Rate responses of Lyonetia speculella Clem. (Lepidoptera:Lyonetiidae) to abamectin on non-bearing, apple trees

30 Pages·1993·5.2 MB·English

by  Schmitt, J. J

Historic, Archive Document
Do not assume content reflects current
scientific knowledge, policies, or practices.
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Rate responses of Lyonetia speculella Clem.
(Lepidoptera: Lyonetiidae) to
Abamectin on Non-Bearing, Apple Trees
J.J. Schmitt, M.W. Brown,
USDA-ARS, Appalachian Fruit Res. Sta., Kearneysville, WV, 25430,
and D.L. Cox,
Merck, Sharpe, and Dohme Res. Lab., Three Bridges, NJ, 08887
Introduction
Lyonetia speculella, a leafminer, disrupts photosynthesis in leaves of
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are sufficient older leaves to provide photosynthate.
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populations increasing at the end of the growing season.
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the same leaf.
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Materials and Methods
Branch terminals of newly planted, nonbearing, apple trees ('Empire',
"Golden Delicious', 'Liberty', and 'Priscilla') were studied from 5 August to
25 October when leafminers were abundant. Terminals were surveyed and chosen
for testing when at least one leaf possessed either & linear or 3 blotch
mines. An attempt was made to choose control terminala from the same tree.
When it was difficult to find trees with adequate populations of leafminers
terminals of adjacent trees were chosen normally within the same row.
Leaves were individually checked and the number of individuals of
leafminers within each life stage was recorded. The leaf with the most
abundant number of leafminers was marked with a twist-tie to be used as a
frame of reference for follow-up surveys.
Prior to treatment, natural enemies observed on the terminals were
removed and sleeves made of no-see-um netting were placed over the terminals
to prevent reinvasion of natural enemies. Treatment concentrations of
abamectin ranged from 16 to 0.5 ppm. Application consisted of dipping the
leaves in a half pint ball jar containing the different concentrations. The
corresponding terminal marked as control was dipped in water. After treatment
the sleeves were resecured.
Terminals were checked between 2 and 5 days, 7 to 10 days, and 14 days
after treatment at which time the number of individuals in each life stage
were counted. Eggs were not counted after 7 days since preliminary studies
indicated that hatch should occur within a week at the experimental
temperatures.
Probit analysis was conducted to determine significant relationships
between dose and mortality at different time periods and to estimate LDSO and
LD95 concentrations.
Results and Discussion
Figures 1-7 illustrate the effect of the different concentrations on
the leafminer over time. At 16 and 8 ppm there was 100% mortality before the
first week (Figures 1 and 2). At 4 and 3 ppm there was survivorship at the 2
week check (Figures 3 and 4). Interestingly, development was not as rapid as
indicated by the proportion of leafminers in the pupal stage after 7 days in
the control versus the treated terminals. Development to the pupal stage
during the 4 ppm test was probably due to inadequate treatment coverage.
With the 2 ppm treatment 100% mortality occurred prior to the two week
check. Although dissimilar to what had occurred at the 4 and 3 ppm treatment,
a lag time in development still existed with the greater proportion of
leafminers in linear mines after 14 days for the treatment as compared to the
pupal stage for the control (Figure 5). Further complicatinthgi s information
was the difficulty encountered in determining whether larvae in linear mines
were alive. Not until concentrations decrease to 1 or 0.5 ppm is there
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It is difficult to determine the effect Abamectin on eggs. However,
there was 39% reduction in egg viability on the treated terminals as compared
to 26% on the control terminals.
Percent reduction of each treatment over time is presented In Table 1.
The asterisks indicate data that does not Incorporate all the initial
individuals. Points of interest Include the amount of mortality caused by the
lower concentrations. As previously stated, although development rate was
similar to the control there was still a reduction in survivorship In the two
treatments. Another point of interest is the relatively high mortality of the
controls for the 2 and 3 ppm treatments.
LC5O and LC95 estimates are presented in Table 2. There was high
control mortality and much variability in the data. Of the many factors that
are important in selection of this compound the determination of the threshold
level and cost of the product. In other words, the attributes of such a
compound allows us to be concerned only with other factors besides
degradability and effectiveness. It is worthy of note that the application
method used here would probably be more effective than the normal spray
procedures and practices.
With respect to the damage tolerance, it would be nice to be able to
use a lower concentration to eliminate 95% of the pest in 14 days. However,
too much damage might have occurred. Although precise information was not
obtained during this experiment, previous studies indicate that a conservative
developmental estimate for the larval stages of L. speculella in the field
under a temperature range of 5-30 C is 14 days (Schmitt, unpublished). It is
this particular life stage that most damage occurs and therefore it would be
unwise to use a time frame much longer than even 7-10 days to achieve desired
mortality.
Timing of spray is also an important consideration. Although eggs have
been observed as early as mid-March, the recommendation is to spray as late as
possible - only when needed. Drought or natural enemies may develop early in
the season to curtail a large late season population, especially with an
insect like this that has a high Economic Injury Threshold (even though we
don't know what it is).
In conclusion, abamectin is a very effective compound on L.
speculella. More information regarding effects on natural enemies and other
pests, and field spray applications are necessary prior to implementation is
needed.
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