Aphid and Adelgid Pests of Conifers in Oregon J.D
EC 1444 • November 1994 75¢
Aphid and Adelgid Pests of Conifers in Oregon J.D. DeAngelis
his publication covers the Aphids are small, soft-bodied Aphid and adelgid life history important aphid and insects that suck plant sap from can be extremely complex, often adelgid pests of conifers in their hosts. Toxic or growth- involving more than one host TOregon, excluding those that regulating chemicals often are plant. Typically, there are several primarily feed on the roots of injected at the same time. parthenogenetic (asexual) genera- their host. Adelgids are closely related tions each year. The final genera- Conifers are plants that bear to aphids but are distinguished tion before winter may be cones as reproductive structures. from their better-known rela- sexual, and winter usually is Examples are pine, fir, spruce, tives because they feed only on spent in the egg stage. hemlock, Douglas-fir, and cedar. conifers, while aphids have host Many aphids and adelgids Aphids and adelgids can be plants in all plant families. secrete a white, waxy covering important pests in Christmas Adelgids currently are placed in from pores on the body. The wax tree plantations, conifer nurser- their own family, Adelgidae, provides protection against ies, and landscape plantings. The while aphids belong to the Identification Key lists the tree family Aphididae. Both families Jack D. DeAngelis, Extension species included in this publica- belong to the large and diverse entomologist, Oregon State tion and their pests. insect order Homoptera. University.
Most Common Aphid and Adelgid Pests by Host Tree
Tree Pests
Douglas-fir (Pseudotsuga) Cooley spruce gall adelgid (secondary host; can reach pest status) conifer aphids (Cinara sp.)
Grand fir (Abies grandis) balsam twig aphid (Mindarus abietinus) conifer aphids (Cinara sp.) balsam woolly adelgid (Adelges piceae)
Noble fir (Abies nobilis) conifer aphids (Cinara sp.) balsam woolly adelgid (Adelges piceae)
Pine (Pinus) conifer aphids (Cinara sp.) pine bark adelgid (Pineus strobi)
Spruce (Picea) conifer aphids (Cinara sp.) spruce aphid (Elatobium abietinum) Cooley spruce gall adelgid (primary host; usually not a pest) Identification Key Important Aphid and Adelgid Pests of Northwest Conifers by Host Tree Tree and Symptoms Pests
DOUGLAS-FIR (Pseudotsuga) Aphids without much waxy covering. Produce large amounts of honeydew, which may be attractive to ants and yellow jackets or covered by sooty mold ...... conifer aphids (Cinara sp.) “Pepper” flecks (crawlers) on needles in late spring and/or white cottony tufts on needles before bud break or after about mid-June ...... Cooley spruce gall adelgid (Adelges cooleyi)
TRUE FIRS (Abies) Aphids without much waxy covering. Produce large amounts of honeydew, which may be attractive to ants and yellow jackets or covered by sooty mold ...... conifer aphids (Cinara sp.) Swelling (“gouting”) of branch nodes. Very small waxy adelgids may or may not be found. Trunk, branches, or twigs may be covered with white, waxy secretions in heavy infestations ...... balsam woolly adelgid (Adelges piceae) Twisting of new growth. Small greenish-yellow or bluish-gray aphids. Wax and honeydew may be present, causing needles to mat together ...... balsam twig aphid (Mindarus abietinus)
SPRUCE (Picea) Aphids without much waxy covering. Produce large amounts of honeydew, which may be attractive to ants and yellow jackets or covered by sooty mold ...... conifer aphids (Cinara sp.) Pineapple-shaped galls or cones on branch tips ...... Cooley spruce gall adelgid (Adelges cooleyi) Twisting of new growth. Small greenish-yellow or bluish-gray aphids. Wax and honeydew may be present as well ...... balsam twig aphid (Mindarus abietinus) Old (more than 1-year-old) needles shed, especially on lower, shaded portions of tree. Aphids peak in late winter (February–March), decline toward summer. Small, green aphids ...... spruce aphid (Elatobium abietinum)
PINE (Pinus) Aphids without much waxy covering. Produce large amounts of honeydew, which may be attractive to ants and yellow jackets or covered by sooty mold ...... conifer aphids (Cinara sp.) White flocking on bark of branches and trunk. Trunk may appear “snow covered” ...... pine bark adelgid (Pineus strobi)
HEMLOCK (Tsuga) Aphids without much waxy covering. Produce large amounts of honeydew, which may be attractive to ants and yellow jackets or covered by sooty mold ...... conifer aphids (Cinara sp.) Cottony tufts on bark and twigs. May seriously weaken ornamental trees ...... hemlock adelgid (Adelges tsugae)
2 water loss and predators. The When artificially presence or absence of wax injected, these substances often is a diagnostic feature can cause dramatic changes used for identification. in plant development. Aphid and adelgid identifica- Perhaps the best example is tion is difficult. The best place to the “pineapple” galls on start is with identification of the spruce that are formed by host tree since many of these growth hormones injected pests are specific to one type of by developing nymphs of host. Use the Identification Key as the Cooley spruce gall a starting point. adelgid. This pest is dis- cussed in greater detail Feeding habits and below. effects on host plants Life cycles Aphids and adelgids feed by Aphid and adelgid life piercing host tissue and with- cycles are so complex and drawing the plant’s sap through varied that we can make only straw-like mouthparts. This broad generalizations. For mode of feeding produces large example, in many species the amounts of honeydew—the feeding occurs on the secondary insect’s form changes depend- sticky, sugary liquid found host on needles or bark under a ing on host tree or season. below aphid or adelgid colonies. covering of wax. No galls are Reproduction can be complex Honeydew attracts ants, yellow formed on the secondary host. as well. At certain times of the jackets, and other scavengers Picea (spruce) normally is the year, no males are produced and and supports growth of a black primary host; and fir, larch, reproduction occurs asexually. fungus called sooty mold. Douglas-fir, hemlock, or pine is Even more strange, certain Aphids and adelgids feed on the secondary host. species sometimes give birth to needles, twigs, branches, trunks, live young and at other times and roots—in other words, lay eggs. virtually anywhere on the plant. Because these pests change However, each particular appearance from host to host species usually is confined to a Use pesticides safely! and season to season, it often is narrower range of feeding sites. better to identify aphids and • Wear protective clothing and While feeding, these pests adelgids based on the host tree. safety devices as recom- may inject toxins, growth- Generalized aphid life cycle. mended on the label. Bathe or regulating hormones, or plant Eggs overwinter on needles or shower after each use. pathogens into their host plant. bark. Young hatch in mid- Injection of plant toxins (tox- • Read the pesticide label— March, begin feeding, and emia) is observed most easily in even if you’ve used the develop into adults in April. broadleaf plants, where you pesticide before. Follow Several generations can be may find twisted, stunted closely the instructions on the produced during the warm growth above an aphid colony. label (and any other direc- months. Large colonies, often Plant viruses also can be trans- tions you have). attended by ants, develop on mitted between plants by aphid • Be cautious when you apply twigs and branches. These feeding, but this is not known to pesticides. Know your legal colonies produce copious occur in conifers. responsibility as a pesticide amounts of honeydew. Both Compounds that resemble applicator. You may be liable winged and wingless forms can natural plant growth hormones for injury or damage resulting be found in the same colony. are injected by some conifer- from pesticide use. Generalized adelgid life feeding aphids and adelgids cycle. The complete life cycle while they feed. These sub- takes 2 years and involves two stances mimic natural plant hosts, a primary host and a chemicals that regulate growth secondary host. A gall is pro- and reproduction. duced on the primary host, while
3 Pest descriptions make galls on spruce. It is, even after the adelgids them- however, the most common and selves are gone. Infestation Cooley spruce gall adelgid is the one that alternates with causes bud deformity, branch (Adelges cooleyi) has an ex- Douglas-fir. It also may persist die-back, and damage to parts tremely complex life cycle, part on Douglas-fir by reproducing of the outer bark. of which is spent on spruce parthenogenetically for many Severe infestations can leave while the other part is completed generations. the entire trunk covered with on Douglas-fir. The complete Balsam woolly adelgid waxy secretions. At this point, cycle may extend over 2 years (Adelges piceae) is a pest of true the tree may be beyond recov- and include several forms. firs only. The insect is not native ery. This insect is responsible for The most common form to this country, and only females destruction of many thousands occurs on Douglas-fir and have ever been detected. The of board feet of fir timber each appears as small, white, cottony 1 adults are less than ⁄25" long, year. tufts on the underside of wingless, and covered by dirty, Hemlock adelgid (Adelges needles. In some years, the white wax. tsugae) is a serious pest of adelgid is so numerous that the Because they are wingless, ornamental hemlock. This ground below large Douglas-fir their only means of dispersal is adelgid settles on twigs or at the trees is sticky with honeydew. by wind. They attack parts of base of needles and produces a The form of Cooley spruce the trunk and branches by white, waxy mass. Its feeding gall adelgid that feeds on spruce inserting their mouthparts deep causes premature needle drop produces a growth deformity or into the underlying tissue. and a general decline in tree gall that resembles a cone or When attacked, firs often vigor. The immature, or crawler, pineapple on branch tips. Galls develop a condition called stage occurs from late March to are not formed on the secondary “gouting,” in which the branch June. host, Douglas-fir. Unless the nodes swell. This deformity is Pine bark adelgid (Pineus infestation is severe, this insect is caused by a growth hormone or strobi), like many other adelgids, not considered a pest of spruce. toxin injected by the feeding feeds on the trunk and limbs of The Cooley spruce gall adelgids. The condition persists its host trees. Eastern white pine, adelgid is not the only adelgid to
Figure 1.—Pest calendar: Balsam twig aphid.
4 Scotch pine, and Austria pine because populations peak in late yellow jackets and may be can be severely infested. The winter. Damage normally is covered by sooty mold. immature stages may be present noticed before the insects are Important natural enemies are early in the year. Infestation first detected. ladybird beetles, lacewings, and occurs on the shaded portions of Infested trees shed older syrphid fly larvae. Artificial the trunk and limbs. needles, becoming thin or bare releases of ladybird beetles Balsam twig aphid (Mindarus on the inside—often producing (Hippodamia convergens) are not abietinus) has a complex life what is called a “bottle brush” effective, however. history. It has been collected on appearance. It may take 5 years Instead you should rely on alpine, balsam, Fraser, grand, and for the tree to recover its full natural populations of ladybirds. white fir; white and Colorado complement of foliage. Also, spot treating areas of spruce; and juniper. Overwin- Conifer aphids (Cinara sp.) infestation with insecticide or tered eggs hatch in spring. are the most common aphids insecticidal soap may reduce the Infestations result in needles found in conifers. There are need to treat whole fields. being twisted and matted about 175 species worldwide. together with copious amounts Conifer aphids do not have Control of honeydew and wax. The secondary hosts. They usually aphids may be either bluish- are found on twigs and Unfortunately, injury thresh- gray or yellowish. In Christmas branches but may occur on olds have not been established tree plantations, severe damage trunks and roots. Most feed in for aphid and adelgid pests in can require up to 2 to 3 years for groups; a few, however, are conifers. Your decision to treat, regrowth to repair. solitary. Several generations are either chemically or non-chemi- Spruce aphid (Elatobium produced each year, possibly cally, should take into account abietinum) is a particularly building to high levels by late several points. destructive pest of ornamental summer or early fall. First, how long is it until spruce. The aphid is very small Conifer aphids always are harvest? Trees destined for 1 1 harvest this year may require ( ⁄25" – ⁄16" long) and is green. associated with honeydew, Discovery is difficult because of which is attractive to ants and more attention than trees that are the insect’s small size and 2 or more years from harvest.
Figure 2.—Pest calendar: Balsam woolly adelgid.
5 Second, consider the presence PNW Insect Control Handbook, Pest calendars of natural enemies and expected revised annually by the Exten- weather conditions. Artificial sion Services of Oregon State The pest calendars in this control might be more important University, Washington State publication are intended to if natural enemies are scarce and University, and the University of assist you in recognizing aphid the weather is hot and dry than Idaho. The Handbook contains and adelgid pest problems. Each if natural enemies are common sections on both Christmas Tree calendar has three “event lines.” and the weather is cool and wet. Plantation Pests and Ornamen- The top line indicates the best Also consider how much of tal Plants where you will find time to observe damage symp- the field you need to treat. It information concerning pests of toms, the middle line when to may be better in the long run to conifers. To order, send $19.50 to monitor or scout for the pest, spot-treat a few heavily infested Publications Orders, Extension and the bottom line when to trees rather than waste money and Experiment Station Com- apply control measures, if treating a whole field and risk munications, Oregon State needed. Do not rely only on disrupting the natural enemy University, Administrative these calendars when making complex. Services A422, Corvallis, OR pest control decisions—use For specific suggestions, 97331-2119. (541) 737-2513. them only as a guide. consult the latest edition of the
Figure 3.—Pest calendar: Conifer aphid.
6 Figure 4.—Pest calendar: Cooley spruce gall adelgid.
Figure 5.—Pest calendar: Spruce aphid.
7 Since pesticide registrations change frequently, resulting in more or fewer available pesticides and changes in permissible pesticide practices, this publication doesn’t make specific pesticide recommendations. For current recommendations, refer to the Pacific Northwest Insect Control Handbook, published and revised annually by the Extension Services of Oregon State University, Washington State University, and the University of Idaho. In addition, detailed instructions for pesticide use are provided on pesticide container labels and in other literature provided by pesticide manufacturers. This publication was produced and distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Extension work is a cooperative program of Oregon State University, the U.S. Department of Agriculture, and Oregon counties. Oregon State University Extension Service offers educational programs, activities, and materials—without regard to race, color, religion, sex, sexual orientation, national origin, age, marital status, disability, and disabled veteran or Vietnam-era veteran status—as required by Title VI of the Civil Rights Act of 1964, Title IX of the Education Amendments of 1972, and Section 504 of the Rehabilitation Act of 1973. Oregon State University Extension Service is an Equal Opportunity Employer.