The cassava mealybug Phenacoccus herreni Cox Williams (Sternorrhyncha: Pseudococcidae) is an important pest of cassava, Manihot esculenta Crantz (Euphorbiaceae), especially during drought, when insect population's increase. This phenomenon might be a response to biochemical changes in cassava leaves induced by water deficiency, which enhances insect development. In order to verify this phenomenon it was first necessary to study its feeding behavior. Observation of the mouthpart by scanning electron microscopy and fase contrast microscopy were carried out and the feeding activity was studied by electropenetrography (EPG). Insect biological development and reproductive rate, and also infested leaf aminoacid composition from cassava plants grown with differential irrigation levels (well watered and deficiently watered) were evaluated. The influence on P. herreni development of the aminoacids that increased their proportion in water stressed plants was evaluated using an artificial diet. The results showed that P. herreni is mainly a phloemophagous insect with piercing-sucking mouthpart that is present in females throughout their life cycle. Male insects showed the same mouthpart only till the second ínstar. The fact that the females maintain their piercing-sucking mouthpart and they feed on phloem sap throughout their life cycle, we suggest that the females are more responsible for cassava damage and therefore subsequent studies were done on females. Water stress in plants induced a reduction in the duration on female development and an increase in fecundity, intrinsic natural growth rate (rm) and in weight. Leaf aminoacid composition showed a more important increase in the proportion of free asparagine. Using an artificial diet it was shown that this aminoacid may play an important role during the development of P. herreni. In fact, its absence in the diet induced an insect development delay.

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Feeding behavior of the mealybug Phenacoccus herreni (Sternorrhyncha: Pseudococcidae) and influence of water deficiency in cassava plants on its development