| Life style of Phytoseiidae(Acari:Mesostigmata)species is an important feature in evaluating their potentials in as biological control agents.However,limited practical methods have been provided to estimate life style of phytoseiid mites without detailed biological experiments or wide range of rearing attempts,which means it will be very difficult to evaluate the biological control potential of species newly discovered or have not been well be studied.Previous studies suggested that some morphometrics of gnathosoma and the intrinsic rate of increase(r_m)be related to the feeding habits of phytoseiids.Therefore we want to ensure whether there are common features in terms of both gnathosoma structure and r_m of the species within the same life type group that can be achieved easier than trying to rear them on all possible prey?However,the mouthpart or gnathosoma structure has not been described comprehensively.So,our studies were conducted from three following aspects:In first section,we observed fine mouthpart structures of Phytoseiulus persimilis under scanning electron microscope(SEM)and cross sections of P.persimilis esophagus under transmission electron microscope(TEM).We summarized the mouthpart of Phytoseiulus persimilis as comprised of chelicerae,pedipalpi,salivary styli,mouth(tongue,labrum,supralabrum),and hypostome(corniculi and internal malae).Two mouthpart fine structures,salivary styli groove and ostiole on the tip of fixed digit,were first described.Besides,we revised the terminologies of labrum and paralabrum.The esophagus of this species is not uniform.Instead,it comprises a semi-enclosed preoral cavity,an oral cavity and a pharyngeal chamber with Y-shaped cross section.We also improved the descriptions of its feeding process through observing specimens in the state of feeding under SEM.During each hunting process,P.persimilis protracted their chelicerae,had movable digits piercing into the prey and grabbed it.As the chelicerae retracted,the tips of its corniculi and embedded salivary styli also pierced into the prey.Based on our observation,P.persimilis does not have a pair of styli as piercing-sucking arthropods do.Its piercing and sucking functions were implemented with chelicerae and hypostome,respectively.Therefore,we define its mouthpart type as pseudo-piercing-sucking mouthpart.In second section,scanning electron microscope pictures of 10 Phytoseiid species belonging to four major life styles(I-specialized predators of tetranychus species,Ⅱ-selective predators of tetranychid mites,Ⅲ-generalist predators,Ⅳ-specialized pollen feeders(McMurtry and Croft,1997))were taken.For each species,24 morphometrics of gnathosoma including the length of dorsal shield were measured.Principle Component Analysis(PCA)showed that the 10 species can be divided into three groups based on the first two principle components of these parameters.The 1st group includes Phytoseiulus persimilis(Athias-Henriot)and Neoseiulus californicus(McGregor),Neoseiulus womersleyi(Schicha),the 2nd group includes six predators Amblyseius orientalis(Ehara),Amblyseius swirskii(Athias-Henriot),Amblyseius tsugawai(Ehara),Neoseiulus barkeri(Hughes),Neoseiulus bicaudus(Wainstein),Neoseiulus cucumeris(Oudemans),and the 3rd group includes Euseius utilis(Liang&Ke).This grouping is consistent with the life style division of McMurtry&Croft.In last section,to investigate whether r_m varies among four basic life styles(feeding habits)of predatory mites,we summarized 265 r_ms of 48 species within 13 genera from 249 references that studied development and reproduction of phytoseiid mites since 1970.Selected data matched 2criterions 1)experiments were conducted at a constant temperature between 23°-27°C;2)sufficient natural prey were provided.r_m for phytoseiid mites using Tetranychus spp as prey of type I(0.288±0.005)and type Ⅱ(0.266±0.003)were higher than those of type Ⅲ(0.176±0.007)and type Ⅳ(0.168±0.006).Overall,we could primarily divide Phytoseiidae species into different life styles based on their gnathosoma structure parameters and r_m when feeding on Tetranychus spp.And we could divide Type Ⅱ and Ⅲ,which has always been a difficulty in previous studies. |
