canopy of five tagged trees every month for 12 consecutive months. The number of eggs, crawlers, male’s colonies and females were recorded using stereo microscope. High to very-high infestations were recorded in all the surveyed areas while exceptionally low populations were observed in some districts of Jimma, Kafa and Ilu-Abba bora and west Welega. Population dynamics of WMS reach the maximum peak in April in Didesa and Green focus sites while at Bako site the population reached its climax in May. The correlation study showed that the populations of the WMS are except maximum temperature positively correlated with weather factors. During study we recorded more WMS population density in south and west directions. Therefore, management interventions should be planned accordingly to coincide with the peak population periods and distribution directionality. This study has indicated that the WMS problem is serious in southwestern Ethiopia..
Keywords: White mango scale; Distribution; Severity status; Population dynamics
Abbreviations: WMS: White Mango Scale; Spp: Species; CV: Coefficient of Variation; LSD: Least Significance Difference; EIAR: Ethiopian Institute of Agricultural Research; SNNP: Sothern Nations Nationalities and Peoples; APPRC: Ambo Plant Protection Research Center


Introduction

The white mango scale (WMS) (Aulacaspis tubercularis) originated in Asia and was later distributed all over the world, is currently constraining the cultivation of mangos worldwide. CABI distribution map of pests show that A. tubercularis occurs in several countries of West Africa and several Sub-Saharan African countries [1]. In Ethiopia, the WMS was first reported in east Welega zone of the Oromia region in August, 2010 at a private farm (Green Focus Ethiopia Ltd). The pest can attack crops such as citrus, papaya, avocado, ginger, cinnamon, and pumpkin [2].
The study of the distribution and severity status of the WMS in east and west Welega zones and confirmed that maximum air distance covered by the WMS was 67km to the west (Gimbi district- Jogir kebele), on the way from Nekemte to Asossa, and 58km to the east (Gobu Sayo district-Sombo Kejo kebele), on the way from Nekemte it make reference from the WMS insect original infestation place at Guto Gida district (Loko Adiministrative kebele) [3]. There are no other recent studies on the distribution and severity status of the WMS in the south western part of Ethiopia. Knowledge of pest fluctuations in their ecology is very important along with weather factors that influence their population. However, there is no detail data concerning white mango scale population dynamics in Ethiopia. Therefore, these studies aimed at determining the distribution, severity status and the population dynamics of the WMS in south western Ethiopia.


Materials and Methods

Study area

Surveys were undertaken in south -western parts of Ethiopia during the 2016/2017 cropping season to study the distribution and severity status of the WMS (Aulacaspis tubercularis). The survey covered four major mango producing regions, viz: Sothern Nations, Nationalities, and Peoples (SNNP), Oromia, Gambella and Benshul-Gumuz. This survey was carried out in ten (10) Zones, 43 districts and 97 sites. The survey started from east Welega zone, Guto-Gida district where the WMS was first reported in Ethiopia. Purposive sampling was used to select sampling sites depending on availability of mango farms/trees along road side at 5 to 10km intervals and leaf samples were collected. From each sampling site 5 mango plants were randomly selected, and sixteen leaves were collected from the mid canopy of the trees from four cardinal directions (North, South, West and East). In the case of the population dynamics studies, studies were carried out in western Oromia; east Welega (Didesa valley and Uke farm (Currently, Raj Agro-industry) and west Shoa (Bako-Tibe). Five mango trees similar in size and age were selected and marked at each site for this study. Samples were collected monthly during the period from October 2017 to September 2018. From each tree 20 leaves were collected from cardinal directions (North, South east and West) of the tree (four leaves per direction). Geographic data (Longitude, Latitude and Altitude) of each sampling site were recorded using a GPS. Weather factors such as maximum, minimum and mean of both temperature and relative humidity


Results and Discussion

Distribution and severity status

The present survey revealed that there were irregular patterns of white mango scale distribution and severity in south western party of Ethiopia. The pest was observed causing various degrees of severity in all surveyed areas (Table 1&2). Except some district of Jimma, Ilu-abba bora and west Welega, high to very high infestations were recorded in all surveyed areas with high numbers of white mango scale life stages (Table 1&2). During the survey WMS free mangos were recorded at Jimma zone (Sokoru,Saka, Shabe, Gumma, districts), Ilu-abba bora zone (Halu district) and west wellega (Mandi and Najo districts) (Table 3). There was significant difference in WMS life stages population densities recorded among the different districts. Population density of WMS life stages recorded at East Welega: High population density of White mango scale in these Zones resulted in high to very high severity status on mango trees in these particular zones (Table 3). Researchers reported that the white mango scale has the potential to devastate mango trees in Ethiopia [3,6].
Severely infested mango trees were observed with dry leaves and small sized fruits mostly infested by female white scales which usually drop early. Currently it has been reported that under heavy infestation premature fruit drop and smaller size is common [7]. The variations in population density recorded in the various administrative zones is probably caused by varietal difference, ecological variation, cultural practices of the individual farmers, elevation of the area, mango tree population scattered over surveyed areas and time of arrival of white mango scale to the area. According to Sunji (Personal communication) severity of white mango scale at Green focus (Raji agro-industry) varied across the different mango varieties in the farm. According to Sunji, the varieties Alphanso, Kent, Tommy Atkins and Dodo are susceptible to white mango scale. In contrast the varieties Apple and Keit are more tolerant to this pest.
This survey result indicates that spread of this insect is expanding to all western part of the country. The distribution of white mango scale probably facilitated by wind which may transports nymphal (crawlers) stage to neighboring plants. The report showed that white mango scale can move with the help of external forces like wind, birds and insect pests [8]. The WMS female is flightless insect but is mobile only at nymphal (crawler) stage. In addition to this long-distance dispersal of white mango scale life stages is also possible if infested planting materials (Leaves, twigs, fruits) and contaminated containers are transported within or outside infested areas (Figure 1).

Population dynamics

The WMS population data from October 2016 to September, 2017 indicates that, in all the three surveyed area, the population dynamics follow almost the same pattern. The number of WMS recorded was exponentially increased from October to March and reach the maximum peak in April in Didesa and Green focus sites (Figure 2A, 2B & 2C). After the month of April, the population dramatically declined through May and June, and then slightly increased in July. In case of Bako site, the population of WMS increased from October to April and reached the climax in May and declined through June to September. Similar report with this finding, three peaks per year in Egypt was recorded [9]. Similarly, the groups stated that the population peaks of the pest occurred during different periods of the year [10]. At Didesa valley the correlation analysis revealed that WMS life stage population showed that a very weak positive correlation with mean temperature (r=0.059), weak negative correlation with maximum temperature and weak positive correlation with relative humidity respectively recorded. At Green focus very weak positive correlation with mean temperature and moderate correlation with Maximum temperature and strong positive correlation with maximum relative humidity were recorded. In case of Bako site very weak positive correlation with mean relative humidity and moderate negative maximum temperature were recorded (Table 3). Data in table showed that in all sites Maximum temperature recorded with negative correlation with white mango scale population. WMS population peaks mainly depend on temperature and relative humidity of that locality [10]. Whether factors particularly the effect of temperature on insect biological behavior such as distribution and reproduction of insects, population size and sex ratio [11].
*Correlation is significant at the 0.05 level, **Correlation is significant at the 0.01 level
Note: Absolute value of r: .00-.19 “very weak”, 0.20-.39 “weak”, 0 .40-.59 “moderate”, 0 .60-.79 “strong” and 0 .80-1.0 “very strong” (Evans (1996).

Distribution within a tree

Didesa valley site: The distribution of the WMS significantly differences among the different cardinal directions. High numbers of WMS individuals per leaf were recorded in the South direction while lowest population was recorded in East direction and North direction. At Green focus except female all show significant difference among all direction. At this site we recorded high populations of individual per leaf in south and west direction (Table 2). At Bako site crawlers and females show significant difference in all direction. In current study we recorded high individuals per leaf in south and west direction respectively. The WMS life stage variation observed in present study probably caused by directional variation in weather factors such as wind force that may directly resist crawler establishment and indirectly increases evaporation that reduce moisture level, temperature difference, light intensity that may cause mortality during dry seasons. Labuschagne and his colleague’s demonstration showed that south face is more prone than other face due weather factors differences (Table 4) [10].


Conclusion

The current survey showed that WMS distribution is expanding to all southwestern part of Ethiopia and considerably threatening mongo tree production and productivity. We observed very low population density (severity status) and white WMS free mango at Jimma zone (Sokoru, Saka, Shabe, Gumma, Gumayit district), Iluabba bora Zone (Halu district) and West welega (Mandi and Najo district). Population dynamics of WMS increased from October to March and reach the maximum peak in April in Didesa and Green focus sites. In case of Bako site, the population of WMS increased from October to April and reached the climax in May. In current study we recommend that during chemical spray emphasis need to be taken in south and west directions. From current study we recommend that regulatory measures, information dissemination need to be regularly updated though surveillance and monitoring activity to keep the population below economic threshold level particularly where infestation is low.
Coordination system among farmers, plant extension groups, healthy clinic, and professional expert should be facilitated and strengthen to minimize the risk. Movement of infested plants and plant products (fruit) from infested districts need to be prohibited through regular inspection. Management options such as conservation, unproductive large mango trees (source of inoculation) replacement, enhancing tolerant and manageable size mango variety, clustering mango potential zones, developing mango production package should be initiated by governmental intervention. IPM such as pruning, burn heavily infested branches, systemic insecticide, improving chemical application methods (soil drench, tree injection, modifying spraying mechanism for larger canopy of mango tree), enhancing native natural enemies population build up through rearing and re-inoculation, introduction of exotic natural enemies such as parasitoid need to be design as soon as possible for highly infested area such as Bench-Maji, East Wellega, West shoa zone and Assosa region to minimize the population size of white mango scale.


Acknowledgement

The author expresses sincere thanks to Green Focus private farm for their permission during insect record. We acknowledge Ato Dejene Hordefa (technical assistant) for his support during data collection. The study was financially supported by the Ethiopian Institute of Agricultural Research (EIAR).

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