Molecular Characterization of Gregarines from Sand Flies (Diptera: Psychodidae) and Description of Psychodiella n. g. (Apicomplexa: Gregarinida)

ABSTRACT. Sand fly and mosquito gregarines have been lumped for a long time in the single genus Ascogregarina and on the basis of their morphological characters and the lack of merogony been placed into the eugregarine family Lecudinidae. Phylogenetic analyses performed in this study clearly demonstrated paraphyly of the current genus Ascogregarina and revealed disparate phylogenetic positions of gregarines parasitizing mosquitoes and gregarines retrieved from sand flies. Therefore, we reclassified the genus Ascogregarina and created a new genus Psychodiella to accommodate gregarines from sand flies. The genus Psychodiella is distinguished from all other related gregarine genera by the characteristic localization of oocysts in accessory glands of female hosts, distinctive nucleotide sequences of the small subunit rDNA, and host specificity to flies belonging to the subfamily Phlebotominae. The genus comprises three described species: the type species for the new genus— Psychodiella chagasi ( Adler and Mayrink 1961 ) n. comb., Psychodiella mackiei ( Shortt and Swaminath 1927 ) n. comb., and Psychodiella saraviae ( Ostrovska, Warburg, and Montoya-Lerma 1990 ) n. comb. Its creation is additionally supported by sequencing data from other gregarine species originating from the sand fly Phlebotomus sergenti . In the evolutionary context, both genera of gregarines from mosquitoes ( Ascogregarina ) and sand flies ( Psychodiella ) have a close relationship to neogregarines; the genera represent clades distinct from the other previously sequenced gregarines.     

The life cycle and host specificity of Psychodiella sergenti n. sp. and Ps. tobbi n. sp. (Protozoa: Apicomplexa) in sand flies Phlebotomus sergenti and Ph. tobbi (Diptera: Psychodidae)

Two new gregarines in the recently erected genus Psychodiella (formerly Ascogregarina), Psychodiella sergenti n. sp. and Psychodiella tobbi n. sp., are described based on morphology and life cycle observations conducted on larvae and adults of their natural hosts, the sand flies Phlebotomus sergenti and Phlebotomus tobbi, respectively. The phylogenetic analyses inferred from small subunit ribosomal DNA (SSU rDNA) sequences indicate the monophyly of newly described species with Psychodiella chagasi. Ps. sergenti n. sp. and Ps. tobbi n. sp. significantly differ from each other in the life cycle and in the size of life stages. The sexual development of Ps. sergenti n. sp. (syzygy, formation of gametocysts and oocysts) takes place exclusively in blood-fed Ph. sergenti females, while the sexual development of Ps. tobbi n. sp. takes place also in males and unfed females of Ph. tobbi. The susceptibility of Phlebotomus perniciosus, Phlebotomus papatasi, Ph. sergenti, Ph. tobbi, and Phlebotomus arabicus to both gregarines was examined by exposing 1st instar larvae to parasite oocysts. High host specificity was observed, as both gregarines were able to fully develop and complete regularly the life cycle only in their natural hosts. Both gregarines are considered as serious pathogens in laboratory-reared colonies of Old World sand flies.     

Host-parasite relationships of Ascogregarina chagasi (Eugregarinorida, Aseptatorina, Lecudinidae) in Lutzomyia longipalpis (Diptera: Psychodidae)

The life cycle of Ascogregarina chagasi in larvae and in adult female Lutzomyia longipalpis was studied by light and electron microscopy. Sporozoites and young gamonts were attached to the epithelial lining of the larval midgut via an osmiophilic contact zone. The mucron of young gamonts was bordered by an invaginated pellicular fold, and an electron-opaque vesicular structure was observed adjacent to it. Sporozoites possessed an apical complex and were bound by a double membrane with underlying subpellicular microtubules. The gamont pellicle was uniformly corrugated and consisted of two cortical membranes and a plasma membrane. Mature gamonts and gametocysts were found in the posterior ectoperitrophic space of third and fourth instar larval midguts and in the haemocoel of adult flies. Gametocysts in adult females adhered to the genital accessory glands, where they were encased in electron-dense capsules secreted by the fly through haemocyte-mediated humoral immune reactions. Oocytes were spindle-shaped and bound by a double-layered wall with a discernible polar plug at each end. Sporulation was endogenous, occurring within gametocysts in the midguts of larvae or the accessory glands of adult females. FITC-phalloidine staining of all stages of A. chagasi except mature gametocysts produced bright fluorescence, indicating the presence of a diffuse, actin-like protein in the cytoplasm.     

Breeding sites of Phlebotomus sergenti, the sand fly vector of cutaneous leishmaniasis in the Judean Desert

Phlebotomine sand flies transmit Leishmania, phlebo-viruses and Bartonella to humans. A prominent gap in our knowledge of sand fly biology remains the ecology of their immature stages. Sand flies, unlike mosquitoes do not breed in water and only small numbers of larvae have been recovered from diverse habitats that provide stable temperatures, high humidity and decaying organic matter. We describe studies designed to identify and characterize sand fly breeding habitats in a Judean Desert focus of cutaneous leishmaniasis. To detect breeding habitats we constructed emergence traps comprising sand fly-proof netting covering defined areas or cave openings. Large size horizontal sticky traps within the confined spaces were used to trap the sand flies. Newly eclosed male sand flies were identified based on their un-rotated genitalia. Cumulative results show that Phlebotomus sergenti the vector of Leishmania tropica rests and breeds inside caves that are also home to rock hyraxes (the reservoir hosts of L. tropica) and several rodent species. Emerging sand flies were also trapped outside covered caves, probably arriving from other caves or from smaller, concealed cracks in the rocky ledges close by. Man-made support walls constructed with large boulders were also identified as breeding habitats for Ph. sergenti albeit less important than caves. Soil samples obtained from caves and burrows were rich in organic matter and salt content. In this study we developed and put into practice a generalized experimental scheme for identifying sand fly breeding habitats and for assessing the quantities of flies that emerge from them. An improved understanding of sand fly larval ecology should facilitate the implementation of effective control strategies of sand fly vectors of Leishmania.     

About the presence of Phlebotomus sergenti Parrot, 1917 (Diptera: Psychodidae) in Eastern Sicily, Italy

The note reports the data of a three-year sand fly investigation (1997-99) carried out in Eastern Sicily (Italy) with the aim to study the distribution of Phlebotomus sergenti. The survey involved a densely inhabited area at the foot of Mount Etna and the area of Iblei mounts. A total of 9,095 sand flies, of which 63.4% males, were captured. Five species belonging to the genus Phlebotomus (P. perniciosus, P. perfiliewi, P. neglectus, P. sergenti and P. papatasi) and one to the genus Sergentomyia (S. minuta) were identified. Both the prevalence and distribution of the species were different within the two areas studied. In Mount Etna area, P. perniciosus (77.7%) was the prevalent species followed by S. minuta (19.8%), P. sergenti (2.0%), P. neglectus (0.3%) and P. papatasi (0.2%). While in Iblei mounts region S. minuta (84.5%) showed the highest prevalence, followed by P. perniciosus (14.4%), P. perfiliewi (0.9%) and P. neglectus (0.1%). Here, P. sergenti was a very rare species (< 0.02). P. sergenti was mostly associated to domestic habitats of peri-urban and urban zones located between two and 750 m a.s.l. The density values of P. sergenti, expressed as number of specimens/m2 of sticky trap, were between 0.3 and 5.5 with the highest value in the hilly collecting sites. The low observed abundance of P. sergenti does not allow to draw any prediction on the role that the species could play in the transmission of leishmaniasis in Sicily.     

Midgut pH profile and protein digestion in the larvae of Lutzomyia longipalpis (Diptera: Psychodidae)

The sand fly Lutzomyia longipalpis is the vector of Leishmania infantum, the etiological agent of American visceral leishmaniasis. Despite its importance, until now the internal anatomy of the immature forms has never been described and little is known about their digestive processes. In nature, sand fly larvae feed on organic detritus in the soil, constantly ingesting large amounts of material. The objective of this study was to describe the anatomy of the gut and the pH of the gut lumen, as well as to investigate the proteases responsible for protein digestion. The larvae have a short gut with a prominent, well-developed midgut. Ingestion of food containing indicator dyes permitted the gut pH to be measured. A pH gradient was observed, varying from >9 in the anterior midgut to 6.5-7.0, in the posterior midgut. The endoproteolytic enzymes are secreted in the anterior midgut and are able to digest azocasein over a large pH range, specially at pH 11. Studies with various inhibitors indicated that the digestive endoproteases are trypsin- and chymotrypsin-like enzymes. These results were confirmed by using the substrates BApNA and N-CBZ-L-PpNA, specific for trypsin and chymotrypsin, respectively. Aminopeptidases were also investigated with p-nitroaniline-derived substrates. These enzymes are located in the posterior midgut, bound to the membranes and functioning at an optimal pH of 6.5-8.0. The results presented here are consistent with the current proposal that proteins are digested to peptides in the anterior midgut inside the endoperitrophic space and subsequently undergo digestion in the ectoperitrophic space of the posterior midgut.     

Posterior spiracles of fourth instar larvae of four species of phlebotomine sand flies (Diptera: Psychodidae) under scanning electron microscopy

In the present study, posterior spiracles of laboratory-reared fourth instar larvae of Lutzomyia longipalpis, L. migonei, L. lenti, and L. whitmani (Diptera: Psychodidae) of the State of Ceará, Brazil, were examined under scanning electron microscopy. The number of papillae of spiracles examined varied according to the species examined, but no intraspecific differences were found. The importance of this structure to sand fly larva identification and phylogeny is commented.     

Effect of wheat germ agglutinin on formation and structure of the peritrophic membrane in European corn borer (Ostrinia nubilalis) larvae

European corn borer (ECB; Ostrinia nubilalis (Hubner)) larvae (third instar) fed 0.05% w/w wheat germ agglutinin (WGA) in their diet for 72 h showed very little increase in body weight, whereas weight of control larvae increased nearly fourfold. Light and transmission electron microscopy studies showed that the morphology of the peritrophic membrane (PM) changed within 24 h after ECB larvae fed on the WGA diet. Whereas the PM in the anterior region of the midgut was a thin membranous structure in control larvae, the WGA-fed larvae secreted a multiple-layered and unorganized PM that contained embedded food particles, bacteria, and pieces of disintegrated microvilli. Gold-labeled WGA was localized specifically in the PM and microvilli. The PM of WGA-fed larvae was inundated with dark-staining amorphous structures that, when incubated with anti-WGA, showed heavy WGA localization. The antibody label indicated that most of the ingested WGA was found in the PM, with lesser amounts on the microvillar surface and the least amount within the epithelium. After 72 h, the middle portion of the mesenteron revealed a thin, compact PM in the control larvae, whereas the PM of the WGA-fed larvae was multilayered and discontinuous, which allowed plant cell-wall fragments to penetrate into the microvilli of the epithelium. Scanning electron microscopy of PMs from fifth instar ECB larvae fed the WGA diet revealed a breakdown in the chitinous meshwork by 48 h after initiation of feeding. The endo-PM surface from control larvae was smooth and intact, whereas the PM of WGA-fed larvae showed disintegration of the meshwork and a reduced proteinaceous matrix. This allowed bacteria and food particles to penetrate through the PM into the ectoperitrophic space and directly contact the microvilli. Therefore, WGA, a protein inhibitor of larval growth, interferes with the formation and integrity of the PM, which exposes the brush border to ingested material. This, in turn, appears to stimulate secretion of additional PM layers, the concomitant disintegration of the microvilli, and cessation of feeding.     

A comparison of the intraspecific variability of Phlebotomus sergenti Parrot, 1917 (Diptera: Psychodidae).

Phlebotomus sergenti populations from different areas of the Mediterranean basin are known to exhibit high intraspecific variability. Previous studies of ITS2 revealed the presence of two branches that may represent sibling species. To corroborate this finding by other tools, two colonies of P. sergenti originating from Turkey and Israel, each belonging to a different ITS2 branch, were compared by three different methods: geometric morphometric analysis of wing shape, RAPD (random amplified polymorphic DNA), and cross-mating study. For geometric morphometric analysis, two-dimensional Cartesian coordinates of 16 landmarks from the wings were digitized and analyzed. Significant shape differences were found between colonies but not between sexes within each colony. RAPD results formed two distinctive clades corresponding to the origin of the colony but also showed heterogenity among members of both colonies. In cross-mating studies, viable hybrid F1 and F2 progeny were obtained when both Turkish males/Israeli females and Israeli males/Turkish females were crossed. F1 progeny was included in RAPD analysis and these hybrids formed a distinctive clade with an intermediate position between the two parental clades. No significant differences were found in egg production of crossed sand flies. The cross-mating study showed that there is no reproductive barrier between P. sergenti from different geographical areas. On the other hand, RAPD and geometric morphometric analysis revealed a significant difference between colonies and confirmed the suitability of previous ITS2 analysis for discrimination among sand fly populations. Further development of molecular markers should resolve a possible existence of sibling species within Phlebotomus sergenti.     

Bacteria Associated with the Ectoperitrophic Space in the Midgut of the Larva of the Midge Xylotopus par (Diptera: Chironomidae)

An ectoperitrophic association of bacteria with the midgut of Xylotopus par larvae was investigated by scanning electron microscopy and transmission electron microscopy. The bacteria attached to the epithelium as a well-defined band in the posterior midgut. They were morphotypically uniform and formed short filaments with endosporelike structures. The consistent presence and well-defined location of the bacteria in a region of the insect digestive tract usually void of microbes indicates a highly evolved symbiotic association, the nature of which is unknown at present.     

Cytology of Leidyana canadensis (apicomplexa: eugregarinida) in Lambdina fiscellaria fiscellaria larvae (lepidoptera: geometridae)

The eugregarine Leidyana canadensis infects the larval gut of the eastern hemlock looper, Lambdina fiscellaria fiscellaria. Guts of infected larvae were chemically fixed, embedded in epoxy resin, and sectioned for light and electron microscopy to describe the cytology of L. canadensis and its pathology in the larval host. Oocysts of L. canadensis are ingested by larval hemlock looper. Trophozoites emerge from the oocysts, pass through the peritrophic membrane into the ectoperitrophic space, and attach to the epithelium of the midgut by means of an apical epimerite. The epimerite does not actually penetrate the affected epithelial cell; instead, it causes an invagination of the plasma membrane of the cell. The center of the epimerite contains membrane cisternae, and mitochondria line its periphery. Microtubules and mitochondria in the host cell cytoplasm surround the epimerite. At the light microscopic level, there appeared to be septa between the epimerite and the protomerite and between the protomerite and the deutomerite; however, in the electron microscope, no septa were evident. Only differences in the concentrations and nature of the inclusions in the cytoplasms of these three regions were apparent. The deutomerite contains a single nucleus in the central-posterior area. After an undetermined period, the epimerite detaches from the host gut epithelium and is withdrawn into the protomerite, and the trophozoites float freely in the ectoperitrophic space before differentiating into gamonts. Division of the single, large nucleus into numerous small nuclei appears to occur prior to syzygy. Gamonts pair and a cyst wall is laid down around them, forming a gametocyst. Oocysts are extruded from mature gametocysts, in chains, through sporoducts.     

桔小实蝇、木瓜实蝇和番石榴实蝇耐热性的热动力学分析

果实蝇属是重要的检疫性有害生物之一, 其中桔小实蝇Bactrocera dorsalis (Hendel)、 木瓜实蝇B. papayae Drew & Hancock和番石榴实蝇B. correcta (Bezzi)近几年在口岸检出率居高。本研究利用热水浸泡处理法比较这3种实蝇的卵、 1龄幼虫和3龄幼虫在44~47℃下的耐热性, 利用热动力学模型和活化能比较每种实蝇的耐热虫态以确定耐热种。结果表明： 在测定温度范围内, 3种实蝇卵、 1龄幼虫和3龄幼虫的死亡率都与处理时间呈正相关。热动力学系数取0.5时, 最适合热动力学模型预测3种实蝇在各实验温度LT_99.9968的致死时间。3种实蝇在44~47℃耐热性均为： 卵>1龄幼虫>3龄幼虫。番石榴实蝇在3种实蝇中最耐热。本研究结果为实蝇热处理指标的制定提供了实验依据。     

Experimental transmission of Leishmania tropica to hamsters and mice by the bite of Phlebotomus sergenti

Phlebotomus sergenti is a natural vector of Leishmania tropica. However, the ability of P. sergenti to transmit L. tropica by bite has not been proven experimentally yet. We have transmitted L. tropica to golden hamsters and BALB/c mice by the bite of P. sergenti. Sand flies and Leishmania both originated from an anthroponotic cutaneous leishmaniasis focus in Urfa, Turkey. P. sergenti females from a laboratory colony were infected by feeding on lesions of needle-inoculated hamsters or mice. Gravid females were allowed to refeed on uninfected hosts 9-15 d after the infective feeding. At the second feeding, some infected females took a full blood meal, while others only a partial one; some females failed to feed at all. The ability of infected females to take a blood meal did not correlate with the parasite transmissibility. In four BALB/c mice, lesions developed after 1-6 months. In two albino hamsters (Mesocricetus auratus), lesions developed 1 month after the infective feeding, and Leishmania could be reisolated from these sites. Another hamster did not develop a lesion; however, the feeding site and the adjacent ear were PCR positive 1 year after infective feeding. Our results show that dissemination to other parts of host body occurs in L. tropica after sand fly bite. Experimental transmission of the parasite confirms that P. sergenti is a natural vector of L. tropica.     

Microtopography of Nippostrongylus brasiliensis (Nematoda: Heligmosomatidae): Free-living larval stages

Microtopographic features of the various growth stages of the three free-living larval stages of the rat hookworm Nippostrongylus brasiliensis (Nematoda) were surveyed by scanning electron microscopy. These worms have a rounded anterior end and an elongated tail. Cuticular annulations were observed along the body, which also bore two ribbon-like lateral alae. Two rings of six lip-like lappets were observed around the triradiate oral opening in all larval stages. The cephalic space contained two lateral amphidial pits. The excretory pore in the third anterior part was observed in a ventral view of the larvae. No deirids were observed. The anus with a crescent-shape opening was located posteriorly. Phasmidial apertures, only observed in the third-stage larvae, opened on the lateral alae in the tail region. © 1993 Wiley-Liss, Inc.     

Microtopography of Nippostrongylus brasiliensis (Nematoda: Heligmosomatidae): Parasitic larval stages and adults

Specimens of the rat hookworm, Nippostrongylus brasiliensis (Nematoda) were recovered from lungs (third- and fourth-stage larvae) and intestine (fourth-stage larvae and adults). The following features were studied in the different stages by scanning electron microscopy: cephalic structures, especially sense organs, synlophe, cervical region, and caudal part. The main differences between the third and fourth stages concerned the lip-like structures around the oral aperture, the appearance of the cephalic space with the presence of a cephalic cap in fourth-stage larvae, the pattern of longitudinal ridges, and sexual differentiation. Pore-like papillae, not seen in third-stage larvae, developed in later stages. Deirids were observed only in adults, and phasmids were poorly discerned. Some of these morphological features, such as the cephalic sense organ apertures and cuticle pores and micropores, can be observed only by scanning electron microscop y. The possible functions of these different structures and their relationship with the behavior of the worms during their life cycle are discussed. © 1993 Wiley-Liss, Inc.     

异色瓢虫法国种群对豆蚜的捕食效应

异色瓢虫Harmonia axyridis(Pallas)的法国种群具有飞行能力较低的特点,在生物防治方面可能更具利用价值。为了使其更好的在田间应用,本文进行了异色瓢虫的法国种群各龄幼虫及雌、雄成虫对豆蚜的捕食功能比较研究。结果表明:各龄幼虫及雌、雄成虫对豆蚜捕食功能反应符合Holling II模型,检验各圆盘方程理论值和实测值拟合较好。同一虫态在不同空间水平对蚜虫的捕食能力有显著差异,在广口瓶处理中(较大空间),1～4龄幼虫及雌、雄成虫的最大理论捕食量分别为4.51、83.33、111.12、166.67、190及200头;不同虫期及成虫的瞬间攻击率a为3龄>4龄>雄虫>雌虫>2龄>1龄,且1龄的处理时间Th最长(0.2225);在培养皿处理中(较小空间),1～4龄幼虫及雌、雄成虫的最大理论捕食量分别为6.17、19.23、45.45、100、142.86、111.11头,不同虫期的瞬间攻击率a为2龄>3龄>雄虫>4龄>1龄>雌虫,且4龄的处理时间Th最长(0.1624)。     

Leishmania tropica in the black rat (Rattus rattus): persistence and transmission from asymptomatic host to sand fly vector Phlebotomus sergenti

Black rats (Rattus rattus) receiving Leishmania tropica injected intradermally into the ear were studied for the persistence of parasites and infectivity to natural sand fly vector. The mammalian host, the parasite, and the vector all originated from the endemic focus of Urfa, Turkey. Rats did not develop lesions or any apparent signs of disease, although at the site of inoculation they harboured live parasites capable of infecting sand flies. The number of L. tropica amastigotes detected in the inoculated ear by quantitative real-time PCR ranged from 5 x 10(3) to 10(6). Parasite DNA was also present in the tail and contralateral ear, sites distant from inoculation. After feeding on the ears of asymptomatic rats, Phlebotomus sergenti became infected with L. tropica. The average infection rate was 2.9%, and rats were infective for sand flies even 24 months post infection. The infectivity of the vertebrate host for insect vector was therefore not linked to the symptomatic stage of the infection. Such lack of correlation between clinical symptoms and infectivity to sand flies was reported previously for Leishmania infantum, the agent of visceral leishmaniasis; for species causing cutaneous leishmaniasis, however, this is the first evidence of transmission from a host without any visible cutaneous changes. If confirmed in the field, transmission from the asymptomatic host would be of great epidemiological significance.     

Immunohistological localization of serotonin in the CNS and feeding system of the stable fly Stomoxys calcitrans L. (Diptera: Muscidae)

Serotonin, or 5-hydroxytryptamine (5-HT), plays critical roles as a neurotransmitter and neuromodulator that control or modulate many behaviors in insects, such as feeding. Neurons immunoreactive (IR) to 5-HT were detected in the central nervous system (CNS) of the larval and adult stages of the stable fly, Stomoxys calcitrans, using an immunohistological technique. The location and pattern of the 5-HT IR neurons are described and compared for these two different developmental stages. Anatomical features of the fly feeding system were analyzed in third instar larvae and adult flies using a combination of histological and immunohistological techniques. In third instar larvae, the cibarial dilator muscles were observed within the cibarial pump skeleton and innervated by 5-HT IR neurons in nerves arising from the brain. There were four pairs of nerves arising from the frontal surface of the larval brain that innervate the cibarial pump muscles, pharynx, and muscles controlling the mouth hooks. A strong serotoninergic innervation of the anterior stomatogastric system was observed, which suggests 5-HT may play a role in the coordination of different phases of food ingestion by larvae. Similarly, many 5-HT IR neurons were found in both the brain and the thoracico-abdominal ganglia in the adult, some of which innervate the cibarial pump dilator muscles and the stomatogastric muscles. This is tnhe first report describing neuromuscular structures of the stable fly feeding system. The results reported here suggest 5-HT may play a critical role in feeding behaviors of stable fly larvae and adults.     

Comparison of Bloodmeal Digestion and the Peritrophic Matrix in Four Sand Fly Species Differing in Susceptibility to Leishmania donovani

The early stage of Leishmania development in sand flies is closely connected with bloodmeal digestion. Here we compared various parameters of bloodmeal digestion in sand flies that are either susceptible (Phlebotomus argentipes and P. orientalis) or refractory (P. papatasi and Sergentomyia schwetzi) to Leishmania donovani, to study the effects on vector competence. The volume of the bloodmeal ingested, time of defecation of bloodmeal remnants, timing of formation and degradation of the peritrophic matrix (PM) and dynamics of proteolytic activities were compared in four sand fly species. Both proven vectors of L. donovani showed lower trypsin activity and slower PM formation than refractory species. Interestingly, the two natural L. donovani vectors strikingly differed from each other in secretion of the PM and midgut proteases, with P. argentipes possessing fast bloodmeal digestion with a very high peak of chymotrypsin activity and rapid degradation of the PM. Experimental infections of P. argentipes did not reveal any differences in vector competence in comparison with previously studied P. orientalis; even the very low initial dose (2×103 promastigotes/ml) led to fully developed late-stage infections with colonization of the stomodeal valve in about 40% of females. We hypothesise that the period between the breakdown of the PM and defecation of the bloodmeal remnants, i.e. the time frame when Leishmania attach to the midgut in order to prevent defecation, could be one of crucial parameters responsible for the establishment of Leishmania in the sand fly midgut. In both natural L. donovani vectors this period was significantly longer than in S. schwetzi. Both vectors are equally susceptible to L. donovani; as average bloodmeal volumes taken by females of P. argentipes and P. orientalis were 0.63 μl and 0.59 μl, respectively, an infective dose corresponding to 1–2 parasites was enough to initiate mature infections.     

不同虫态及虫龄大草蛉与七星瓢虫之间的集团内互作

【目的】为明确新疆棉田棉蚜 Aphis gossypii 捕食性天敌之间的集团内捕食效应及其对蚜虫数量的控制作用。【方法】本研究以优势天敌昆虫大草蛉 Chrysopa pallens 和七星瓢虫 Coccinella septempunctata 为对象,以棉蚜为猎物,在温室中利用盆栽棉花,首先观察了2种天敌昆虫之间各虫态及虫龄配对的19个处理在无蚜植株上共存24 h后的存活数,然后观察了2种天敌昆虫配对处理下棉苗上棉蚜数量随时间的变化趋势。【结果】在无蚜棉株上2种捕食性天敌昆虫共存24 h后的存活结果表明：（1）在发育阶段相同的配对组合中,若是成虫则均存活,若是１龄幼虫则大草蛉存活较多,若是末龄幼虫则七星瓢虫存活较多;（2）在有卵的组配中,除七星瓢虫卵不被大草蛉成虫所捕食外,其他5个组配处理中卵均被捕食;（3）在有蛹的配对组合中,除七星瓢虫蛹被大草蛉末龄幼虫捕食外,其他处理下蛹均不被捕食;（4）在成虫与幼虫的配对组合中,七星瓢虫成虫捕食较多的大草蛉1龄幼虫,但不捕食大草蛉末龄幼虫,而大草蛉成虫与七星瓢虫1龄或末龄幼虫之间不发生捕食;(5）在不同龄期幼虫的配对组合中,大草蛉末龄幼虫捕食七星瓢虫1龄幼虫,而七星瓢虫末龄幼虫捕食大草蛉1龄幼虫。在有蚜植株上2种捕食性天敌共存对棉蚜数量具有不同的控制作用：（1）2种捕食昆虫的幼虫各自单独存在（对照）下,蚜虫密度随时间而降低;（2）大草蛉幼虫与七星瓢虫幼虫或成虫配对处理下,棉蚜密度随时间而增大;（3）大草蛉成虫与七星瓢虫幼虫或成虫配对处理下,棉蚜密度随时间而减小。【结论】研究结果说明,大草蛉与七星瓢虫之间存在集团内捕食,但２种天敌共存对棉蚜的控制作用取决于大草蛉虫态, 若大草蛉为幼虫,可使蚜虫密度增大,若为成虫,则使蚜虫密度减小。