Effects of Cassava Pubescence on the Behaviour, Post-Embryonic Development and Reproduction of the Cassava Mealybug, Phenacoccus manihoti Matile-Ferrero (Homoptera: Pseudococcidae)

Abstract

Role of trichome density in cassava resistance to mealybug, Phenacoccus manihoti Matile-Ferrero was evaluated on the apex, the first expanded leaf and the stem in pubescent and glabrous cassava varieties. Pubescence significantly retarded the rate of settling and establishment of P. manihoti. The weight of the developing larvae was also affected becoming more pronounced at the pre-ovipositing adult stage. However, the relationship between pubescence and P. manihoti weight was not significant. Moreover, the significant differences in weight at the preovipositing adult stage was not reflected in the corresponding fecundity on the glabrous and pubescent varieties. Pubescence accounted for only 18% of the differences in observed fecundity. There was also no significant difference in the development period of the mealybug on glabrous and pubescent varieties. Pubescence appeared to be a mechanical irritant only.

Résumé

Deux types de varietes de manioc, glabre et pubescente, ont ete soumis a l’etude due comportement, du developpement post-embryonnaire et de reproduction de la cochenille farineuse du manioc, Phenacoccus manihoti Matile-Ferrero, dans les conditions de serre, aux temperature et humidite relative moyennes de 30.2° C et 72.4% respectivement.

L’infestation de varietes pubescentes etait forterment retardee jusqu’a affecter le poids vif des larves de deuxieme et troisieme stades; l’effet etait plus prononcee sur le stade de preoviposition. Aucune observation similaire, tributaire a la pubescence, n’etait faite au sujet de la fecondite de l’insecte sur les plantes soit hirsutes ou glabres; 18% de differences observees sur la fecondite decoulaient de la pubescence. Aucune difference significative n’etait observee dans la duree de developpement de cochenilles sur les deux types de varietes de manioc. Dans les conditions experimentales presentes, la pilosite, chez le manioc semble exercer un role irritant sur la cochenille farineuse.