San Jose scale - Reproduction

San Jose scale has both male and female adults and relies strictly on sexual reproduction. The sex ratio is about 1:1, although delayed mating can result in a higher proportion of male offspring. The female produces a sex pheromone which attracts the winged males for mating. Pheromone release is timed during the day when males are active. Males fly for up to a few days after emergence and may locate females after flight or by walking over the bark of the host tree. The identified pheromone components of San Jose scale are:
(Z)-3,7-dimethyl-2,7-octadien-1-yl propanoate (48%), 7-methyl-3-methylene-7-octen-1-yl propanoate (47%), and (E)-3,7-dimethyl-2,7-octadien-1-yl propanoate (5%).
Various mixtures of these chemicals have been used as bait in pheromone traps for monitoring the flight of San Jose scale males. Male (and female) San Jose scale are able to mate almost immediately after emergence and multiple mating may occur. In mating the female scale insect lifts her scale covering slightly to exsert a structure called the pygidium which contains the pheromone glands. There have been a number of attempts to improve scale control by timing sprays for this event and the presence of the males, whose mobility increases the chances of contact with insecticides. Females cease or reduce pheromone release after insemination.

Female San Jose scale insects give birth to live crawlers (viviparous), by-passing the egg laying stage which occurs in some related species such as oystershell scale, Quadraspidiotus ostreaeformis. Females have a period of about 30 days after reaching adult before they begin to produce crawlers, but this continues for 40-60 days and results in large numbers of offspring (see fecundity). This very high rate of reproduction, combined with multiple generations per year, enables populations of San Jose scale to build rapidly and cause severe damage to apple trees, including death of limbs and even entire young trees.