| Host plants are places where herbivorous insects live and feed.In the process of longterm adaptive evolution,there will be certain differences in the growth,development,behavior and morphology of individuals of different host populations of the same species.Sensilla are the structural and functional organ of insects to sense external mechanical stimuli,odor molecules and pheromone,and they affect the physiological activities of insects’ host search,feeding,repelling,courtship and so on.They can not only be used as a distinguishing feature for insect classification,but also provide morphological reference for researching of insects’ evolution and phylogeny.Digestive system and excretory system are important organs for insects to digest food,absorb nutrients,maintain water-salt balance,and excrete.Insects with different feeding habits have different numbers and structures of alimentary canal and Malpighian tubules.Scale insects usually live on branches,leaves or fruits.Studying the types and distribution laws of the antennal sensilla of scale insects on different host plants,analyzing the function of antennal sensilla,and comparing the structures of their alimentary canal and Malpighian tubules can provide theoretical basis for having insights into the sensory system of scale insects and further exploring the adaptability of their host plants.In this study,optical microscope and scanning electron microscope were used to observe the antennal morphology and types,numbers and distribution of the sensilla on the antennae of females and males Spilococcus alhagi and female Eriococcus lagerstroemiae.The mouthparts’ morphology and types,numbers and distribution of the sensilla on the mouthparts of adult females,the morphology and ultrastructure of the alimentary canal and Malpighian tubules of the female adult were also observed.The results showed that there are 6 kinds,11 types sensilla on the antennae of S.alhagi,including 2 types of sensilla trichodea,2 types of sensilla cheatica,2 types of sensilla coeloconica,2 types of sensilla campaniformia,sensilla basiconica and knob sensilla.Sensilla trichodea type I has a slender and smoothe appearance.Sensilla trichodea type II are thicker than type I and have longitudinal grooves.Sensilla chaetica type I and type II are perpendicular to the surface of the antennae.The difference between type I and type II is the length.Sensilla coeloconica are in a socket.The tips of type I are chrysanthemum shape,the tips of type II are blunt.Sensilla campaniformia usually show on the scape and pedicel and the small sensilla campaniformia are intensively show on the distal of the scape.Sensilla basiconica have longitudinal grooves and the tips are blunt.Knob sensilla have a long,not straight rod and a spherical tip.The antennae of female developed conform to the regular pattern of paurometamorphosis and the antennae of male developed conform to the regular pattern of hyperpaurometamorphosis.Sensilla chaetica type II and knob sensilla are unique sensilla of adult males.We found 5 kinds,10 types of sensilla on the antennae of E.lagerstroemiae,including 3 types of sensilla coeloconica,2 types of sensilla campanifomia,2 types of sensilla cheatica,2 types of sensilla basiconica and sensilla trichodea.The distribution of antennal sensilla of 3 instars is similar to each other,which conforms to the general law of antennal development in paurometamorphosis insects.The structure of the mouthparts of the two scale insects composed of labrum,labium,clypeus,crumena,bristles and tentorium,and some of the structures are different in size.The results may be related to their different feeding parts.Both S.alhagi and E.lagerstroemiae have sensilla trichodea and sensilla cheatica,and the numbers are similar.Compared with E.lagerstroemiae,S.alhagi has a different distribution of the sensilla at the tip of the labium,and there is a pair of sensilla coeloconica on the tip of the labium,and sensilla trichodea on labium is densely distributed.The ultrastructural results showed that the structure of the alimentary canal composed of mouthparts,oesophagus,salivary gland,ventriculus,gastric caecum,colo-rectum,rectum and Malpighian tubules,but their surface morphology was not the same,and the length was also quite different.The midguts of the two species of scale insects are not smooth,and the Malpighian tubules has a porous structure.There were no tracheae in the midgut of S.alhagi,and the rectum is smooth.There are some tracheae in the midgut of E.lagerstroemiae,the rectum is extremely uneven,and there are small flaky structures on the rectum surface.In summary,the types and distribution of antennal sensilla,the size of the mouthparts,the size and surface morphology of the alimentary canal and Malpighian tubules of S.alhagi and E.lagerstroemiae are different,indicating the host plant and the location of the feeding parts can affect the morphology of scale insect head’s sensilla,the alimentary canal and Malpighian tubules.This study can provide a theoretical basis for revealing the host adaptive evolution of sensilla of scale insects. |
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