水稻种植密度和生育期对三化螟卵天敌种群及其效益的影响

研究结果表明，水稻种植密度和生育期对三化螟Scirpophaha incertulas卵的天敌种群及其捕食串和寄生率有显著的影响。捕食性天敌和某些寄生蜂的种群密度随种植密度的增加和生育期的增长而增加，但啮小蜂和赤眼蜂对种植密度的反应不明显。螟卵捕食串随种植密度的增加和生育期的增长而增加。但螟卵寄生率则相反：种植密度低、生育期早，卵寄生率高，且差异显著。种植密度和生育期不仅影响了单种寄生蜂的寄生率，而且也影响了螟卵寄生蜂种类的多少。在种植密度低的地块和水稻生长初期，卵块通常有3种寄生蜂出现，而在密度高的地块和生长末期，卵块通常没有寄生蜂或仅有赤眼蜂出现。虽然卵捕食和卵寄生都是三化螟卵的重要控制因素，但由天敌所造成的卵死亡率则随种植密度的增加或生育期的延长而下降。

PREDATION AND PARASITISM OF YELLOW STEMBORERSCIRPOPHAGA INCERTULAS (WALKER )EGGSINFLUENCED BY RICE PLANT DENSITYAND GROWTH STAGES

he incidence of predation and parasitism on egg masses of the yellow stemborer Scirpophaga incertulas (Walker) and related natural enemy populations weremonitored under four rice planting densities (900000, 660000, 550000, and 160000hills/ha) and growth stages (20,40,60 and 80 days after transplanting [DAT]) fortwo seasons. Egg predation was significantly higher at 20 and 40 DAT but not atthe later stages although the predator populations increased as the planting densityincreased and season progressed. Conversely, egg parasitism declined as the plantingdensity increased and season progressed. At the higher planting density and later in theseason parasitism declined along with number of species per egg mass. In general.egg mortality caused by predators and parasites declined significantly as the plantingdensity increased and the season progressed even though the enemy population increased. The significance of conservation and utilization of natural enemies of rice pestsby manipulation of the planting density is discussed.