THE INVESTIGATION ON THE LARCH APHIDS IN BOTANICAL GARDEN OF HEILONGJIANG PROVINCE
Fang San-yang Zhong He (Northeast Forestry College) Ling Yong-mu (Botanical Garden of Heilongjiang Province)
Among the main trees for making cities green is larch which is appreciated for its rapid growth, pretty shape and easy plantation. But larch is often attacked by some insects. During 1982—1983, we made investigations on the pest insects in the larch forest of the provincial botanical garden situated in the suburb of Harbin and we also designated standard trees which are observed regularly.Four species of aphid, which were found on the standard trees of 25 years old Dahurian Larch (Larix daharica), caused serious damage. They are as follows: Adelges laricis Vall., Sacchiphantes viridis Ratz., Cholodkovskya viridana Chol. and Cinara laricis Walker.Even though the above-mentioned 4 species live together、the appearing time is dependent on the individual species and the damaged places on trees are also different. This can alleviate the competition among them and would be conducive to the development and reproduction of them.We think that under the conditions of the city, the major reasons for aphids to appear numerously are that the light in the forest has been improved and both the variety and the number of natural enemies have become less except the aphids' strong reproduction ability, suitability and the ants' taking care of them.It was found during the investigation that there is a interrelation between the thickness of bark and the number of A. laricis and S. viridis; the abhids prefer living under the thin bark; so the trees with thin bark are more vulnerable than the ones with thick bark.A. laricis and S. viridis choose Koyama Spruce (Picea koroiensis) as the second host; so the larch near Koyama Spruce is more susceptible to being harmed. It should be noted in affcrestation that larch and Spruce should be separated.The principles to control these pests in cities should be:prevention, import and protection of natural enemies, quarantine imposed to the imported larch and spruce seedlings. If pest damage occurs, pesticide should be used as less as possible. Furadan-insecticide is suggested to be applied against aphid, but the applying time and dose must be correct.The density and light should be considered at the beginning of forestation. The artificial wood should have proper density.