Abstract:
The mutual association between honeydew foraging ants and vine mealybugs in
vineyards is detrimental to the biological control of the vine mealybug Planococcus
ficus (Signoret). This study investigated the relationship between ants, vine mealybugs
and their parasitoids to improve biological control of the vine mealybug. The
investigation was carried out during two consecutive growing seasons (2005-2006 and
2006-2007) in two major wine grape growing areas of the Western Cape Province,
Simondium (two farms) and Breede River Valley (one farm). A presence – absence
cluster sampling system was used on a biweekly basis throughout both growing seasons
from October to February on each of the farms. Additionally, yellow delta traps with
vine mealybug pheromone, were used to catch parasitoids in vineyards. Prior to harvest,
economic damage to grape bunches was assessed using a 0-3 damage rating index.
Three ant species, Anoplolepis steingroeveri (Forel), Crematogaster peringueyi Emery
and Linepithema humile (Mayr) foraged mainly on vine stems during both seasons,
relative to other plant parts. Vine mealybugs of all stages were found on all sampling
dates. Three species of primary parasitoids attacked the vine mealybug, including
Anagyrus sp. near pseudococci (Girault), Coccidoxenoides perminutus (Timberlake)
and Leptomastix dactylopii Howard. Bunch damage was significantly different between
seasons in the Breede River Valley but not in Simondium. There was a negative linear
relationship between ants and parasitoid activity in all vineyards. Spatial Analysis by
Distance IndicEs (SADIE) was used to analyse spatial distribution of ants and
parasitoids and ArcView, with its extension, Spatial Analyst, were used to map the gap,
patch and local association indices where significant association and disassociation
occurred. A significant association was found between C. peringueyi and parasitoids
and L. humile and parasitoids. There was a significant disassociation between L. humile
and C. peringueyi and between A. steingroeveri and C. peringueyi indicating
interspecific hostility.
