GARDEN SYMPHYLAN LIFE CYCLE AND HABITS
The Garden Symphylan, Scutigerella immaculata, is primarily a pest of mint
in western Oregon and Washington, but may occur in other production areas.
Mature symphylans are 1/8 to 1/4 inch long, white, soft-bodied, centipede-like
animals, with prominent, many-segmented antennae. They move very rapidly
when disturbed, vigorously vibrating their antennae. Symphylans are not true
insects, since they possess 12 rather than 3 pairs of legs in the adult stage.
However, newly hatched nymphs have only six pairs of legs. An additional pair
of legs is added at each molt, until the adult stage is reached.
Eggs, nymphs, and adults can be found in any month of the year. Peak egg
laying occurs primarily during the early spring months with another, smaller
peak in the fall. Nymphs and adults are active in the late winter and spring.
They are found in increasing numbers in the upper 6 to 8 inches of soil from
about April through August. Eggs are deposited in clusters of 4 to 25 at various
depths, depending on soil temperature, moisture, and soil structure. Eggs are
covered with a network of tiny ridges and white when first laid. They gradually
turn light tan in color. Eggs hatch in 30 to 40 days and nymphs feed on small
roots and root hairs. The total developmental time from egg to adult requires
about 5 months at 10oC. Nymphs and adults move freely in the soil and seek
depths where favorable temperature and moisture occur. Cold temperatures
during the fall and winter and extreme dryness in the summer cause them to
migrate deep in the soil. There are one to two generations per year. For
additional information see Berry and Robinson (1974), Biology and Control of
the Garden Symphylan, Oregon State University Extension Circular No. 845.
MANAGEMENT AND CONTROL OF GARDEN SYMPHYLAN
If soil moisture is adequate, the garden symphylan can be observed in mint root
borer soil samples. However, postharvest samples for mint root borer are
usually too shallow to detect a significant symphylan population. In the fall, this
is because of the dry soil profile, a natural seasonal reduction in population,
and the symphylan's tendency to travel downward in the soil to avoid high
temperatures or seek moisture.
The best time of year to sample for symphylans is from March through
September. However, to properly control them with an insecticide, you must
apply it prior to spring regrowth. Take a square foot soil sample to a depth of 10
inches from several different sites in the field (one site per 1 1/2 acres). Count
the number of symphylans per sample and calculate an average number per
sample. If an average of four to five symphylans is found in the samples, control
may be required depending on the vigor of the stand.
A parasitoid mite predator, Pergamasus quisquiliarum, commonly occurs in
western Oregon soils (Berry, 1973). The developmental period of this predator
requires about 17 days, compared to about 87 days for the garden symphylan
at 20oC. Therefore, this predator could complete about five generations to one
generation of the symphylan at this temperature. Studies have shown that this
predator may consume up to 12 symphylans during one generation, indicating
that it could be an important factor in regulating symphylan populations.
If treatment is justified, apply Dyfonate and incorporate it by irrigation (see the
insecticide table for rates to apply). Apply Dyfonate at least 3 weeks before
Sinbar applications. If possible, identify areas in the field where the population
is concentrated and treat only those areas. Symphylans prefer heavier soils to
sandy soils and often infest ridge or high areas, avoiding low spots where water
concentrates. If possible, incorporate Dyfonate into the soil by tillage,
particularly in new plantings of mint. For additional information about control of
the Garden Symphylan, see Berry and Robinson (1974).
Garden Symphylan Life Cycle/Habits