The Impact Of Pollen And Nectar Feeding On Population Fitness Of Hamonia Axyridis And Hippodamia Variegata

The predatory ladybug is an important natural enemy insect in cotton fields,and plays an important role in the control of Aphis gossypii and other pests.In previous studies,it was observed that in addition to preys.Harmonia axyridis and Hippodamia variegata will also feed on cotton pollen,nectar and other plant foods.In this study,we set various feeding treatments and provide ladybugs with prey eggs only,prey eggs+cotton pollen,prey eggs+cotton nectar and other combinations.The parameters,adult longevity,pre-ovipositing periods,total number of spawns,egg hatching rate and others were compared among different treatments to evaluate the effects of cotton pollen,nectar and other foods on the maintenance and promotion of these two ladybird populations.The main research results are as follows:1.In the study on the fitness of adult H.axyridis feeding on different food,the adults fed on Ephestia kuehniella eggs had the longest longevity,up to 148 days in average,with a slow decline in survival rate.The second longest-lived were the adults feeding on E.kuehniella Zeller eggs and cotton pollen mixture and those feeding on cotton pollen lived the shortest period with an average of 9 days and plummeting survival rate.The longevity varied significantly among treatments.In terms of fecundity,the ladybugs feeding on pure cotton pollen were not able to lay eggs.The preoviposition period of ladybugs feeding on E.kuehniella eggs was significantly shorter those feeding on E.kuehniella eggs and cotton pollen.For the former,the total number of single females lays 555 eggs/30 d,and the egg hatching rate is 78%,which is significantly higher than that of the latter.2.The longevity of H.variegata adults feeding on five different kinds of food ranked from long to short,E.kuehniella eggs(63 d),cotton aphids(59 d),cotton nectar(36 d)and cotton pollen(12 d),and the water control(3 d).There was no significant difference between the longevity of ladybugs in treatments feeding on E.kuehniella eggs and cotton aphids.But the differences between other treatments were significant.The female adults did not spawn in treatments feeding on cotton nectar,cotton pollen and water control treatment.The preoviposition period of the treatment fed with cotton aphids was significantly shorter than the treatment fed with E.kuehniella eggs.The former's single female spawning amount reached 646 eggs,and the egg hatching rate reached 80.86%,which was significantly higher than that of the latter.3.The Corcyra cephalonica(Stainton)eggs,Sitotroga cerealella(Oliver)eggs,E.kuehniella eggs,cotton aphids and peach aphids,Myzus persicae(Sulzer)were used to feed H.variegata larvae.The ladybugs all died at the larva period fed with S.cerealella and C.cephalonica eggs.The survival rate of the treatment fed with E.kuehniella eggs was low(23.3%),and only a few developed into adults.The larvae fed with cotton aphids and peach aphids had a stable development,the shortest development period(9 d),a survival rate of more than 88%and more than 80%developing into adults.4.The fitness of different food combinations for adult H.variegata was evaluated by feeding ladybugs with peach aphids and different percentages of cotton pollen.The results showed that the adults fed with peach aphids and cotton pollen in the ratio of 0:1 could not lay eggs with the sharpest decline in the survival rate,and the adult longevity was significantly lower than that in the ratio of 1:0 and 2:1.The adult longevity of the three treatments were 12 d,54 d and 58d respectively.The adult longevity of the treatment in the ratio of 2:1 is significantly longer than that of the ratio 1:0.The preoviposition period(5.8 d)of the treatment in the ratio of 2:1 was significantly longer than that of 1:0 ration treatment.The total number of spawns(842 eggs)of the 2:1 ratio treatment was also significantly higher than that of the latter.But no significant difference in egg hatching rate was found between the two treatments.The thesis clarifies the impact of cotton pollen and nectar on the maintaining and promotion of H.axyridis and H.variegata adult populations.The results shall help to guide the rational application of the corresponding nectar plants in farmland habitats,promote the establishment,maintenance and proliferation of ladybug populations to exert greater pest control function of ladybugs.