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Pests and diseases of forestry in New Zealand



 Spruce Aphid (Elatobium abietinum) in New Zealand





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.
  




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