External Morphology And Inner-ultrastructure Of Compound Eye Of Denroctonus Armandi (coleptera: Phytophaga: Scolytidae)

Chinese white pine beetle, Dendroctonus armandi Tsai et Li (Coleoptera: Scolytidae), isthe main invasive bark beetle in Phytophaga insects, which is native to China. If invaded bythe bark beetles，the Chinese white pine could die quickly and cause serious damage toconiferous wood forest ecosystem. Therefore, this research was designed to study externalmorphology and internal structure of compound eye of Dendroctonus armandi, aiming toprovide a theoretical basis for further exploration of photographic and optical selectionmechanism of D. armandi. The microscopy and electron microscopy techniques were used inthis research, and we came to the following conclusions:(1) The compound eye of the adult D. armandi is long oval and is asymmetricallylocated on the lateral upside of the head and behind the scape of antenna. The morphology ofcompound eyes on the two sides is the same. The surface of the ommatidia is smooth. Thecentral region of the eye are typical hexagonal and account for2/3of the total number offacets. The remaining facets, located closer to the periphery of the eye, are often of irregular,pentagonal, and even squarish shapes. The numbers of ommatidias acreage of the dorsal eyeregion are wider than those of the ventral region. The compound eye of the female and maleof D. armandi consists of244and194ommatidias.(2) Between the separation of ommatidias of adult bark beetles, there are two types ofreceptors: sensilla trichodea (ST) and sensilla chaetica (SCh). The receptors are covered inthe perimeter and rear boundary area of compound eyes. There are2types of hair shapedreceptors outside the female adults’ compound eye: sensilla trichodea I and Ⅱ, while thereare three types of receptors for the male adults: sensilla chaetica, trichome sensilla Ⅱ andsensilla trichodea I. In addition, the interommatidial of the female ommatidias is covered withcorneal nipples.(3) The ommatidium of compound eyes of the D. armandi consists of a cornea, acrystalline cone, two primary pigment cells, eight retinula cells, rhabdom, sixteen secondarypigment cells, basement membrane and axon bundle respectively. The structure of theommatidium of the D. armandi is typical of acone apposition eyes.(4) The male and the female adult of the D. armandi have the same inner-ultrastructure. Two pigment cells (PPC) envelop each group of4cone cells. Their nuclei of the semper cellsare located proximally in middle of the acone. Cross-sections of rhabdoms reveal that theyare developed as ring structures, made up of the rhabdomeres of6peripheral rhabdomeressurrounding2central rhabdomeres. The type of the rhabdom is intermediate between the"open" and "fused" rhabdomeric arrangement of rhabdom. Each retinular cells outside of thecompound eye contains2secondary pigment cells in retina region. We found that arhabdomere corresponds to a retinlar cell from the sagittal plane of the rhabdom. In thevertical sections of ommatidium, the distribution of pigment granules are located throughoutthe entire ommatidium. The configuration rule of the intensity of pigment granules isgradually reduced from crystals to the bottom of the basement membrane.(5) According to the differences of the extro-structure and biological characteristicsbetween the male and female adults of D. armandi, we found that the settling time of thefemale adults is longer than that of the males when they located in the phloem with a verydim light. Although the male and female adults have the same inner-ultrastructure, theresolving power and visibility of the female are better than the compound eyes of the malesof the D. armandi. These differences in the extro-structure characteristics of the compoundeye of the females are better adapted to the dark environment than the male of the adult D.armandi. The type of the partial fused rhabdom corresponds to the behavior habits of the D.armandi, which reflects to the fact that they operate during both day and night.In this research, we carried out a detailed study on the morphological characteristics ofexternal and internal structures of the compound eyes of D. armandi, which showed their theadaptability to the habitat and the coordination between their morphological characteristicsand the behavioural traits of the D. armandi. These also provide the structural theory basis toverify whether compound eye of the D. armandi existence sensory receptors of the two typesin scolytidae. This study has important implications for the D. armandi photosensitivesystems and host selection.