Chemical control of Apriona germari (Hope) larvae with zinc phosphide sticks

Larvae of Apriona germari (Hope), found widely in China, cause serious damage to trees and are difficult to control. Since some biological control methods have not been applied effectively in the field, chemical control methods are used widely. Because of low cost, no poisonous residues and relatively safe application, zinc phosphide sticks have been tested to control the larvae as a matter of urgency. However, there were no criteria about the dosage and use. Given the characteristics of larvae tunnels on triploid Populus tomentosa trees and the one-on-one way of using poison-fumigated sticks, the larvae were treated by three treatments with zinc phosphide sticks. The treatments are as follows:inserting one stick into the first hole of the tunnel from bottom to top (T1), inserting a stick into each of the lowest two holes (T2) and inserting one stick into the first and third hole from bottom to top separately (T3). We cleared the frass around the holes and on the ground before inserting the sticks and blocking every hole with mud for each treatment. After the fourth investigation was carried out, the larvae of CK were still active, and had caused serious damage and emanated fresh frass from old and new holes. Some larvae treated with T1 and T2 were in an intermediate state, but all of the larvae treated with T3 died completely and their old holes had healed. The results show that inserting zinc phosphide sticks (the extent of dispersion of the sticks was 20%) is a feasible method to control A. germari (Hope) larvae in triploid P. tomentosa of pulpwood trees. Because there were no statistically significant differences (p>0.05) among the three treatments, we recommend that T1 should be used for economic efficacy.