Density and Structure ofSaissetia oleae(Hemiptera: Coccidae) Populations on Citrus and Olives: Relative Importance of the Two Annual Generations

Abstract

Saissetia oleae (Olivier) (Hemiptera: Coccidae) populations were studied and compared in citrus (Citrus spp.) and olive (Olea europaea L.) groves to determine the number of generations, crawler emergence periods and changes in population density during the year. Ten citrus and four olive groves were sampled regularly between March 2003 and December 2005 in eastern Spain, covering an area of 10,000 km2. Each sample consisted of 16 branches and 64 leaves. Saissetia oleae populations presented a similar trend in both crops during the three years of study. Populations peaked in July, when crawlers emerged after the egg-laying period, and decreased during several months due to mortality of first instars in summer. A second crawler emergence period, with lower numbers and more variability from year to year, occurred between October and March. Populations did not increase during this period, probably because most eggs and crawlers perished during the winter and also because females that gave rise to this fall-winter generation were half as big and fecund as spring females. No differences were found between the size of mature females that had developed on citrus and on olives during the spring. Considering this population pattern, the best seasonal period to apply pesticides to control S. oleae would be at the end of July, when populations are synchronous, all crawlers have already emerged, and first instars predominate.

Population Dynamics of Saissetia oleae (Olivier) (Hemiptera: Coccidae) on Olives

“…This relation was also observed by Pereira [10] in olive groves and Tena [1] in olive and citrus groves. The volume of the female represents its potential fecundity more accurately than the number of eggs found in a particular moment as discussed by Tena [1].…”

“…Our observations are not similar to those of other western Mediterranean authors, most of Saissetia oleae populations exhibited considerable abundance fluctuations during the year. Population density decreased for several months, especially during the summer, because of high mortality of first-instar scales, Tena [1].…”

“…In Spain, Tena [1], demonstrates that low temperatures synchronized the developmental stages present, and consequently, populations were strongly synchronous after the winter.…”

“…Black scale is known by its high reproductive capacity, the number of eggs laid by the scale range from a few hundreds to 4000 as discussed elsewhere [5] [6]. After hatching, the crawlers move out of the egg chamber beneath the mother's body and they wander over the host plant searching for a suitable place to settle, Tena [1]. In Mediterranean countries, this species may have one generation per year, one and a partial second generation, or two complete generations, depending on crop species, nutrition of the tree, agricultural practices, possibly different strains of S. oleae, and most importantly, climate as discussed elsewhere [6] [7].…”

General Biology and Current Management Approaches of Soft Scale Pests (Hemiptera: Coccidae)

“…(partial 2nd generation) Eastern Spain Citrus, olive ( Bibolini 1958 , Argyriou 1963 , Peleg 1965 , Nuzzaci 1969b , De Freitas 1972 ) June to July (for 1 generation) Eastern Spain Citrus, olive ( Briales and Campos 1986 , Noguera et al. 2003 , Tena et al. 2007 ) Mar.…”