Study On The Predation Of Lygus Pratensis (L.)

Lygus pratensis (L.)was a kind of important pests in cotton fields,but it had been observedto prey on eggs and young larvae of Leptinotarsa decemlineata (Say) in the field. Wheatherthe L.pratensis can prey on other main cotton pests or not,and the predation efficiency ofL.pratensis to pests was not clear. This paper taked the phenomenon of L. pratensis predationas the breakthrough point, systematically researched the functional response of the predatorL.pratensis to Helicoverpa armigera Hübner and A.gossypii Glover, the control function of L.pratensis to H.armigera and the population growth of A.gossypii, and the influences ofdifferent feeding on the growth and development of L. pratensis, in order to clarify thePredation characteristics of L. pratensis,and it gives us a reference to recognite L. pratensis’accurate position in the ecosystem of cotton field. The main results were showed as follows.1.The functional response of L. pratensis to A.gossypii and the eggs and thenewly-hatched larvae of H.armigera were consistented with Holling Ⅱtype.With theincrease of L. pratensis instars, the predation ability of L. pratensis to its prey were graduallyrised,and it could be showed that: female adult> male adult>4thinstar nymphy>2ndinstarnymphy.The2ndinstar nymphy of L. pratensis had few predation ability on the newly-hatchedlarvae of H.armigera, and the4thinstar nymphy was slightly less than male adult on thepredation ability.2.When the initial density of cotton aphid density of10per cage, the population oftreatment was greater than control,however, its population growth rate was extremelyunstable,and lower than controls in General. When the initial density of A.gossypii density of20per cage, L. pratensis lowered population growth of A. gossypii, and the population of theformer was lowered than the later.but there was no significant difference compared with thecontrol group. The growth of the treatment population was lower than controls at the firsttime,then it became higher than controls. There was no significant difference of thepopulation growth rate, between treatment and control,and the trends were like the samewhen the initial density of A.gossypii was40per cage.The predation rate increased basically with the increase of the initial density ofH.armigera eggs.The predation ability of L. pratensis was stronger when the initial density ofeggs was40per cage, the predation rate was26%, and it had little difference compared withthe the predation rate (28.9%)on newly-hatched larvae of H.armigera.3.Only feeding A.gossypii, L.pratensis was dead before finish once molting. The nymphalperiod of the feeding A.gossypii+beans group was less than the grop of only feeding beans.The nymphal survival rate of feeding A.gossypii+beans was significantly less than feedingbeans group.L.pratensis could complete the whole process of growth and development by only feeding H.armigera eggs, and the nymphal period was less than the grop of only feedingbeans. The treatment group of feeding H.armigera eggs+beans was the fastest, each instarperiod was significantly shorter than other treatment groups,and the nymphal survival rate ofL.pratensis feeding H.armigera eggs+beans was significantly higher than other treatmentgroups.The nymphal survival rate of L.pratensis only feeding H.armigera eggs was thelowest.4.There was some slightly differences between the feeding preferences of L.pratensismale and female adult in laboratory.The L.pratensis male adult was preferred to eggs of H.armigera rather than A.gossypii, but the L.pratensis female adult was preferred to A.gossypiirather than eggs of H. armigera.