Scanning electron microscopy studies on the first-instar larva of Dermatobia hominis

Abstract. First-instar larvae of Dermatobia hominis collected 1, 4 and 7 days after having penetrated experimentally infected rats, were studied by scanning electron microscope (SEM) observation. On the pseudocephalon there are basiconic and trichoid sensilla (antennal sensory complex), and basiconic, coeloconic and campaniform sensilla (maxillary sensory complex). The thoracic segments bear several rows of small, backwardly pointed, spines, and trichoid, campaniform, coeloconic and pit sensilla. The anterior spiracle is a minute opening. Both small and large spines directed posteriorly are on the first to fourth abdominal segments, which also bear coeloconic and companiform sensilla. These sensilla are present on the unarmed (fifth and sixth) and armed (seventh) abdominal segments. The seventh and the last (eight) abdominal segments have forwardly directed spines. Each spiracular plate has two spiracular openings and four spatulate-like structures called sun rays. The anus and the coeloconic sensilla are proeminent on the last segment. The results are compared with other parasitic dipteran larvae, and emphasize that the multiple types of sensilla on D. hominis larva may have importance in establishing the parasitic phase of the life cycle of this insect.     

Morphology of a newly discovered sensory array on the mouthhooks of Gasterophilus larvae

The distal mouthhooks of Gasterophilus intestinalis (DeGeer) (Diptera: Gasterophilidae) and G. nasalis (Linnaeus) (Diptera: Gasterophilidae) larvae were studied with scanning electron microscopy to determine the morphology of a previously unknown sensory array. The design of the 3rd stage G. intestinalis sensory array was used as the model for comparison to the 2nd stage of this species and the 2nd and 3rd stadia of G. nasalis. Some components forming the sensory array of the 3rd stage G. intestinalis mouthhook were found in 3rd stage G. nasalis. A major difference between these species was the replacement of shallow pits with sensilla-laden troughs in G. nasalis. Second-stage G. intestinalis has a distal mouthhook that varies considerably from the model type, lacking shallow pits and associated peg-like sensilla. By contrast, the sensory array of the 2nd stage G. nasalis larva is the most elaborate yet encountered, with extensive sensilla and troughs. The existence of other types of sensilla on the mouthhook is proposed, as well as a sensory role for the unsculptured surface. Possible uses of the sensory array by the parasite are discussed.     

Scanning electron microscopy of the posterior spiracles of cattle grubs Hypoderma bovis and Hypoderma lineatum

Posterior spiracles of newly hatched first instar larvae of Hypoderma bovis (L.) and H. lineatum (DeVill.) consist of two pairs of spiracular openings. Each pair is surrounded by a rima bearing three spines. Posterior spiracles of second instar larvae are composed of a pair of medial ecdysial scars bounded laterally by spiracular plates. H. bovis spiracular plates have twenty-nine to forty openings, each surrounded by a slightly raised rima. H. lineatum spiracular plates have eighteen to twenty-five openings. Spiracular openings lead to posterior felt chambers which are connected to a common anterior felt chamber filled with a meshlike network. In third instar H. bovis each medial ecdysial scar is surrounded by a strongly concave spiracular plate. Spiracular openings are surrounded by slightly raised rima. Most rimae bear a spine. Spiracular plates of H. lineatum are flat and rimae are without spines. Each spiracular opening leads to a posterior felt chamber, several of which are confluent with a larger anterior felt chamber. Anterior felt chambers open into the dorsal longitudinal tracheal trunk. Felt chambers in third instar larvae are also filled with a complex mesh.     

Comparison of five tests for the serologic diagnosis of myiasis by Gasterophilus spp. larvae (Diptera: Gasterophilidae) in horses and donkeys: a preliminary study

Abstract. Sera from 41 horses and 159 donkeys, from twelve States of México, were tested to ascertain anti-Gasterophilus circulating antibodies by double immunodiffusion (DD), counterimmunoelectrophoresis (CIE), indirect haemagglutination (IH), thin layer immunoassay (TIA) and diffusion-in-gel ELISA (DIG-ELISA) methods using crude somatic antigen from third instar larvae of G.intestinalis (DeGeer). At necropsy, 33/41 horses and 24/159 donkeys were found to be parasitized by G.intestinalis and/or G.nasalis (L.). Gasterophilus intestinalis was the species most commonly found in the equines. Analysis of the sera from the infested animals by DD showed positive results of 21.2% in horses and of 8% in donkeys. Screening the sera with CIE gave sensitivities of 69.7% in horses and of 32% in donkeys. Examination of the sera by IH showed positive results of 87.9% and of 48% in horses and donkeys, respectively. Testing the sera with TIA gave sensitivities of 93.9% in horses and of 96% in donkeys. Analysis of horses' sera by DIG-ELISA showed a sensitivity of 93.9%.     

Ultrastructure of contact-chemoreceptor sensilla found among the genae of female Gasterophilus nasalis

Scanning electron microscopy was used to observe contact-chemoreceptor sensilla in the genae of the anterior vestigial mouthparts of female Gasterophilus nasalis. These were of the uniporous trichoid type and were surrounded by mechanosensory aporous trichoid sensilla of variable size. Contact-chemoreceptor sensilla could be involved in detecting different chemical substances, including the equine kairomones that stimulate females to lay eggs on the hair of the host and/or the short-range sexual pheromones used in precopulatory courtship. The probable functions of these sensilla are discussed with reference to the current literature on the sensorial organs of muscomorphid dipterans.     

A dipteran from south of the Antarctic Circle: Belgica antarctica (Chironomidae) with a description of its larva

Belgica antarctica Jacobs is recorded for the first time from two localities south of the Antarctic circle: Orford Cliff (66°55'S) on the Continental mainland and the Refuge Islands (68°21'S). The larva is described, and measurements of head capsule lengths indicate four instars. The larvae south of the Antarctic circle appear to be slightly smaller than those from within the main distributional range. Belgica antarctica is certainly the earth's southernmost free-living holometabolous insect, but the flea Glaciopsyllus antarcticus has been recorded 14 minutes of latitude farther south than the southernmost records of B. antarctica.     

Light and electron microscopy studies of the midgut and salivary glands of second and third instars of the horse stomach bot,Gasterophilus intestinalis

A morphological study of the midgut and salivary glands of second and third instars of Gasterophilus intestinalis (De Geer) (Diptera: Oestridae) was conducted by light, scanning and transmission electron microscopy. The midgut is anteriorly delimited by a proventriculus, without caeca, and is composed of posterior foregut and anterior midgut tissue from which a double‐layered peritrophic matrix is produced. The midgut can be divided into anterior, median and posterior regions on the basis of the structural and physiological variations of the columnar cells which occur along its length. Two other types of cell were identified: regenerative cells scattered throughout the columnar cells, and, more rarely, endocrine cells of two structural types (closed and open). Different secretion mechanisms (merocrine, apocrine and microapocrine) occur along the midgut epithelium. Abundant microorganisms are observed in the endoperitrophic space of the anterior midgut. The origin and nature of these microorganisms remain unknown. No structural differences are observed between the second and third instar midguts. The salivary glands of G. intestinalis second and third instars consist of a pair of elongated tubular structures connected to efferent ducts which unite to form a single deferent duct linked dorsally to the pharynx. Several intermediate cells, without cuticle, make the junction with the salivary gland epithelium layer. Cytological characteristics of the gland epithelial cells demonstrate high cellular activity and some structural variations are noticed between the two larval stages.     

Sensilla on the antennal funiculus of the horse stomach bot fly, Gasterophilus nigricornis

Gasterophilus nigricornis (Loew) (Diptera: Oestridae) is one of the most damaging obligate parasites of equids in Kalamaili, Xinjiang, China. The main olfactory organs of this stomach bot fly are paired antennae that bear microscopic sensillar structures. The external morphology of the antennal funiculus and sensilla of male G. nigricornis were studied using stereopic microscopy and scanning electron microscopy. A cross-sectional view of the funiculus shows it to be triangular, with an anterodorsal surface, a dorsolateral margin and a posteroventral surface. Almost the entire surface of the funiculus is densely covered with microtrichiae. Small patches lacking these microtrichiae appear as depressions or pits in the surface of the funiculus. Six distinct types of sensilla are recorded, including one trichoid, three basiconic, one auriculate and one clavate sensilla. Trichoid sensilla are the most abundant, followed by the basiconic, auriculate and clavate types in descending order. Only auriculate sensilla are found in pits on the funiculus. Distributions of different sensilla types located on the antennal funiculus are provided. These results are compared with equivalent findings in several other fly species. In addition, the possible functions of the various sensilla types are discussed.     

Modulation of oxygen binding to insect hemoglobins: the structure of hemoglobin from the botfly Gasterophilus intestinalis

Hemoglobins (Hbs) reversibly bind gaseous diatomic ligands (e.g., O2) as the sixth heme axial ligand of the penta-coordinate deoxygenated form. Selected members of the Hb superfamily, however, display a functionally relevant hexa-coordinate heme Fe atom in their deoxygenated state. Endogenous heme hexa-coordination is generally provided in these Hbs by the E7 residue (often His), which thus modulates accessibility to the heme distal pocket and reactivity of the heme toward exogenous ligands. Such a pivotal role of the E7 residue is prominently shown by analysis of the functional and structural properties of insect Hbs. Here, we report the 2.6 A crystal structure of oxygenated Gasterophilus intestinalis Hb1, a Hb known to display a penta-coordinate heme in the deoxygenated form. The structure is analyzed in comparison with those of Drosophila melanogaster Hb, exhibiting a hexa-coordinate heme in its deoxygenated derivative, and of Chironomus thummi thummi HbIII, which displays a penta-coordinate heme in the deoxygenated form. Despite evident structural differences in the heme distal pockets, the distinct molecular mechanisms regulating O2 binding to the three insect Hbs result in similar O(2 affinities (P50 values ranging between 0.12 torr and 0.46 torr).     

Comparative scanning electron microscopy of Gasterophilus third instars

Comparison of cuticular features, including spine distribution and shape, structure of the maxillae and mandibles, the cephalic sensillae and the terminal abdominal segments of third instar Gasterophilus haemorrhoidalis, Gasterophilus inermis, Gasterophilus intestinalis, Gasterophilus meridionalis, Gasterophilus nasalis and Gasterophilus pecorum was conducted using scanning electron microscopy. One or more features distinguished among the species, with the exception of G. haemorrhoidalis and G. intestinalis, which shared all morphological characteristics. The features presented in this study complement and extend those presented in Zumpt's compendium. The function of some features described by Zumpt (e.g. the 'warts' on the rim of the respiratory chamber) is clarified and the presence of previously described sensory structures in the grooves on the maxillae of G. intestinalis is called into question.     

三化螟幼虫的田间分布型

通过采用聚集度指标的方法,对三化螟幼虫在稻田的空间格局进行了系统的研究。测定了幼虫个体群大小、分析聚集原因,为田间抽样、《查定》、及防治提供了依据。     

三点列黄边龙虱幼虫的呼吸系统与生物学特性

对龙虱幼虫的气门结构及体内气管、气囊的构造和分布进行了解剖、描述。通过饲养 ,对龙虱幼虫的栖境、食性、生长发育虫期、残杀性 ,化蛹等行为习性进行了较系统的观察研究。该虫在田间每年2代。     

黄粉虫幼虫对硒的生物积累

在饲料中添加含硒化合物喂养黄粉虫Tenebrio molitor L.幼虫,测定幼虫硒含量、粪便硒含量和体重的变化,计算黄粉虫幼虫特定生长率及幼虫对硒生物积累系数,分析黄粉虫有效积累硒的条件。结果表明,饲料硒含量在15~20mg/kg时,幼虫硒含量明显提高,对硒的生物积累系数高于其它试验组水平,饲料硒含量过高,幼虫硒含量降低,正常生长受到抑制。黄粉虫幼虫特定生长率、取食量、排粪量、干物质含量随着饲料硒含量的增加而降低,死亡率、粪便硒含量随着饲料硒含量的增加而增大。饲料硒含量为15～20mg/kg时黄粉虫幼虫对硒的生物积累效果最好。     

家蝇幼虫活性蛋白组分的提取及清除羟基自由基活性研究

以家蝇MuscadomesticaL.幼虫(蝇咀)为材料,根据溶解度的不同,从脱脂蝇蛆粉中分离出清蛋白、小分子肽、球蛋白、醇溶蛋白、碱溶蛋白等5类蛋白,并测定了它们的含量。结果表明:清蛋白、球蛋白和小分子肽是组成脱脂蝇蛆粉蛋白的主要成分。体外的抗氧化活性实验结果表明:清蛋白和球蛋白都有很好的清除羟基自由基的作用。     

Morphogenesis of the digestive tract of the pluteus larva of Strongylocentrotus purpuratus: sphincter formation

In the developing pluteus larva of S. purpuratus, the initial morphogenetic event in the formation of a functional gut is the appearance of two constrictions in the archenteron. These two constrictions become the cardiac and pyloric sphincters. During the 2 h in which the constrictions form, the sphincter cells change from cuboidal to wedge-shaped, and the apical ends of the sphincter cells develop an electron-dense region in which microfilaments can be resolved. Constriction of the archenteron was reversibly inhibited by cytochalasin B, although cytochalasin B had no effect once the constrictions had fully formed. Neither the electron-dense region nor the microfilaments were observed after cytochalasin B treatment. It is suggested that sphincter formation is initially accomplished by a microfilament-mediated contraction of the apical ends of the sphincter cells, which changes their shape and constricts the archenteron.     

普通齿蛉幼虫的呼吸系统及呼吸行为

研究了普通齿蛉Neoneuromus ignobilis Navás幼虫的呼吸系统及其呼吸行为。结果表明:普通齿蛉幼虫为全气门式(10对气门)呼吸系统,前中胸、中后胸之间、腹部8节各有1对气门,腹部8节各有气管鳃1对,前6对细短,管状,有较短绒毛,后2对气管鳃较粗长,呈羽毛状。腹部1～7节各有1对毛簇,第8腹节无毛簇。侧纵干气管较粗,4束,自前胸前缘部分成左右2组,每组两根侧纵干气管,向胸腹部延伸,二级气管分别伸达各个气门和毛簇,腹部每节由毛簇处的二级气管分支而来的三级气管相连或延伸至消化道等处。气管鳃中无气管。有毛簇呼吸、气门呼吸和体壁呼吸3种呼吸方式,在水中以毛簇呼吸为主,在陆上进行气门呼吸和体壁呼吸。     

冬虫夏草寄主蒲氏钩蝠蛾幼虫的毛序

蒲氏钩蝠蛾Thitarodes pui(Zhang et al.)幼虫是冬虫夏草的寄主昆虫,本文首次对其幼虫毛序进行观察。结果表明,蒲氏钩蝠蛾幼虫头壳刚毛数量、相对位置与多数蝠蛾昆虫一致,但比拉脊钩蝠蛾少了2对刚毛;蒲氏钩蝠蛾幼虫前胸节也比拉脊钩蝠蛾少1对微腹毛;第2、第3胸节毛序相似,均缺失前背毛而多了微背毛、微亚背毛;除第9、第10节外,所有腹节的背毛、侧毛、亚背毛排列是一致的,但是在有足腹节中,亚腹毛为3对,其它腹节亚腹毛仅有2对;除第1和第2腹节具2对微腹毛外,其它腹节微腹毛仅1对,这些微腹毛在排列、长度上均存在一定的差异。     

Cuticular sensilla on newly hatched larvae of Gasterophilus intestinalis and Oestrus ovis

Abstract. Cuticular sensilla on newly hatched larvae of Gasterophilus intestinalis De Geer (Diptera: Gasterophilidae) and Oestrus ovis (L.) were studied by scanning electron microscopy. Two types of trichoid sensilla, two types of coeloconic sensilla and a pit sensillum were present on the thoracic and abdominal segments of G. intestinalis larvae. Sensilla on larvae of O. ovis were similar although only one type of trichoid sensillum was present. Total number of sensilla were higher for O. ovis than for G. intestinalis (248 v . 214). Variation in numbers of sensilla is consistent with the concept that increasing numbers of sensilla are associated with increasingly complex searching behaviour required to locate suitable habitats for development.