Fruit Insect Focus for September, 1997
Lyonetia Leafminer Lyonetia prunifoliella (Hubner)
I. Introduction: Although first reported from apple in the 1920s,
this is a relatively new pest on apple in the mid-Atlantic region, first noticed as a
common leafminer in the early 1980s in Virginia and West Virginia. Mining activity is
restricted to young leaves; it is therefore more common on young, non-bearing trees since
more leaves are succulent and vigorous.
II. Hosts: Apple, plum, cherry, birch and grape.
III. Description: Adults are about the same size as the moths of spotted tentiform leafminer, but are predominantly silver-gray with white bands on the wings (photo 1-55). There is a tuft of upward-projecting scales on the top of the head. Larvae are pale green and about 3/16 inch (5 mm) long when mature. Pupae are pale green initially, and become dark purple as adult emergence nears.
IV. Biology: The life history of this species
is poorly known and is the subject of research in West Virginia. The leafminer overwinters
in the adult stage. Eggs are laid in the undersides of expanding leaves. Mines begin as
narrow, winding, serpentine paths that turn into broad, irregular brown blotches. Clumps
of black frass may be seen hanging from holes in the mines. Larvae may leave the mine and
start a new mine, sometimes on a different leaf, by descending on a strand of silk. This
is important since more than 
60 mines may be
initiated in a single leaf; successful development of this many larvae in one leaf is
unlikely. Larvae leave the mine for pupation, which occurs in a silken "hammock"
spun by the larva on the underside of a lower leaf (photo 1-56). There are six to
eight generations per season, the first beginning in mid to late March. The first
generation is usually in very low densities due to high mortality of overwintering adults.
Development from egg to adult may occur in as few as 20 days at 71.6 to 78.8 F (22-26 C).
By midsummer, there is considerable overlap of generations and all life stages may be
found at any time.
V. Injury: Mines are the most visible evidence
of this species (photo 1-57). Several mines may overlap on a leaf, turning the
whole leaf brown. Most injury occurs 
from midsummer until early fall when trees respond to rainfall with
a new flush of growth, and this insect may be a problem on non-bearing trees where a great
proportion of leaves are susceptible to attack.
VI. Monitoring: Examine young leaves of apple, especially on non-bearing trees, for the presence of mines (photo 1-57). No thresholds are currently available.
VII. Management: This insect is not likely to require control on mature bearing trees. Control may be necessary on non-bearing trees, or on dwarf trees under irrigation which results in a higher proportion of young leaves that are susceptible to attack. Provado or Vydate is recommended where control is needed.
