SUMMARYA working hypothesis that a latent factor is involved in mealybug wilt was adopted.The toxic effects of mealybug feeding, apart from mealybug wilt, were demonstrated by the use of mealybugs from host plants not susceptible to wilt and by previously unfed colonies of mealybugs.These toxic effects, interpreted as inducing conditions of stress, were expressed in growth depression, accentuation of normal color characteristics, and premature fruiting.Virgin colony feeding can increase the susceptibility of pineapple plants to wilt and can also induce wilt if the test plants are positive sources.There is sometimes a considerable lag in time between the insect's feeding and the expression of symptoms of the resulting toxicity.Two examples are recorded of symptoms of genetic weakness being forced into expression by virgin colony feeding or by mealybugs from sisal or grasses.The wilt‐inducing secretion is believed to be the result of a synthesis by the mealybug, the effectiveness of the mealybugs being governed by the physiological activity of the leaves on which they feed and the number of mealybugs involved.The capacity to induce wilt is lost if an intermediate feeding as a negative source plant is interposed between the positive source feeding and feeding on the test plant. This is interpreted as an exhaustion process.The existence of a latent factor has been demonstrated by establishment of positive source value in the absence of wilting. The influence of virgin colony feeding, after inoculation feeding but not before, is clearly shown.The mature green distal leaf tissue is not receptive to the latent factor although the mealybug can synthesize the wilt secretion on such tissue. There is evidence that Phenacoccus solani (Ferris) can, in some circumstances, transmit the latent factor although it has not thus far induced wilt.The hypothesis that the insect's secretions activate the latent factor is rejected; instead, the insect's normal secretions as typified by those from the previously unfed insects, increase the concentration and/or distribution of the latent factor in the plant. The insect's secretion causing wilt is believed to be synthesized by the mealybug when it feeds on a plant which has been modified as a nutrional substratum for the mealybug by the presence of the latent factor.Since the latent factor is transmissible and retained in a vegetatively reproduced plant it is presumed to be a latent virus. Its retention at demonstrable levels is aided by the feeding of fairly large mealybug colonies. The rarity of such colonies in commercial fields accounts therefore for the relative rarity of positive source plants and the almost complete absence of mealybug wilt.
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Jan 1, 1991
Diane E Ullman 
Open Access