Incidence, size and structure of grapevine infesting groups of Kalotermes flavicollis (Isoptera: Kalotermitidae) in Sherry vineyards (Spain)

Grapevine trunks in Sherry vineyards (Andalusia, SW Spain), yielding important registered designation of origin wines, are seriously affected by the drywood termite Kalotermesflavicollis. In order to analyze the patterns and extent of occurrence of the infesting groups, a 16-month-long investigation was performed, during which termites collected from each colonized grapevine trunk were recognized and counted according to the developmental stage or caste and the variation of caste proportions according to group size and season of occurrence was investigated. Results showed that different grapevine trunks exhibited different degrees of infestation, ranging from minuscule (0-50 individuals) to very large (more than 1000). Evaluating the composition and the occurrence of the colonizing groups, it was possible to determine that: a) minuscule groups, composed especially by eggs, reproductives, younger developmental stages and no alate adults, were probably 1-3 year old incipient colonies and occupied 12.6% of the infested grapevines; b) all groups with more than 50 individuals exhibited higher percentages of nymphal stages and, during fall, a considerable fraction (from 1/12 to 1/3) of the population was represented by alates, suggesting that they were mature colonies at different degrees of development. The greater part (64.2%) of infested vines were attacked by small-medium size colonies with a few hundred termites (51-700) and about 8% alates. Groups with the highest potential of infestation such as large colonies (up to 1000 units and 20% alates) and very large ones (1000-1692 individuals and 34% alates) were found respectively in 14.7% and 8.4% of termite colonized grapevines. The importance of these findings for the management of Sherry vineyards is discussed.