Research On The Occurrence And Control Of The Thrips In Cornfield

The occurrence of the thrips in summer cornfield in summer-sown corn region is caused by the tranformation of the cropping system and the change of the climate in recent years. The corn thrips became the important pest insects in the corn seedling stage. In this paper, experiments were carried out in langfang city, Hebei Province from May to November in 2005, to invetigate the species of thrips and the dorminant species, the spatial pattern, population the occurrence, population dynamics of the thrips and its relationship with the predators, control measures including blue board tempting insects and seeds coated with chemical insecticides, and the suppercooling point of the thrips reared in laboratory was also tested. The results are as follows:1. The species and population dynamics of thrips in cornfield were evaluated by direct observation. Five species thrips were found in cornfield: Anaphothrips obscurus (Miiller) Franklinielle tenuicornis Uzel, Haplothrips aculeatus Fabriecius, Aeolothrips fasciatus (Llinnaeus) and Scolothrips takahashi Priesmer, The main species thrips observed in cornfield are F. tenuicornis (Uzel), A. obscurus (Muller) and H. aculeatus (Febricius). The main species are different as the corn developmentand seasons.2. 1000 corn plants were investigated each time by 5 point sampling method, and number of the thrips on corn plants were recorded. The spatial distribution pattern of thrips in the cornfield is aggregation distribution for the damage behavior of the thrips in cluster.3. The suppercooling point is an important index of resistant to cold. The suppercooling point of Franklinielle tenuicornis Uzel reared in the lab was measured by TMC-40A suppercooling point device. The suppercooling point is a decline curve with one peak.The temperature of thrips gradually decline with time change,but the curve will rise when the temperature reached the suppercooling point, and then decline again when the temperature arrived freezing point. The average suppercooling point of the thrip adult after five months reared in lab is about -10℃, the highest and the lowest is -5. 31 ℃, and — 19. 88℃, respectively, and the freezing point is under the 0℃.4. The main predator species are spiders,ladybird beetles and Onus spp. in cornfield. The number of ladybird beetles and the total number of predators has a very significantly positive relationship with the population of thrips, the population of minutus has a clearly positive relation with the population of thrips, while the population of spiders hasno significant corelation with the population of thrips. It is showed that the ladybird beetles and the Onus spp. are the main predators of thrips in cornfield. The peak time of the predator population is about 20 days later than that of thrips.5.According to the thrips's behavior atttactive to blue colour, the sticky blue boards trap was taken as control measure to control the thrips in corn field. The result showed that the sticky blue boards could reduce the population of thrips, with good control effects, the maximum 75%, lowerest 60%, especially in seedling stage, the control effect could reach 75%.6. The control effects of chemical insectides as seed coating agents were evaluated. Two systemic insecticides, Rengent and Poncho, were selected used for corn seed coating. The control effects of Rengent(300ml, 60%/100kg seed) and Poncho (300ml,50%/100kg seed) could reach 80%, which significantly higher than the two check insecticides, carbosulfan (lOg 20%/100 kg seed) and acetemiprid (1000ml 20%/100kg seed). The two insecticides have no side effects on corn and are safe to predators.