Occurrence And Action Threshold Of Major Alfalfa Pests In Ningxia

In this paper, the composition of species of major insect pests, the occurrence regulation of Aphids, Thrips and Loxotage stictalis, and dynamic relationship between major insect pests and their natural enemy were studied. The prevention and control index of Aphids, thrips, Loxotage stictalis and Therioaphis trifolii was made. The results were as follows:1. The insect pests of Alfalfa in Ningxia were abundant. Their distribution was wide, and their occurence rule was complicated. These cause the output of alfalfa to obviously drop and quality to reduce. Investigation shows there are 18 species of main pest of alfalfa. The pests that damage highly the plant are Aphids, thrips and Loxotage stictalis.2. There are 4 species of Aphids that damage alfalfa in Ningxia. Cyrth is mainly distributed in Yellow River Irrigation Area. Aphis craccivora is distributed in countryside. There are 3 species of thrips that damage alfalfa in Ningxia. The advantage population is Odentothrips lati, and it accounts for 90% of the general community. The thrips mainly eats leafbud, tender leaf and flower. The slightly danger cause the top blade to twist, and the seriously danger cause the blade withered for a long time, the blade and flower dry up and fall early. There are 2 species of snout moths that damage alfalfa. The harmfulness of Loxotage stictalis is more setious than Therioaphis trifoll. The former one breaks out in farming and pastoral area in the North of China and have the tendency to aggravate year by year. At present large area of alfalfa offered the effective evidence for the broken-out of Loxotage stictalis.3. Natural enemy resources of insect pests of alfalfa are very abundant. There are 47 species of insect, and including 16 species of natural enemies, 21 species of pests and 10 species of pollination insects. The advantage populations are Adonia variegata, Coccinella septempunctata, Propylaea spp.4. Based on the relationship between Aphis craccivora and losing rate of output, when its EIL in dry field was 9.63%, the control index of Aphis craccivora was 2100 numbers every 100 branches, and its EIL in rice paddy was 6.00%, the control index of Aphis craccivora was 1600 numbers every 100 branches. Based on the relationship between Thrips and losing rateof output, the control index of Thrips was 560 numbers every 100 branches in dry field, and the control index of thrips was 390 numbers every 100 branches in rice paddy. Based on the relationship between Loxotage stictalis and losing rate of output, when its EIL in dry field was 8.90%, the control index of Aphis craccivora was 10 numbers every 100 branches, and its EIL in rice paddy was 6.16%, the control index of Aphis craccivora was 7 numbers every 100 branches. Based on the relationship between Therioaphis trifolii and losing rate of output, when its EIL in dry field was 8.90%, the control index of Aphis craccivora was 45 numbers every 100 branches, and its EIL in rice paddy was 6.16%, the control index of Aphis craccivora was 36 numbers every 100 branches.