Encyclopedia
Please note this is a comparison between Version 1 by Asifa Hameed and Version 2 by Rita Xu.
The white mango scale (WMS) insect,
Aulacaspis tubercularis
(Hemiptera: Diaspididae), is a polyphagous, multivoltine pest which is a serious threat to qualitative mango production and export. The WMS insect sucks sap from leaves, branches and fruits. The heavy infestation of this pest may cause the falling of young leaves, drying up of twigs, poor flowering, and, finally, reduce the quality of fruits by producing pink spots on fruits’ surface.
- Aulacaspis tubercularis
- environmental variables
- damage
- cultural control
1. Introduction
Mango (Mangifera indica Linn. Family: Anacardiace), the so-called “King of fruits”, is an important fruit crop throughout the world, including Pakistan. Mango fruits are popular because they are delicious and rich in vitamins A and C. Good flavor and taste add further value to this fruit. In recent years, mango production has been decreased by multiple factors, viz., nutrients deficiency, flood, drought, thermal regimes, improper management practices (ploughing and intercropping) [1][2][1,2], and biotic factors (insect pests and diseases) [3][4][3,4]. The most prevalent insect pests in Pakistan are scales (Aulacaspis tubercularis (Newstead)), mango hopper (Idioscopus clypealis (Lethierry)), midges (Dasineura amaramanjarae (Grover)), mealybug (Droschia mangiferae), fruit fly (Bacrtrocera dorsalis (Hendel) and Bactrocera zonata (Saunders)), thrips (Scirtothrips dorsalis (Hood)), and bark beetle (Hypocryphalus mangiferae (Stebbing)) [5][6][5,6].
In recent years, white mango scale (Aulacaspis tubercularis Newstead; Diaspididae; Hemiptera) has increased to the extent that it is now regarded as an important economically destructive and potential export risk in different parts of the world [7][8][7,8] including south-east Asia. This pest was first reported on the island of Formosa on Mangifera indica in 1929, and later on in the Caribbean Islands (2012), India and Brazil (2021) [9]. A. tubercularis originated from Asia [9] and later on it was observed in South Africa [10][11][10,11], Australia, East and West Africa, North and South America and the Caribbean Islands [12]. Now it is found in almost 69 mango-producing countries of the world, and being polyphagous in nature, this pest attacks several crops. The damage of the pest is always variable depending upon the climate and mango variety. This sucking insect pest can be observed on different parts of mango plants, including shoots, twigs, leaves, branches and fruits (Figure 1).
Figure 1. White mango scale insect on leaves and fruit in farmer orchards in Pakistan. (A) WMS population on leaves. (B) WMS population on fruit.
2. Occurrence
WMS (A. tubercularis) had been considered a native to the Asian continent; however, later on, it was distributed in other mango-producing countries through infested plant material [13][14]. WMS infestation has been reported in more than 60 mango-growing countries, including Africa, Asia, Oceania, South and Central America, parts of Europe and the 80 Caribbean islands [14][15].
In Mexico, this pest was first detected in 1999 on 300 acres, and later on, due to extensive damage caused by the pest, it has been regarded as the second most important mango pest after fruit flies (Anastrepha sp.; Diptera: Tephritidae) [15][16]. Morsi et al. [16][17] observed WMS in Minia (Egypt); later on, the pest was observed in all mango-growing areas of Egypt. In Ethiopia, WMS infestation was first reported in 2010 [17][18]. Late on, it became a serious threat to mango productivity in western Ethiopia [18][19][19,20]. In Spain and Andalusia, WMS caused extensive damage to mango production during 2010 (Málaga and Granada provinces) [20][21].
In 1947, WMS was observed in South Africa on a few mango cultivars; later on, the pest was also observed feeding on avocados in South Africa [21][22]. WMS moved from South Asia to Ethiopia through the import of mango seedlings in 2010 [17][18] and further dispersed 100 km west of the original site within a year in the same way [18][19]. Global dispersal of this devastating insect pest was observed through the movement of infested material.
North Atlantic Plant Protection Organization (NAPPO) [22][23] considered this as an important pest and put it on the alert list, but European countries, EPPO, although considering it as an important pest, did not place it on the threat list [20][21]. WMS is considered an important pest in the Mediterranean basin, and strict quarantine measures are implemented to restrict its dispersal.
3. Epidemiological Requirement
Climatic factors, viz., temperature, relative humidity, hurricane, and wind, affect the abundance of WMS [23][41]. The population of WMS, insect physiology and insect behavior were also affected by environmental factors [24][25][42,43], host plants, competitors and natural enemies [26][27][30,44]. Temperature can even affect the male-female ratio. Females were most abundant between 18–22 °C and 73–78% RH while males were abundant at temperatures between 25–28 °C and 66–71% RH [28][45]. At times of peak abundance, 1:20 female to male was observed [28][45].
WMS (A. tubercularis) males cluster in the lower canopy of trees [28][45]. Although females are homogeneously distributed in trees, when the temperature increases, they migrate to lower plant canopy [28][45]. After emergence, males cluster around new virgin females and copulate. Males survive 1–2 days after emergence and do not feed. First, instar nymphs can travel and disperse through winds to the new tree. After reaching there, they establish a colony. However, infested plant material movement from one place to another place for export, movement through birds carrying food in claws, wind and irrigation water can spread the pest in the whole orchard or distant orchards as well.
4. Damage
WMS is a cosmopolitan, highly fecundate and polyphagous pest (feeding on crops belonging to more than 30 different genera and over 18 families [14][29][30][15,46,47]. The pest was abundant on host plants belonging to four families, i.e., Anacardiaceae, Lauraceae, Palmae, and Rutaceae, particularly mangoes and cinnamon [31][32][48,49].
WMS is a serious pest of mangoes [33][50] in Argentina [34][51], Australia [35][52], Brazil [36][53], China [37][54], Colombia [38][55], Ecuador [39][56], Egypt [40][28], Ethiopia [41][57], India [37][54], Kenya [42][58], Mexico [43][59], Pakistan [37][54], South Africa [44][60], Spain [20][21] and many other countries [14][15].
The losses caused by this pest on mangoes varied based on the prevailing climate, variety and pest population. For example, in Kenya, it was not considered an important pest by the mango community as its impact was less serious [42][58], while in other countries such as Ethiopia [19][20], Egypt [45][61] and South Africa [46][62], the pest threatened production.
WMS feeds on plant parts, including fruits, through sucking cell sap. The infestation of WMS results in deformations which ultimately affect plant yield. WMS, during feeding, releases toxic saliva that affects the commercial value of fruits and their export. Greater damage was noticed in late mango cultivars [47][48][29,63] due to the abundance of scales on fruits and quantitative and qualitative damage produced [49][50][64,65].
The less mobile nature of the pest, the presence of chlorotic spots on the leaves and twigs, and less conspicuous blemishes on fruit skin might have been overlooked by farming communities in some countries (for example, in Kenya) [51][52][66,67]. Leaf loss and death of twigs were common in young trees, especially during hot and dry weather [40][28]. Small mango plants in nurseries could die because of heavy infestation of pests at the juvenile stage [51][53][66,68]. Mild infestation of WMS in the nursery may delay mango growth in the nursery, particularly during hot, dry seasons [54][69]. Due to the infestation of WMS, the plant photosynthesis process is affected; hence the leaves change color from green to pale yellow [55][70] (Figure 2).
Figure 2. White mango scale damage on leaves and fruit in farmer orchards in Pakistan. (A) Chlorosis on leaves due to WMS infestation (B) Chlorotic spots on fruits due to WMS infestation in Pakistan.
The conspicuous blemishes on mango fruit skin not only reduce the export of mango fruits but also enhance the economic losses to farmers as well as to exporters [56][71]. The volatiles and odors emitted from ripening fruits might have attracted WMS because the fruits are filled with sugars on which insects feed [57][72]. More than 50% of losses in exports of mango fruits have been recorded due to the presence of chlorotic spots on the epidermis [37][43][46][54,59,62].
When the pest is abundant in mango crops, it is observed on all plant parts, including leaves, twigs, and fruits [58][73]. The odors released by ripening fruits attract the female WMS; hence they are highly abundant on the fruit at the ripening stage [19][58][20,73]. However, less acidic, viscous and sweet ripened mangoes may be more attractive compared to the immature ones due to their biochemical composition [59][60][61][24,74,75].
The management costs and economic losses caused by soft-scale infestations throughout the world have reached greater than one billion US dollars annually [62][76]. In Kenya, farmers spend about 13% of the mango orchard income on the management of WMS [42][58]. In Germany, 97% and 67% of mango fruits were rejected due to scales insect infestation on cultivar Sensation and Fascell, respectively [35][52].
About four–five A. tubercularis per fruit had caused up to 50% loss in commercial orchards in Spain due to the downgrading of mango fruits’ cosmetic value. However, the susceptibility of mango cultivars to WMS infestation varies based on different characteristics. In this regard, a study was conducted in Puerto Rico, where it was concluded that the Haden, Edward and David Haden cultivars were most susceptible to scale insects infestation, while the Irwin and Keitt cultivars were less susceptible and Palmer was the most resistant [63][77]. Mango scale insect infestation in mango orchards of small farmers resulted in less production and reduced quality as well [18][19].
Due to severe infestation of WMS on citrus and fern, chlorotic spots were produced [64][78]. WMS was reported on citrus in Egypt [65][79]. An increase in one WMS per mango leaf decreased fruit yields by up to 4.28 kg per tree per year [54][69].
