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Pest status
Chapter 50
Coleophora serratelfa (L.), Birch Casebearer
(Lepidoptera: Coleophoridae)
A.G. RASKE
The birch casebearer, Co/eophora semlIe/JQ (L.)I, is native to Europe; Salman (1929)
postulated that the insect was accidentally introduced into northeastern North America
about 1920. There it has become the most important defoliator of white birch, Betula
papyri/era Marsh. It was discovered in Maine in 1927 (Salman 1929) and had spread to
New Brunswick by 1933, to Nova Scotia by 1937 (Reeks 1951), to Ontario by 1944
(Raizenne 1952), to Prince Edward Island by 1951, to Quebec by 1956, and to Manitoba
by 1969 (Cochran 1974). It was discovered in western Newfoundland in 1953 and had
spread throughout the island by 1971 (Raske 1974a). It was discovered in Victoria,
British Columbia, in 1962 (probably from a separate introduction) and was causing
severe defoliation of ornamental trees in about 100 ha of the city by 1980 (van Sickle
personal communication). The pest has also been collected in Alberta (B. Wright 1981,
personal communication). This casebearer thus appears to occur throughout Canada
(Fig. 11) but the exact distribution in central and western Canada is largely unknown.
Identification records for Ontario were recently revised. Thus C. serratella has never
been positively identified in Ontario but a thorough search has not been undertaken.
The most common form of damage to trees is the browning and reduction of foliage
caused by the feeding of late instar larvae in early summer (Bryant & Raske 1975). The
larva feeds like a leafminer. It attaches its case to a leaf and mines as far as it can reach
without leaving the case, creating somewhat rectangular mined patches. After a larva
has eaten all the food within reach, it moves to another part of the leaf and repeats the
process. The mined portion turns brown and this causes the scorched appearance of
severely damaged trees. The damage tends to become masked later in the summer by the
continuous production of new foliage.
The more severe form of damage occurs in early spring when large numbers of earlyinstar
larvae destroy the flushing buds, causing twig, branch, and sometimes tree
mortality (Bryant & Raske 1975); many insects starve.
Outbreaks of the birch casebearer have been reported from Victoria, British Columbia,
and from Quebec to Newfoundland. The insect probably reached St. John's, Newfoundland,
in the late 1960s. It was extremely rare in Newfoundland in 1971 (Raske 19740) but
had reached outbreak proportions by 1980. In a newly invaded area, populations tend to
increase to a super-saturation level. After 1 or 2 years populations decline but continue
to cause a high level of chronic defoliation of 20-50%. However, the post-outbreak
population levels vary in both location and time.
The life history and habits of the birch case bearer in the northeastern United States
were reported by Salman (1929) and by Gillespie (1932). Guevremont & Juillet (1974)
and Raske (1976) described aspects of the life history in Canada. Cosh an (1974) and
Gepp (1975a) have summarized life history studies in Europe. The life cycle ofthe insect
spans two calendar years. In Canada, eggs are laid in July on the underside of leaves.
Larvae hatch in August and mine the leaf until early September. After moulting they
cut a case from the leaf epidermis, crawl to a different area of the leaf, and feed until fall.
I J.C. Bradley (In: Kloet, G.S.; Hinks, W.D. (Ells.) 1972 - Handbook for the identification
of British insects, Vol. 2, Part 2. Lepidoptera. Royal Entomological Society,
London) cites C. fuscedinella Zell. as a synonym of C. serralella (L.).
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