干旱区生态环境知识资源中心

Growers of protected crops in semi-arid regions often face a conflict between preventing the entry of small arthropod pests and effective ventilation. This conflict may be alleviated if ventilation openings could be covered only when and where the risk of pests' entry is eminent. In recent years, we determined when and where whiteflies and thrips enter greenhouses and growing tunnels. Open roof vents were major ports of entry for the sweet potato whiteflies. In the fall, when whiteflies' population peaks, over 97% of the whiteflies entered the greenhouses between 7:00 to 13:00 h. The risk of whiteflies entry through the leeward roof vent was twice that of the other vents. This correlated well with a high probability of air inflow at the leeward vents and outflow at the windward vents. The flight of the onion thrips and the western flower thrips was studied using sticky pole traps and similar traps mounted on wind vanes. During most of the year, about 85% of the thrips were caught in the morning and 10% at dusk. Flight time was correlated with periods of low wind speed and thrips were seldom caught when the wind exceeded 10 km/h. Thrips flew mainly upwind during their migration. As most prevailing winds in Israel are from the west, there is a greater risk for thrips invasion from the eastern side of the growing structure. This information may be used to design vents and develop ventilation scheme that will lower the risk of invasion by these pests.