Evolutionary relationships of flavobacterial and enterobacterial endosymbionts with their scale insect hosts (Hemiptera: Coccoidea)

Flavobacteria and Enterobacteriaceae have been previously reported as scale insect endosymbionts. The purpose of this work was twofold: first, to screen different scale insect families for the presence of these endosymbionts by PCR analyses and second, to elucidate the history of cophylogeny between these bacteria and the insects by analysing a portion of 16S rRNA and 18S rRNA gene sequences by two reconciliation tools, CoRe‐PA and Jane. From a survey of 27 scale insects within seven families, we identified Flavobacteria and Enterobacteriaceae as coexisting in ten species that belong to the Ortheziidae, Monophlebidae, Diaspididae and Coccidae families, and we frequently found two closely related enterobacteria harboured in the same individual. Analyses performed with CoRe‐PA and Jane suggest that Flavobacteria from the scale insects analysed have a unique origin, except for Candidatus Brownia rhizoecola (Flavobacteria of Pseudococcidae, Phenacoccinae), which seems to come from a nonscale insect. Nevertheless, cospeciation between Flavobacteria and scale insects is suggested only within the families Monophlebidae, Ortheziidae and Diaspididae, and host switches seem to have occurred from the ancestors of Monophlebidae and Ortheziidae to insects from families Coccidae, Lecanodiaspididae, Eriococcidae and Pseudococcidae. Our analyses suggest that Enterobacteriaceae underwent more evolutionary events (losses, duplications and host switches), and their phylogenies showed a lower proportion of congruent nodes between host and bacteria, indicating a more relaxed relationship with scale insects compared with Flavobacteria.     

滇川桂3省暗褐网柄牛肝菌菌腔虫瘿的寄主植物与介壳虫种类调查

暗褐网柄牛肝菌Phlebopus portentosus与介壳虫形成的菌腔虫瘿是该菌营养机制研究的关键环节。本研究先后在云南、四川和广西3省区暗褐网柄牛肝菌产区的16个地点,对菌腔虫瘿的生态和生物学进行了大量的野外调查。发现根部着生菌腔虫瘿的寄主植物有31种,涉及16个科的28个属。与暗褐网柄牛肝菌形成菌腔虫瘿的介壳虫种类有12种,其中10种隶属粉蚧科Pseudococcidae、绵蚧科Monophlebidae、蚧科Coccidae各1种。在不同的寄主植物上菌腔虫瘿的寄生位置和形状会有所不同,与暗褐网柄牛肝菌菌丝形成菌腔虫瘿的寄主植物和介壳虫之间不存在专一性。上述研究结果为暗褐网柄牛肝菌的仿生栽培奠定了基础。     

The ovaries of scale insects (Hemiptera, Coccinea). Morphology and phylogenetic conclusions

Coccoids (Coccinea, Coccoidea, Coccomorpha, scale insects, scales) are a highly diverse group of ectoparasitic insects. They comprise 2 subgroups: primitive archaeococcoids (= Orthezioidea sensu Koteja) and advanced neococcoids (= Coccoidea sensu Koteja). The ovaries of coccoids consist of numerous short telotrophic-meroistic ovarioles. The ovarioles of all investigated species share common characters (e.g. the same mechanism of ovariole development, lack of terminal filaments, occurrence of single oocytes in the vitellaria) supporting the concept of monophyletic origin of this group. Despite these characteristics, the ovaries of archaeococcoids and neococcoids differ in the number of germ cells (oocytes + trophocytes) constituting a single ovariole. In primitive families (Ortheziidae, Margarodidae), this number is relatively large (15-58), whereas in advanced ones (Pseudococcidae, Kermesidae, Eriococcidae, Cryptococcidae, Coccidae, Diaspididae) it is small and usually does not exceed 8. The comparative analysis of the ovary structure in the representatives of Coccinea and closely related Aphidinea (aphids) has revealed that: (1) the organization of archaeococcoid ovaries is more similar to those of aphids than to neococcoids and (2) during the evolution of Coccinea a gradual reduction in the number of germ cells in ovarioles took place.     

Genetic basis of encapsulation response in Anopheles gambiae

The phenomenon of encapsulation of invading organisms is widespread in insects. Co-evolution has produced an intricate balance between the immune responses of the host and immune-suppressive (or immune-evading) properties of the parasite. Genome-wide genetic mapping revealed different loci in Anopheline mosquitoes were involved in melanotic encapsulation of different malaria parasites. Certain isolates of human malaria parasites can still suppress or avoid the immune response from refractory mosquitoes. Similar interactions with parasitoids were observed in Drosophila melanogaster. Species-specific encapsulation locus was identified for two parasitoids, respectively, and virulent strain of parasitoid can suppress the immune system of an otherwise resistant fruitfly. It is believed that the encapsulation loci in both mosquitoes and fruitfly may encode gene products that function at the early stages of parasite/parasitoid recognition or immediate signaling events. Future research on membrane receptor molecules and their roles in insect immunity will yield interesting insights into mosquito-parasite interactions.     

Cardinium in Plagiomerus diaspidis (Hymenoptera: Encyrtidae)

The bacterial symbiont Cardinium (Bacteroidetes) was previously implicated in the thelytokous reproduction of the parasitoid Plagiomerus diaspidis Crawford (Hymenoptera: Encyrtidae). Horizontal transmission of the symbiont among the cactus scale Diaspis echinocacti Bouché (Homoptera: Diaspididae) and its hymenopteran parasitoids has been suggested. In this study, the bacteria associated with D. echinocacti, its parasitoids P. diaspidis and Aphytis sp. (Hymenoptera: Aphelinidae), and the hyperparasitoid Marietta leopardina Motschulsky (Hymenoptera: Aphelinidae) were characterized using molecular fingerprinting techniques, and the localization of Cardinium in P. diaspidis was studied using fluorescence in situ hybridizations (FISH). Cardinium was the only bacterium found in P. diaspidis, but it could not be detected in any of the other insects tested. The symbiont was specifically located in the reproductive tissues of its P. diaspidis host.     

Effects of temperature and host age upon the encapsulation of Metaphycus stanleyi and Metaphycus helvolus eggs by brown soft scale Coccus hesperidum

Encapsulation of eggs inserted by Metaphycus stanleyi (Hymenoptera: Encyrtidae) into the brown soft scale Coccus hesperidum (Homoptera: Coccidae) became more frequent as the host matured. This occurred with both laboratory reared and field-collected parasites. After parasitism for 24 hr at 27°C, encapsulation frequency did not differ in hosts reared at 20° or at 27°C, but significantly increased in hosts reared at 33°C. When parasitism and rearing were carried out at the same temperature, the percentage of eggs encapsulated increased from 48.7% at 27°C to 94.1% at 33°C. With M. helvolus, the percentage of eggs encapsulated was considerably higher than with M. stanleyi; e.g., 99.3 vs 48.7%, respectively, at 27°C. At 20° and 27°C, some M. helvolus development occurred in the larvae of brown soft scale but none at 33°C; the adult stages of the host encapsulated all the parasite eggs at these temperatures.     

Further studies of the encapsulation of eggs ofMetaphycus spp. (Hym.: Encyrtidae) by the pyriform scale,Protopulvinaria pyriformis (Hom.: Coccidae)

The encapsulation of eggs ofMetaphycus swirskii Annecke &; Mynhardt (Hymenoptera: Encyrtidae) by the pyriform scale,Protopulvinaria pyriformis (Cockerell) (Homoptera: Coccidae), collected in the coastal plain of Israel, was determined during April 1986 to May 1987. The rates of encapsulation were low in November (13.0%) and relatively high in April, May, August and September (32.0–89.0%). The seasonal variations in the encapsulation of eggs ofM. stanleyi Compere and/orM. swirskii byP. pyriformis infesting avocado (Persea americana) and jambolan (Syzygium cumini) were studied at Miqwe Yisra'el (coastal plain) during October 1986 to February 1988. Encapsulation rates were similar in scales infesting either of the two host plants. They were highest during July to August (49.0–75.0%) and lowest during December to February (0.9–10.0%). Encapsulation incidence at Miqwe Yisra'el was correlated with the ambient temperatures (r=0.89). The rate of encapsulation of parasitoid eggs (M. stanleyi and/orM. galbus Annecke) recorded inP. pyriformis sent to Israel from Spain in September 1987 was 42.2%. The high rates of encapsulation ofMetaphycus spp. eggs byP. pyriformis during the summer, may interfere with efficient biological control of the pest.     

Relationships between parasitoid host range and host defence: a comparative study of egg encapsulation in two related parasitoid species

Abstract. Parasitoid host range may proceed from traits affecting host suitability, traits affecting parasitoid foraging behaviour, or both. We tested the hypothesis that encapsulation can be used as a reliable indicator of parasitoid host range in two closely related larval endoparasitoids of Lepidoptera. Cotesia glomerata (L.) (Hymenoptera: Braconidae) is gregarious and a generalist on several species of Pieridae, whereas C. rubecula (Marshall) is solitary and specific to Pieris rapae (L.). We determined the effects of host species ( Pieris brassicae (L.), P. napi (L.) and P. rapae ) (Lepidoptera: Pieridae) and host developmental stage (early first, second and third instar) on encapsulation of parasitoid eggs. Host species and parasitoid species, as well as the resulting interaction between these two factors had significant effects on encapsulation of Cotesia eggs. Encapsulation in Pieris hosts was much lower for C. glomerata (<34%, except for second and third instar of P. rapae ) than for C. rubecula (>32%), even when the latter was parasitizing P. rapae. Encapsulation increased with the age of the larvae, although the only significant difference was for C. glomerata. Overall, P. rapae showed a stronger encapsulation reaction than P. brassicae and P. napi. Encapsulation levels of C. glomerata corresponded well to patterns of female host species and host age preference for oviposition and parasitoid larval performance. In contrast, percentages of encapsulation of C. rubecula were not consistent with host preference and host suitability. We argue that encapsulation alone is unlikely to provide a sufficient explanation for C. glomerata and C. rubecula host range.     

白蜡绵粉蚧血细胞的显微形态与超微结构观察

为研究蚧虫血淋巴中血细胞的种类及其结构特征,本文采用荧光显微镜、扫描电镜和透射电镜观察了白蜡绵粉蚧Phenacoccus fraxinus Tang(半翅目:蚧总科:粉蚧科)雌成虫血细胞的显微形态超微结构.结果显示,在荧光显微镜和扫描电镜下观察识别出白蜡绵粉蚧血淋巴中的5种血细胞,即原血胞、浆血胞、粒血胞、类绛色血胞和囊血胞.在透射电镜下,原血胞的细胞核明显,表现出高的细胞质密度;浆血胞最典型的特征是细胞质中有大量的囊泡;粒血胞的细胞质中有发达的粗面内质网和许多玫瑰形的细颗粒;类绛色血胞最典型的特征是有许多结晶,并在细胞质空泡区内分布更多;囊血胞透明性强,具有围核空间,膨大成潴泡状.     

Structure of a herbivore–parasitoid community: Are parasitoids shared by different herbivore guilds?

Plant–herbivore–parasitoid interactions are a common occurrence in terrestrial food webs. Few parasitoids are thought to be shared by host insects of different feeding guilds because different parasitism strategies are required to use hosts of different feeding types. However, this assumption has rarely been tested using data from nature. To clarify whether parasitoids are shared among host guilds, I examined the structure of parasitoid communities on herbivore guilds associated with two Rhododendron species (Ericaceae) in a temperate secondary forest in central Japan. Leaf- and flower-feeding insects were collected from Rhododendron reticulatum and Rhododendron macrosepalum shrubs and reared in the laboratory for 3 years from April 1999 to March 2002. In total, 79 species of holometabolous herbivores (Lepidoptera, Diptera, Coleoptera, and Hymenoptera) were recorded, with 62 species on R. reticulatum and 51 species on R. macrosepalum. A total of 81 parasitoid species (Hymenoptera and Diptera) was recorded from the sampled herbivores, with 48 species from those on R. reticulatum and 50 species from those on R. macrosepalum. In total, 36 herbivore species were parasitised by 1–18 parasitoid species per host species, although the number of parasitoid species was strongly affected by sample size. Parasitoids that had two or more host species frequently attacked herbivore species from different families or on different host plants, whereas they did not attack species from different herbivore guilds; no parasitoids were shared between external feeders and rollers. Therefore, my results support the hypothesis that few parasitoids are shared among herbivores of different feeding guilds.