Temporal distribution of San Jose scale Diaspidiotus perniciosus (Hemiptera: Diaspididae) on an apple tree

San José scale (Diaspidiotus perniciosus) on a 'Red Delicious' apple tree (Malus x domestica) was sampled fortnightly from September 1969 to September 1970 at Nelson, New Zealand. With the exception of crawlers, all live and dead stages of San José scale were counted on bark samples of known surface area from the trunk, leaders, main branches, twigs, fruit spurs and new shoots. Random samples were taken from strata below, within and above five infestations on the trunk and main leaders. Similarly, scale insect stages on leaves and fruit of the sampled twigs, fruit spurs and shoots were counted. At harvest, the total numbers of scale insects on each fruit remaining in each stratum were recorded. Although all stages were present in winter, overwintering was achieved primarily by the settled 1st instar (May, June) and then by the 2nd instar (July, August). Moulting by these 2nd instars in August/September resulted in a clearly defined first generation of adults and their progeny. The short life of the males enabled identification of at least two further generations of males in January and March to May, which possibly included a partial fourth generation. Overlapping of generations of longer-lived adult females and immatures prevented clear identification of their generations after crawler production (second generation) in February. Few first generation crawlers infested the fruit (<7% of the total at harvest). Monitoring of dead 1st instars indicated that they had died largely within the current generation, but some dead 2nd instars and adults arose from preceding generations. Nevertheless, the only evidence of carry-over of dead insects from season to season was briefly in spring for the overwintered 2nd instars. Where spraying against San José scale is necessary in summer, this must be no later than February, to protect fruit from dispersing crawlers of the second generation. Alternatively, spraying in November/December against first generation crawlers could complement winter treatment with oil in keeping San José scale below economic thresholds. © 2013 The Entomological Society of New Zealand.