Comparative Study Of Internal Organs And External Morphology Of Eucryptorrhynchus Brandti And E.scrobiculatus Larvae

Eucryptorrhynchus brandti and E.scrobiculatus are the borers which only damage Ailanthus altissima.The former larvae feed on the trunks and the latter larvae feed on the roots.The morphology and habit of insects are adapted to their habitat.Therefore the morphological structure of these 2 relative species may be different to adapt to the diverse habitat.In this paper,morphology of external morphology mouthparts digestive tract and respiratory system between E.brandti larvae and E.scrobiculatus larvae were compared.1.There were obvious differences in the morphology of pronotum between E.brandti larva and E.scrobiculatus larva.Except 1st instar larva,larvae of two species can be distinguished rapidly according to the shape and color of the pronotum.The pronotum of larva is dark salmon pink and subquadrate.The area of punctum is wide and intersection angles of both sides of trailing edge are acute angles.The pronotum of E.scrobiculatus larva is light orange and oblate.The area of punctum is narrow and intersection angles of both sides of trailing edge are obtuse angles.The pronotum of the 1st instar larvae of two species weevil are very small,and the details are difficult to observe with the lightly color.Therefore they can not be distinguished according to the shape of the pronotum,but they can be distinguished according to the foraging behavior.After hatching the 1st instar E.scrobiculatus larva explores widely and it is very good at crawling.Once the proper position is found,it perpendicularly climbs into the feed.The 1st instar E.brandti larva is not good at crawling and moves slowly.It often stops moving in somewhere,supports itself with tail,stands upright and stretches body upward.2.The mouthparts of E.brandti larva and E.scrobiculatus larva are composed by epopharynx,mandible,pregenae and labium.The tongue is degenerate.Compared to E.brandti larva,the mandibles of E.scrobiculatus larva is narrower,the cutting teeth is more bent inward,and the cutting teeth and molars are more blunt.It can be inferred that the ability of cutting down the food of E.scrobiculatus larva is weaker than that of E.brandti larva.3.The digestive tract of larva and E.scrobculatus larva are divided into foregut,midgut and hindgut.The foregut is short,while the midgut is long.The midgut is divided into two parts.The anterior part is intumescent and has several herringbone folds.The posterior part is a smooth tube.A dense arrangement of finger-shaped gastric cecum was found on both sides of the middle and posterior part of midgut.The hindgut is composed of ileum and rectum.6 Malpighian tubules can be found in the digestive tract.The structure of digestive tract of E.brandti larvae and E.scrobiculatus larvae of different instar were similar,but only slightly different in the morphology.The end of foregut of 6th and 7th instar larvae of E.brandti were slightly dilated as narrow and long kettle shapes,which were suspected to be a crop.The end of foregut of 5th and 6th instar larvae of have obvious near-globular dilation.It indicated that E.scrobiculatus larvae need to storage food more than E.brandti larvae do.The growth rate and the proportion of the midgut were both higher than those of foregut and hindgut in two species larvae.Indicating that the larvae focused on the digestion and absorption capacity of the digestive tract.4.E.brandti larva has nine spiracles placed on mesothorax and 1st to 8th abdomal segments.The type of spiracle is internat closing apparatus.They are long ellipsoid or ovate with longitudinally cracked and sunken.Per-itreme is orange and ossific.Trachea distributed on both sides of body and spiracular trachea is divided into 4 branches.Lung-like structures were not found.5.Morphological structure of E.brandti larva and E.scrobiculatus larva are different for adapting diverse habitat.For example,1st instar E.scrobiculatus larva has long setae and full-grown somite for drilling into the soil layer to find root.1st instar E.brandti larva have longer setae on both sides of the head and tail for searching and sustaining when feeding.The end of foregut of 5th and 6th instar E.scrobiculatus larvae have obvious near-globular dilation to storage food for adapting to the process of searching in the soil.E.brandti larvae don’t need to storage food and the end of foregut have no or slight dilation.