Question: Round growth are occurring on the leaf petioles of several cottonwood trees around my home. What is causing this and is it harmful to the trees?
Answer: The round growths that are occurring on your trees are the home of a petiole gall forming aphid, with a scientific name of Pemphigus populicaulis. These aphids induce globose galls on the leaf petiole of cottonwood and other poplar species. No leaf blade distortion occurs from the gall formation. Cutting open the galls will reveal the aphids. The life cycle of these insects takes place in one year. Eggs, the product of sexual union, are laid in autumn in crevices of the bark. They hatch in spring, and nymphs feed on newly developing leaf petioles. In a few days the up folding of gall tissue completely encloses the stationary stem mother. Birth of young is parthenogenically (meaning cloned) while confined inside the gall in a hollow chamber. These young, when mature, have wings. During midsummer a slit-like orifice develops, allowing the winged aphids to escape and fly to the roots of secondary host plants in the Crucifer or Composite family where they produce several generations. In late summer winged aphids that developed on the secondary host plants fly back to the primary host, cottonwood trees. Mating occurs and the female lays the eggs that overwinter.
Control: Because the gall-forming aphids do little damage to the affected tree control measures are not recommended.
Source: Insects That Feed on Trees and Shrubs. 1991. Warren T. Johnson and Howard H. Lyon. Cornell University Press, Ithaca, NY. pp.461-462.
Question: Several insects have been feeding and mating on my plants. They are olive/brown in color and look like an elongated beetle. Their legs are very long. What are these and how can I control them?
Answer: The insect is the rose chafer (Macrodactylus subspinosus (Fabr.)) These are general feeder although it is associated with roses and grapes. Feeding also occurs on raspberry, blackberry, strawberry, peony, iris, dahlia, hollyhock, and other ornamental flowers and shrubs. This pest is abundant in areas having light, sandy soil. The beetle feeds on flowers, leaves, fruits and the larvae feed in the soil on roots of various grasses and weeds. The larvae are small white grubs that pass the winter deep in the soil and migrate upward in the spring. They pupate in late April and emerge as long legged adults in May and early June. Feeding and mating occur, sometimes simultaneously, in June and July, the eggs being deposited singly a few inches below the soil surface. Hatching takes place in two weeks and feed until cold weather approached, being nearly full grown. They then begin migrating down into the soil to avoid cold weather. One generation occurs per year.
Control: Any insecticide whether "organic" or conventional will destroy the adults while they feed if they occur in large numbers. Many years there is a limited population and limited damage. With many insects cold winters decrease their population. Cold weather, however will not eradicate insects. The past few winters in Cochise County have been fairly mild allowing increase insect populations to survive and produce.
Source: Insect Pests of Farm, Garden, and Orchard. 7th Edition. 1979. Ralph H. Davidson and William F. Lyon. John Wiley & Sons, New York. pp. 436.