|Abstract or Summary
- The life history, temperature, humidity, and feeding requirements of the
phytoseiid predator mite, Typhlodromus americanus Chant and Yoshida-Shaul were
tested in the laboratory. Occurance of the mite in the field during different times of the
year was investigated as well. Effects of temperature and humidity on egg hatch, the
feeding requirements of the larvae, the amount consumed by each life stage, the length of
each life stage and suitability of different food sources were investigated in the
laboratory. The use of the mite as a biological control agent was evaluated by using the
information gained from the laboratory experiments.
T. americanus was originally discovered in plantation grown Douglas-fir in
western Oregon. Since that time the mite has been found on a number of other hosts
throughout North America. The mite is active year round in the Christmas tree plantations
of the Willamette Valley in Oregon. The adult is found in or near the one year old bud
scars and the eggs are typically deposited there also.
Life parameters were measured providing a net reproductive rate of 4.23, a mean
generation time of 24.45 days, and an intrinsic rate of increase of 0.059 The intrinsic rate
of increase was low when compared to other predator mites and numerical response to
prey increase would not be possible with such a low rate.
The optimal temperature for the shortest eclosion time (54.4 hr.) and the highest
survival (96.4%) was 26°C. The regression of temperature vs. time to hatch gave a 90%
R² with both the slope and intercept significantly different from zero. Humidities above
70% had survival rates over 96% and eclosion rates in the range of 50-58 hours. The
relative humidity at which 50% of the population died was 58.6%.
The mite was found to feed readily on the pest mite Oligonychus ununguis (spruce
spider mite), as well as Tetranychus urticae (two spotted spider mite), and corn, oak, and
Douglas-fir pollens. The larval form of the predator mite does not require food to molt to
the protonymph, but the protonymph does require food to molt. If water is provided the
entire time from egg to death, the protonymph can survive about ten days. Females
consumed more Tet. urticae than males in both the immature and adult stages. The T.
americanus that were fed corn pollen and Tet. urticae (complete diet) lived for over 115
days. Mites raised on oak and corn pollens did not survive as long (only 70-80 days), and
those raised on Douglas-fir pollens did not reach adulthood. Egg production was observed
on the complete diet, but not on the diets of pollen. The largest number of eggs were laid
around the twelfth day after the molt to adult.
Control and management of field conditions to improve habitat for T. americanus
will be the best approach for its use as a biological control agent. As it does not respond
numerically to prey increase, it will be more effective in a regulatory role to prevent these
increases while the prey is at low levels.