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AN
ECOLOGICAL STUDY OF SOME FOLIAGE-FEEDING INSECTS ON YOUNG
NONBEARING APPLE TREES IN WISCONSIN Erich Fred Legner. Ph.D. The University of Wisconsin, 1961 Supervisor: Professor
Earl R. Oatman An investigation into the ecology of
foliage-feeding insects was made in a young, nonbearing apple orchard in Door
County, Wisconsin. Two applications of a systemic aphicide were applied to one-half
the orchard in 1959. Interactions
were studied of an apple aphid, Aphis pomi DeGeer, population with
three primary destructive folliage-feeding insects: the eye-spotted bud moth,
Spilonota ocellana D. & S., fruit-tree leaf roller, Archips
argyrospilus (Walk.), and red -banded leaf roller, Argyrotaenia
velutinana (Walk.). Seventeen
species in nine families of Lepidoptera were collected from the orchard in
1959 and 33 species in 19 families in 1960.
Four species occurred in two generations; all others had a single
generation. The years 1959 and 1960 were phenologically similar; however,
tree variety, treatment and years significantly influenced the number of
individuals and species present, the Red Delicious and check sections
averaging the highest counts.
Terminal shoot growth, trunk diameter, and tree volume averaged
greater in the treated half of the orchard. Six
parasitic hymenopterous species were reared from the
eye-spotted bud moth, three of which were recorded for the first time from
this insect; two species from the fruit -tree leaf roller, one being
described for the first time; and a single species from the red-banded leaf
roller, which was common to this host. Parasitism of the eye-spotted bud moth was
2.9 percent in 1959 and 8.8 percent in 1960; of the fruit-tree leaf roller 21.4 percent
in 1959 and 32.4 percent in 1960; and of the red-banded leaf roller three
percent in 1960. Apple aphid predators included nine coccinellid, three
syrphid, five chrysopid and two hemerobiid species. Four
pathogenic agents and a suspected virus caused 3.4 percent mortality of
eye-spotted bud moth spring larvae and 0.1 percent mortality of summer larvae
in 1960. Survival in the orchard from
September 1959 to June 1960 averaged 87 percent for this species. Over
wintering mortality of red -banded leaf roller pupae held in cages was 12.5
percent in 1959-1960. Pupal
mortality was the primary factor in natural control of the eye-spotted bud
moth and fruit-tree leaf roller. It
was similar for the eye-spotted bud moth in both years and in all orchard
sections, averaging 22 percent from larval collections and 77 percent from pupal
collections. Cessation of
terminal growth was apparently the primary factor in
reducing the apple aphid population. Nests
constructed on twigs were primary and in leaves were secondary sites of
pupation for the eye-spotted bud moth.
Pupation occurred earlier on Red Delicious than on Cortland. Choice of eye-spotted bud moth pupation
sites in an orchard tree were at random, and the percent of summer larvae in
nests was the same for all tree levels. the southwest quadrant of trees
contained significantly fewer eye-spotted bud moth nests in the last half of
September 1960, greater numbers being found in the top and northeast quadrant
of trees. There was no correlation between tree size and total number of eye
-spotted bud moth larvae and pupae per tree. The 100-leaf sample was statistically
adequate to estimate the percent of summer eye-spotted bud moth larvae which
occurred in their nests on any given date.
Activity of spring eye-spotted bud moth larvae decreased as their age
increased; their gregarious nature was also demonstrated. The sex
ratio for the eye -spotted bud moth changed from a 1:1 ratio early in the
emergence period to a 2.4 to l.0 ratio in favor of females at the close of
this period. Physical
factors later in the season were apparently more favorable for eye-spotted
bud moth development. Warm
temperatures and moderate rainfall in May and June of 1959 apparently favored
a build up of the apple aphid population. Low temperatures and high rainfall
during these months in 1960 apparently had an adverse effect on the apple
aphids which halted their development. |