اثر تنش آبی بر تراکم جمعیت برخی آفات اقتصادی محصول یونجه

Considering the climate change and the consequent change in feeding behavior and population growth of pests, it seems necessary to apply solutions in the field of water improvement and the management in farm in order to reduce pest damage. One of the ways to save water is low irrigation. Thus, despite of the importance of the direct moisture factor in the development and growth of pests and its indirect role in the desirability of host plants for pest damage or the level of plant resistance to pests, the evaluating of plant sensitive stages to lack of water is a considerable term in integrated pest management program. For investigations, in a farm that was under subsurface irrigation system for 4 years, four treatments including: 1- Full irrigation (providing 100% of water requirement) 2- Low irrigation with 85% of water requirement 3- Low irrigation with supply 70% of the water requirement and 4- more irrigation to the extent of 115% of the water requirement was done in three repetitions. For investigating the population density of important and economic pests of alfalfa, especially alfalfa leaf weevil, thrips and aphid, sampling was weekly performed in the first and second hays in 1401 and 1402 years. The recorded data related to different densities of the pest population were analyzed using the LSD test in the form of a randomized complete block design. The results of a two-year study on pests in the first two rows of alfalfa showed that irrigation with a level higher than the water requirement of the plant (over-irrigation) will increase the population density and as a result cause damage to some insects, especially leaf-eaters and also alfalfa aphids, and in conditions of low irrigation (Less than the normal requirement of the plant) also increase the population density of sucking insects such as thrips and the important pest of alfalfa spotted aphid. Considering that the effects of herbivorous insects on photosynthesis are through the amount of moisture present in the plant; As a result, the photosynthetic reaction of plants exposed to pest damage and moisture stress can affect the reduction of crop yield.