Varietal influence of orange trees on armoured scale insect fecundity (Hemiptera: Diaspididae)

Abstract

We studied the influence of two orange tree varieties on the fecundity of two hemipteran diaspidid scale insect species: Cornuaspis beckii (Newman) and Parlatoria pergandii Comstock. Samples of females were taken at 7 – 40 day intervals from two orange orchards [Citrus sinensis (L.) Osbeck], one of the Navel Lane Late cultivar and the other of the Valencia Late cultivar. Different categories for the egg stage were considered: preoviposited, oviposited and hatched eggs. Average fecundity in C. beckii was significantly higher than that of P. pergandii. Significant differences between the two orange varieties were evident for some egg categories, with a higher fecundity in Navel Lane Late than in Valencia Late. The temporal pattern of fecundity in relation to accumulated temperature was studied by two methods: (i) comparing the parameter r of a logistic function that related egg-days to accumulated degree-days, and (ii) comparing the parameters b and c of a sinusoidal function that relates the variation egg-days/degree-days to accumulated degree-days. The comparison of such parameters (indicators of changes in the temporal patterns of fecundity) did not show significant differences between orange varieties. Our results suggest that some type of physiological difference between Navel Lane Late and Valencia varieties could be responsible for the differential fecundity of diaspines. Nevertheless, currently we cannot recommend changes in the management of diaspine in citrus orchards.