Ants and mealybugs

Mealybug wilt of pineapple, with its leaf-tip dieback and plant yellowing and reddening, is a symptom associated with the feeding of mealybugs (Plate 26). The actual cause has not been conclusively demonstrated, but one or two closteroviruses have been implicated (Sether and Hu, 1999). Mealybug wilt is a universal problem; the only exception may be in parts of Thailand, where wilt does not occur even though mealybugs are present. Mealybug wilt is clearly one of the most destructive diseases of pineapple plants, and field controls must be initiated during the fallow period and continued to harvest. High mealybug populations are required to cause wilt. Ants are necessary for populations of mealybugs to develop and reproduce in pineapple fields, where mealybug

Fig. 9.16. Pineapple root system showing soil sticking to reniform nematode egg masses (arrow) and the lack of secondary roots.

parasitoids and predators are present. At least three species of ants are associated with mealybugs in Hawaii: the big-headed ant, the Argentine ant and the fire ant (Rohrbach and Schmitt, 1994). Two other species - the long-legged crazy ant, Anoplolepis longipes (Jardon), and the white-footed ant, Technomyrmex albipes (Fr. Smith) - are clearly associated with mealybugs in pineapple fields and, although not demonstrated to be associated with wilt, may have a role because they clearly tend mealybugs (G. Taniguchi, personal communication). The ant association with mealybugs involves protection from predation and parasitism, removal of excess honeydew, which increases mealybug mortality and movement of the mealybugs into new areas. Preventing the establishment of new ant colonies in new plantings is critical to preventing mealybug wilt (Rohrbach and Schmitt, 1994).

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