Studies of the biology and effectiveness of Laricobius erichsonii Rosenh. (Coleoptera: Derodontidae), an European predator of the balsam woolly aphid, Adelges piceae (Ratz.) (Homoptera: Adelgidae)

Graduation date: 1960The balsam woolly aphid (Adelges piceae (Ratz)), an\ud European pest of conifers, was first discovered in the\ud Pacific Northwest shortly after 1930. Control measures\ud of a chemical, silvicultural, or biological nature have\ud been proposed. However, present control methods are either\ud too costly or do not result in satisfactory control of the\ud aphid.\ud Several insect species were reported as predaceous\ud upon the balsam woolly aphid in Europe, eastern Canada,\ud and the Pacific Northwest. European predators of this\ud pest have been imported into eastern Canada in an effort\ud to find a satisfactory control measure. Several species\ud of insects from Europe were imported into the Pacific\ud Northwest from 1957 through 1959. Laricobius erichsonii\ud was successful in becoming at least temporarily established\ud in this region and was chosen for further study.\ud The purpose of the thesis project was to obtain information\ud on the establishment, life history, habits, and\ud effectiveness of this beetle in Oregon and Washington.\ud Studies were begun in May of 1958 and terminated in\ud November of 1959.\ud Two species of the genus Laricobius are indigenous\ud to the Pacific Northwest. Franz has studied the life\ud history and ecology of L. erichsonii in Europe, and Clark\ud and Brown have made observations of establishment, spread,\ud life history, habits, and effectiveness in eastern Canada.\ud In 1958 and 1959, 10,125 L. erichsonii, adults were\ud collected in Czechoslovakia and sent to the Pacific\ud Northwest Forest and Range Experiment Station in Portland,\ud Oregon, for release in the Pacific Northwest. Predators\ud were released either freely or in cages at eight different\ud areas in Oregon and Washington. Temporary establishment\ud occurred at all of the release areas regardless of\ud varied weather and elevational differences.\ud Some 52 larvae were collected and mounted on slides\ud in 1959. Of these larvae, no first, one second, four\ud third, and 47 fourth instars were present. First and\ud second instar larvae tend to stay within the aphid's wax\ud masses, while third and fourth instar larvae wander about\ud the bark in search of food. Moulting was observed. At\ud the various release areas, larvae were recovered from\ud May 23 through August 26 of 1959 and adults from May 5\ud through September 2.\ud Two pupae were laboratory-reared from five, field-collected\ud fourth instar larvae. Under laboratory conditions,\ud one fourth instar larva consumed or destroyed seven\ud eggs and two adults in a period of one and one-half hours.\ud L. erichsonii adults prefer aphid adults but attack other\ud stages.\ud Range of observed dispersal, a year following release,\ud ranged from zero to 75 feet from the point of original\ud release.\ud A study was initiated at Benton-Lane, Oregon, to\ud study the effectiveness of L. erichsonii in reducing\ud balsam woolly aphid populations. Trend of host populations\ud was evaluated at approximately two week intervals\ud on six unprotected and two protected (control) one-inch-square\ud bark plots on a pole-sized grand fir surrounded by\ud a six-foot-cube study cage. On the protected plots, the\ud average aphid population increased from 31 to 131 individuals\ud in the period from May 1 through November 23 of 1959,\ud while on the unprotected plots it increased from 47 to 64\ud individuals.\ud A t-test was calculated to see if the differences\ud between protected and unprotected plot populations were\ud significant. The t-value obtained was 4.3, which showed\ud that the differences were significant at the one per cent\ud significance level.\ud It is felt that populations of the balsam woolly\ud aphid will be greatly reduced when L. erichsonii can combine\ud with other predators that are fairly host specific\ud and that prey on all stages of the aphid