Farm Forestry New Zealand

PESTS AND DISEASES OF FORESTRY IN NEW ZEALAND

Spruce Aphid, Elatobium abietinum

Scion is the leading provider of forest-related knowledge in New Zealand
Formerly known as the Forest Research Institute, Scion has been a leader in research relating to forest health for over 50 years. The Rotorua-based Crown Research Institute continues to provide science that will protect all forests from damage caused by insect pests, pathogens and weeds. The information presented below arises from these research activities.

Forest and Timber Insects in New Zealand No. 54: Spruce aphid.

Revised 2009
Based on R. Zondag (1983)
 

Insect: Elatobium abietinum (Walker) (Hemiptera: Aphididae) *

* One other aphid, Cinara pilicornis (Hartig), is present on spruce in New Zealand. This aphid is slightly larger than the spruce aphid and has a plump, dull brown body. It seems to have little effect on the tree.


Fig. 1 - Foliage of sitka spruce attacked by spruce aphid.
 

Type of injury
Yellow spots, which eventually turn brown, develop on needles where spruce aphids have been sucking sap (Fig.1). Needles with several spots eventually die and fall off. Extreme defoliation follows severe attack and susceptible trees may die. New needles on trees infested for several years are usually shorter in length than normal. (Browning and loss of new foliage is not caused by the aphid but is the result of feeding by the spruce mite, Oligonychus ununguis (Jacobi). Since both aphids and mites occur on the same tree it is difficult to say which causes the most damage, but as the aphid is present only on the older needles, attack by the mite on recent growth must contribute considerably to tree debility and death.)

Hosts
This aphid attacks only Picea (spruce). In New Zealand it occurs on many species of spruce, including P. abies (Norway spruce) and P. sitchensis (Sitka spruce) which are the most commonly planted.

Distribution
This accidentally introduced insect was first collected in New Zealand in 1920, and is present throughout the country. Although its geographical origin is unknown, the insect occurs in Europe and western North America.

Economic importance
Some early spruce plantings have grown satisfactorily but many have failed. Defoliation by spruce aphid (and spruce mite) has been one of the main causes of the failure, but other constraints include phosphate deficiency in the soil, possible absence of the right sort of mycorrhizal fungi, and lack of sites suitable for good growth. These problems prevent spruce being seriously considered for plantation forestry. However, in recent years interest has been expressed in the use of Sitka spruce as a secondary species for some situations in certain parts of the South Island, and experimental plantings have been made.

Description, life history, and habits
This green, rather rotund aphid can be up to 1.7 mm long. It has small black spots on its upper surface and a pair of spike-like tubes (or cornices) projecting backwards from the abdomen. The adults (Fig. 2 and 3) may be winged or wingless, but an intermediate form with aborted wings is occasionally found. The population is wholly female, and the young are born alive.


Fig. 2 - Winged adult spruce aphid. Actual length 1.75 mm.



Fig. 3 - Wingless adult spruce aphid. Actual length 1.5 mm.
 

Wingless adults give birth all year round, even when temperatures are below freezing. They produce an average of 33 young, with 69 being the maximum recorded. The rate of reproduction during the winter is only slightly lower than that during the summer, but the length of pre-adult life and the age of the adult before it gives birth are increased. Wingless adults live an average of 50 days, although a lifespan of 120 days has been recorded. The length of adult life decreases as the temperature increases.

Most of the young develop into wingless adults which reach maturity 18-38 days after birth. In early July the proportion of winged forms starts to increase, with most appearing about the end of October and beginning of November. It is these fully winged insects which are responsible for spreading infestations from tree to tree. In one experiment the winged forms lived for an average of 12 days.

The aphids feed by inserting their stylet mouthparts through the stomata (naturally occurring minute openings) in the surface of the needles and penetrating the underlying cells to extract the plant juices; they prefer second and third year foliage. They are usually found on the underside of the oldest needles of an infested shoot, and tend to be concentrated on the lower shaded portions of the crown of the tree. The amount of defoliation increases with the density of the aphid population, and results from the amount of sap removed, or saliva injected, or epidermis damaged rather than from any disease which could conceivably have been transmitted.

Spruce aphids are most numerous in spring and early summer, with few being found during the remainder of summer or in autumn, possibly because predatory insects become more effective at these times since damaged foliage has been cast and fewer needles have to be searched. Starvation may also reduce aphid populations during the summer once the older foliage has been shed.

Observations in Europe have shown that:

• The nutritional value of sap, which is greater in spring than midsummer, is of considerable importance in regulating spruce aphid numbers; 
• Heavy rain and strong winds do not remove many spruce aphids from needles;
• Severe minimum temperatures (-7°C or lower) or prolonged periods below 6°C can cause considerable mortality amongst spruce aphids.

Control
Valuable ornamental specimen trees can be sprayed with an insecticide suitable for controlling sapsucking insects, but treatment may have to be repeated because of reinfestation from other trees.

In New Zealand the larvae of the lacewings Drepanacra binocula (Newman) and Micromus tasmaniae (Walker) (Hemerobiidae), and the hoverflies Melanostoma fasciatum (Macquart) and Syrphus novaezealandiae Macquart (Syrphidae) feed on the spruce aphid. Adults and larvae of the two-spotted ladybird Adalia bipunctata (L.), and the eleven-spotted ladybird Coccinella undecimpunctata L. also prey on this aphid.

Bibliography
Bejer-Petersen, B. 1962: Peak years and the regulation of numbers in the aphid Neomyzaphis abietina Walker. Oikos 13: 155-168.
Dumbleton, R.J. 1932: Report on spruce-aphid investigation for the year ending December 1930. New Zealand Journal of Science and Technology 13: 207-220.
Hussey, N.W. 1952: A contribution to the bionomics of the green spruce aphid (Neomyzaphis abietina Walker). Scottish Forestry 6: 121-130.
Zondag, R. 1983: Elatobium abietinum (Walker) (Hemiptera: Aphididae). Spruce aphid. New Zealand Forest Service, Forest and Timber Insects in New Zealand No. 54.

 

This information is intended for general interest only. It is not intended to be a substitute for specific specialist advice on any matter and should not be relied on for that purpose. Scion will not be liable for any direct, indirect, incidental, special, consequential or exemplary damages, loss of profits, or any other intangible losses that result from using the information provided on this site.
(Scion is the trading name of the New Zealand Forest Research Institute Limited.)