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Infected fruits are usually easy to distinguish from uninfested ones by the hardened, amber-coloured secretion often sculptured with two small angled tails at one end, which remains attached to the site of oviposition (Wadhi, 1964; Ridgway, 1989; Smith, 1996; Peng and Christian, 2004, 2007). Especially, when S. mangiferae populations are high, brown marks at the oviposition sites on mature fruits are very obvious (Smith, 1996; Peng and Christian, 2007). Maheswari and Purushotham (1999) described a simple method of diagnosing the incidence of S. mangiferae on mango based on the appearance of reddish-brown spots and water-soaked areas in the pulp of immature fruit. In rare instances where larvae feed and pupate within the pulp, or when they emerge from the seeds and tunnel up through the pulp, fruits are seriously damaged (Balock and Kozuma, 1964; Follett and Gabbard, 2000).
In South Africa, Kok (1979) showed that after harvest of late-maturing varieties, adults tended to leave the seed and tunnel through the fruit, leaving a scar on the outside which served as a site for secondary fungal infection; this renders the fruit unfit for human consumption. Internally infected fruit rots from the outer surface of the stone. The stones also show holes and the cotyledons turn black and become a rotten mass. Seeds fail to germinate if the embryo is damaged and the reserve of food in the cotyledons is greatly reduced.
The fruit, seeds and also plants of mangoes represent a phytosanitary risk and such material from countries where the pest occurs may be prohibited by mango-growing countries. Mango plants for planting (including seeds) may be imported if they derive from an area where the pest does not occur and the place of production has been found free from infestation by inspection during the previous growing season.
Imported mangoes from countries where S. mangiferae occurs can be subjected to a quarantine treatment. Irradiation is the most effective method of killing or sterilizing weevils within fruit (Follett, 2001). An irradiation dose of 300 Gy is approved for control of mango seed weevil in mangoes exported from Hawaii to the continental USA (US Federal Register, 2002). In South Africa, irradiation of ripe, marketable fruit protected it from damage and prevented adult emergence (Kok, 1979). Hot and cold treatment of fruit has also been tried but gave unreliable results and proved phytotoxic (Balock and Kozuma, 1964; Seo et al., 1970; Shukla and Tandon, 1985).
In Australia, S. mangiferae control is of utmost importance because adult oviposition activities can downgrade the fruit, resulting in reduction in growers’ profit (Smith, 1996; Peng and Christian, 2007). In South Africa, S. mangiferae has to be controlled in orchards where fruit is grown for export market (Villiers, 1987; Joubert, 1997). Also, Follett (2002) and Abraham Verghese et al. (2005) showed the importance of controlling S. mangiferae because seed weevil infestation can increase fruit drop during the early fruit developmental stage. In other mango-growing regions, there is little incentive for growers to attempt control because the eating qualities of the fruit are usually unaffected.
Cultural control and sanitary measures
Good orchard sanitation is an effective way to reduce adult populations, and this involves the destruction of all the fallen fruit, stones and fruits with seed weevil damage during and immediately after mango harvest (Wheatley, 1960; Kok, 1979; Villiers, 1987; Peng and Christian, 2004).
In nursery beds, more seeds than are required for the projected number of seedlings can be planted to allow for a lower percentage of germination. Alternatively, the seed may be shelled and only sound kernels planted (O'Connor, 1969).
The ant Oecophylla smaragdina is an effective biocontrol agent of S. mangiferae adults (Peng and Christian, 2004, 2007). A method of using Oecophylla ants together with orchard sanitation has been developed for controlling S. mangiferae, and is promoted by the Horticulture Division of Northern Territory Government, Australia (Peng and Christian, 2005).
Host plant resistance
In India, ten cultivars (out of 92 studied) were found to be free from S. mangiferae infestation, and these cultivars are Sindhu, Bombay Green, Firangi Ludua, Pulihora, Jahangir, Sabja, Salgadino, Hatizool, Dodamio and Fazri (Godse and Bhole, 2003). Larval penetration of the seed of the variety Itamaraca is reported to be impossible (Balock and Kozuma, 1964).
Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources: