INJURIOUS AND BENEFICIAL INSECTS OP CALIFORNIA. 107 



anthenmm, goldenrod, groundsel tree (Baccharis spp.), ragweed, Rud- 

 beckia spp., rosin weed and thistle (Cirsium). To this list W. M. 

 Davidson also adds the fuller's teasel. 



COCCID^ (Family) 



SCALE INSECTS 



To the California horticulturist, and. especially to the citrus fruit 

 grower, the scale insects are known .to be by far the most destructive, 

 persistent and expensive pests. More money is spent combatting 

 three or four of them than for all other insects combined. To the 

 nurserymen and florists, too, these insects are ever present annoy- 

 ances and the cause of much trouble. Nearly every plant is attacked 

 and species considered of no economic importance may eventually 

 become pests to cultivated crops. It is no wonder, then, that so much 

 space is given for the consideration of these insects, and so many 

 apparently non-economic species are included in this work. 



The majority of the members of the family Coccidce have the ability 

 to produce a scale-like covering from which the common name is 

 derived, while some, unable to form a scale, have the epidermis hard- 

 ened into a thick, hard, chitinous wall, and still others secrete an 

 abundance of white poM r dery or cotton-like wax as a covering. The 

 scale, thickened epidermis and waxy covering are apparently for the 

 protection of the adults, eggs and young and prove so to a large 

 measure, and also enable the scale insects to resist to a marked degree 

 spraying and fumigation. 



The young are either born alive or hatch from eggs previous^ laid 

 by the female. In the first case the young hatch within the body of 

 the female from what corresponds to the egg, and in the latter case 

 the eggs are laid and hatch outside the body, in a shell or in a cottony 

 mass or sac secreted by the female for this purpose. The young 

 always have six legs, enabling them to move about freely. In many 

 genera the legs are retained throughout the entire life cycle, allowing 

 the adults to move as freely as the young, but in the scale-bearing 

 forms, and many others, the legs disappear in the females after the 

 first moult, there being nothing but the small body under the scale, 

 held in place by the proboscis and scale. 



The males at first resemble the young females, but soon after birth 

 make a tiny scale or cocoon in which transformation takes place, the 

 adults after the last moult emerging as very small, delicate, two- 

 winged insects with antennas and six legs, when the females are about 

 one third or full-grown. At this period mating takes place and the 

 males soon die. 



Nature of Work.— Scale insects feed by inserting into the tissues of 

 the plants (bark, fruit and leaves) their small beaks or mouth-parts 

 and sucking out the juices. As a consequence of their great numbers 

 and the removal of a large amount of juices, or a toxic effect produced 

 by the scales, the plants are often so weakened as to mature little 

 or no crops, or they may be entirely killed, while the fruits may be 

 deformed or rendered unsightly, and therefore unfit for market. 



Control.— The control of scale insects has long been one of great 

 importance throughout the entire country. Formerly only sprays 



