Family – Psyllidae

Pear psylla was introduced into Connecticut from Europe about 1832. It spread to the Northwest in 1939. Now it is common wherever pears are grown.

Egg: The eggs are yellowish orange and about 0.3 mm long. They are deposited in the creases of the bark, in old leaf scars and about the bases of the terminal buds. They are elongated and pear-shaped and have a smooth, shiny surface. A short stalk at the larger end attaches the egg to the bark, and a long, threadlike process projects from the smaller end.

Nymph: Small, yellow, wingless nymphs are about 3 mm long when newly hatched. There are five immature stages. The fifth instar nymph acquires wing pads.

Adult: Adults are dark reddish brown and have four wings.

The pear psylla is a pest of only pears and is present in all pear-growing areas of Canada and the United States.

The pear psylla secretes honeydew, which serves as a substratum for the growth of a black fungus that gives the tree a smoky, sooty appearance. Foliage may wilt and drop to the ground. Trees that are heavily infested for a long time produce little growth and set fewer fruit buds. Fruit remains undersized, fails to mature and may fall off the tree when only partly grown. The tree shows symptoms from "psylla shock" caused by the toxin the psylla have injected into it. Prolonged infestations may kill the tree outright.

The pear psylla has an unusual ability to develop resistance to chemical compounds.

The adults hibernate on the trunks, in crevices and under bark. When they are very abundant, they may collect under leaves and trash. On bright, sunny days near the end of March or in April, if the temperature is above 50 degrees F, the adults emerge from winter quarters. Most of the eggs are laid before the buds open. Eggs hatch in 11 to 30 days, depending on the temperature. Most of the eggs will have hatched by petal fall.

The nymphs migrate immediately to the axils of the leaf petioles and stems. If these places become crowded, they will scatter out to the undersides of the leaves and leaf petioles. They use their sucking mouthparts to feed on sap. The sap is changed in the body to honeydew and the honeydew is given off as droplets. Each nymph surrounds itself with a small puddle of smear of honeydew, which reflects light and flickers in the sunlight.

There are five immature stages. Nymphs get wing pads at the fifth molt. Three generations occur per year. The second and third generation of adults are smaller and lighter colored than those of the first generation. The females of later generations do not lay eggs on bark but deposit them along the midrib on the leaf undersides of place them in the notches at the edges of the leaves. Overwintering adults are produced in the fall.

In the prebloom period, use beating tray early in the morning to sample adults. Construct trays from aluminum screening, making an 18 inch square frame covered with white cloth. You can dislodge and collect adult pear psylla by tapping a limb with a rubber hose and holding the tray underneath the limb. Yellow, sticky traps used for monitoring apple maggot and cherry fruit fly can also be used to monitor overwintering pear psylla adults very early in the spring.

Pear psylla can develop resistance to chemicals quickly. The prognosis for continued chemical control of this pest is uncertain because the limited size of the crop does not warrant large expenditures to develop a pesticide to control this insect. Because pears are the only host of pear psylla, to ensure population in an orchard is treated with each spray. The pear psylla population is thus subjected to great selection pressure with little chance of dilution of the gene pool. This hastens the development of resistance.

Because they tend to fly considerable distances, a few scattered infestations can become a general infestation in a short time. Few parasites and predators exist, so control depends almost entirely on insecticides. Timing is important because the hard shell makes the adult stage and the fifth instar hard to control. The chances of reinfestation are very great because overwintering adults fly considerable distances in the fall and spring.

Pruning water sprouts around mid-July can greatly reduce populations because nymphs find it difficult to feed on old, hardened-off leaves.