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The redheaded pine sawfly is probably the most serious pest of red pine plantations in southern and central Ontario and south-central Quebec. A complete defoliation kills small trees, but less extensive feeding results in poor diameter growth and often the death of defoliated branches. Although red pine (Pinus resinosa [Ait.]) is the preferred host tree, jack (P. banksiana Lamb.), Scots (P. sylvestris L.) and other pines are attacked as well. Adults emerge and eggs are laid in the needles in June and July. The larvae may be found from July to early October feeding in colonies and show a preference for needles of the previous year's growth, although in heavy infestations all needles are consumed.

Extensive mortality of pine sometimes occurs in young plantations in spite of a host of natural controls such as parasitic insects; insect, bird and rodent predators; and virulent disease organisms, especially a polyhedral virus that often causes the collapse of heavy infestations. If necessary, a contact or stomach poison may be applied when the larvae are first seen to prevent serious loss of foliage.

Points of interest

• a full-grown larva is about 25 mm long
• winter is passed in a cocoon in the litter

References

Rose, A.H.; Lindquist, O.H.; Nystrom, K.L. 1999. Insects of Eastern Pines. Natural Resources Canada, Canadian Forest Service, Headquarters, Science Branch, Ottawa. ISBN 0-660-17720-X.