arrowhead scale

Unaspis yanonensis Kuwana

Arrowhead scale is considered native to China but has invaded and spread though much of Japan, France, and Italy. It is not known to occur in the U.S. Infested live plants or fruit provide the main method of introduction to other localities. Hosts include all citrus, especially oranges, but also a wide range of other crops, including bananas, coconuts, guavas, hibiscus, jackfruits, kumquats, and pineapples. The eggs of the first generation are laid under the armor of the adult female. The orange-yellow egg is entirely smooth and oval. In citrus-producing areas of the United States, egg laying will most likely begin in February or March with each female producing about 200 eggs. The first larval stage (crawler) is an active, flat, oval-shaped, pale-yellow creature with purple eyes. After the first molt the legs are lost and the antennae are reduced to a single segment. The body of the adult female does not change much from this form. Male nymphs have a pre-pupal stage leading to a winged adult. The prepupa is orange-yellow with dark purple-brown eyes. The rudimentary antennae, legs, and wings are visible. The winged male is orange-yellow with deep dark brownish-purple eyes and is 1/16 of an inch long. A light brown band can be seen across the thorax. The abdomen narrows at the end and has a sharp style. Female scale covers are mussel-shell shaped 1/8 of an inch, slightly convex, blackish-brown with a paler margin. The scale cover of the male is smaller than that of the female, white, and elongate oval in shape. There are 2 to 4 generations per year and development is strongly influenced by air temperatures. Feeding of the insect produces chlorotic-necrotic spots, irregular growth, and limb die-back, as well as malformation of fruit and premature drop.