Movement of grape mealybug,Pseudococcus maritimus,on and between host plants

The importance of the grape mealybug, Pseudococcus maritimus (Ehrhorn) (Homoptera: Pseudococcidae), as a pest of wine grapes, Vitis vinifera L. (Vitaceae), has increased as a result of recent reports that it is capable of transmitting at least one of the viruses associated with grapevine leafroll disease. However, its natural rate of movement between host plants – and hence its role in the epidemiology of this disease – is poorly understood. In order to better assess the risk of field spread of leafroll disease by this insect, several experiments were conducted to determine the extent to which P. maritimus can move between grape plants, both by walking and by airborne dispersal. In experiments with first instars, both field and shade‐house studies indicated that the mealybugs do not walk far and only very rarely reach adjacent plants by this means. Field trapping experiments showed that grape mealybugs can be dispersed by wind, but that there is a marked decline in numbers with increasing distance from the source plant. The implications of these observations for the field spread and management of grapevine leafroll disease are discussed.