Predatory Potential Of Amblyseius Herbicolus On Different Prey With Screening Of Alternative Foods

Predatory phytoseiid mites are excellent natural enemies of small arthropod pests such as spider mites,thrips,and whiteflies.Among them,Amblyseius herbicolus Chant is an indigenous dominant predatory mite.It has the advantages of broad feeding habits,wide distribution,strong predation ability,strong ability to break through the wire mesh of spider mites,and certain resistance to chemical agents,which make it a potential biological control agent.In this paper,the predation selectivity,predation function and interference response of A.herbicolus on the dominant species of agricultural pest mite in China,Tetranychus urticae Koch,and the invasive pest western flower thrips,Frankliniella occidentalis Pergande,were investigated in order to clarify its application value in biological control of the two pests.Meanwhile,potential alternative foods for improving its population were screened,and their effects on growth and development,reproduction and cannibalism of A.herbicolus were evaluated.Then the age-stage two-sex life table of A.herbicolus fed continuously on the screened potential alternative foods were constructed so as to further clarify their effects of each selected food on life history and population growth parameters.The results showed that A.herbicolus had a strong predation ability on T.urticae and F.occidentalis,and population of A.herbicolus had an increasing tendency when continuously fed on the selected alternative foods.This study provided technical support for application of A.herbicolus in biological control program.The main results are as follows:1.Predation potential of A.herbicolus on different preyTo determine the control potential of the predatory mite,A.herbicolus,to T.urticae and F.occidentalis,the predations of A.herbicolus on different stages of T.urticae and 1^st and 2^nd instar nymphs of F.occidentalis were examined,respectively.Amblyseius herbicolus showed a predatory preference（Q>1）for larvae and protonymphs of T.urticae,and 1^st instar nymphs of F.occidentalis,which indicated that the predatory mites prefer the juvenile stage of insects and mites.At 19～31℃,all predatory functional response of A.herbicolus on eggs,larvae,protonymphs,deutonymphs and female adults of T.urticae,as well as first and second instar nymphs of F.occidentalis could be modeled as Holling II type.And at 19～28°C,the instant attack rate（a）,predation ability（a/T_h）and daily maximum predation amount（1/T_h）of A.herbicolus on the tested stages of T.urticae and F.occidentalis increased gradually with the increase of temperature,whereas the Handling time（T_h）gradually shortened,and the parameters of predation function response of the predator reached the maximum value at 28℃.Moreover,all the parameters showed a decreasing tendency at 31°C.These results indicate that temperature had a significant effect on the predation ability of A.herbicolus and was the strongest at 28℃.Under the condition of limited predation space and fixed prey densities,the predation amount per predator and predation ration（E）decreased with the increasing of predator density.At 28℃,the interference responses for T.urticae and F.occidentalis were E=0.2113P^-0.5489and E=0.1269P^-0.4334,which indicated that self-interference and competition effect existed in A.herbicolus.2.Screening of alternative foods for A.herbicolusTo screen out alternative foods suitable for the growth,development and reproduction of A.herbicolus,the effects of different alternative foods on its life history and cannibalism were evaluated.The results showed that A.herbicolus could normally complete growth and development and reproduction on all six alternative foods（plant pollens:almond pollen Prunus armeniaca L.,apple pollen Malus pumila Mill,maize pollen Zea mays L.;prey mites:Oulenziella bakeri Hughes,Tyrophagus putrescentiae Schrank,Aleuroglyphus ovatus Troupeau）and natural prey（T.urticae）.The pre-adult development of A.herbicolus,fed on T.urticae,apple pollen and almond pollen,were significantly shorter than that of the other four alternative foods.The mean fecundity of this predator,fed on apple pollen,almond pollen,and O.bakeri,were 28.55,26.06,and 26.02 eggs/female,respectively,which were significantly higher than on the other three alternative foods,while all were lower than the control group,T.urticae（48.95 eggs/female）.Meanwhile,the highest values of intrinsic growth rate（r）of A.herbicolus were obtained on T.urticae(0.210 d^-1)and O.bakeri(0.202d^-1),flowed by almond pollen(0.163 d^-1)and apple pollen(0.155 d^-1),while the lowest was on maize pollen(0.064 d^-1).In addition,cannibalism on conspecific eggs by adults of A.herbicolus did not occur when O.bakeri and T.urticae were provided,but it occurred on the other four alternative foods.Cannibalism rate of the predator was the highest on apple pollen（40%）,the lowest on almond pollen,T.putrescentiae and A.ovatus（10%）.Overall,there were the best comprehensive performance of A.herbicolus feeding on O.bakeri and almond pollen,the results implied that O.bakeri and almond pollen could be the alternative foods,and are suitable for the growth,development,and reproduction of A.herbicolus.3.Life table of A.herbicolus continuously reared on O.bakeri and almond pollenTo assess the effects of single-food continuous rearing on the life history and population parameters of A.herbicolus,the age-stage two-sex life tables of the predatory mite were constructed at its F₂,F₄ and F₆ generations feeding continuously with O.bakeri,almond pollen,and T.urticae（the control group）.The results showed that the pre-adult development of A.herbicolus tended to be prolonged with the increase of rearing generations when reared on O.bakeri and T.urticae,while tended to be shortened on almond pollen.Female adult longevity of A.herbicolus reared on T.urticae and almond pollen were not significantly different between F₂,F₄ and F₆ generations,but female adult longevity of the F₆ generation was significantly shorter than that of the F₂ and F₄generations when reared on O.bakeri.Male adult longevity of this predatory mite was gradually shortened with increasing of rearing generation when fed on T.urticae and O.bakeri,but gradually increased with rearing generation on almond pollen.Pre-adult survival rates of A.herbicolus of the F₂,F₄ and F₆ generations were all 0.96 when reared on almond pollen,which were significantly higher than that reared on O.bakeri（0.86～0.88）,but no significant difference compared with that reared on T.urticae（0.91～0.96）.Meanwhile,among F₂,F₄ and F₆ generations,pre-adult survival rate of A.herbicolus were no significant difference on the same food.The mean fecundity of F₂,F₄and F₆ generations（42.53～48.59 eggs/female）fed on T.urticae were significantly higher than that of alternative foods,O.bakeri（24.37～25.43 eggs/female）and almond pollen（23.71～25.97eggs/female）,while were no significant difference between the generations of A.herbicolus feeding on O.bakeri and almond pollen.Among the population growth parameters,when A.herbicolus fed on almond pollen,there was no significant difference in the net reproductive rate（R₀）between F₂,F₄ and F₆ generations,and the r andλvalues of the F₄ and F₆ generations were significantly higher than that of the F₂ generation,while the average generation period（T）of the F₄ and F₆ generations was significantly shorter than that of the F₂ generation.And when this predator reared on O.bakeri,the R₀,r,λand T values were no significant differences between different generations.In conclusion,when A.herbicolus reared on O.bakeri,the pre-adult development tended to be prolonged with the feeding generations,and female and male adult longevity tended to be shortened,but the mean fecundity of the predator had no significant difference among different generations,and its population parameters were relatively stable in the generations.Meanwhile,the pre-adult development of A.herbicolus reared on almond pollen tended to be shorted with the increase of generations,female adult longevity of the predator had no significant difference among the generations,though male adult longevity had a prolonged tendency,and its population parameters increased with the increase of the generations.Therefore,O.bakeri and almond pollen can be recommended as alternative foods of A.herbicolus for mass rearing programs of this predator or to support its population in the field.In this study,predation ability of A.herbicolus on the agricultural pest T.urticae and the invasive pest F.occidentalis were determined to clarify its predation potential on these two pests.The effects of six alternative foods on the growth,development,reproduction and cannibalism of A.herbicolus were explained,and O.bakeri and almond pollen were screened out as alternative foods for its the population growth.And the effects of single food continuous rearing on the life history and population parameters of predator mite were elucidated,and the feasibility of O.bakeri and almond pollen as A.herbicolus rearing foods were verified.These results provided a theoretical basis for the control of important agricultural pests by A.herbicolus and reference for rearing alternative foods of the predatory mite.