Peculiarities of the brain organization and fine structure in small insects related to miniaturization. 2. The smallest Hymenoptera (Mymaridae, Trichogrammatidae)

The organization and fine structure of the brain in the smallest parasitic wasps, Anaphes flavipes and Trichogramma evanescens, were studied using serial histological sections as well as TEM and computer-assisted 3D reconstructions. The data on the number and size of neurons in the brain of Mymaridae and Trichogrammatidae were obtained. They confirm and supplement the hypothesis about the factors limiting miniaturization of insects. The organization of the brain of the smallest parasitic wasps is compared with that of Hemiptarsenus sp. (Eulophidae), a large representative of Chalcidoidea. Some brain areas reveal strong allometry. The relative volume of the antennal lobes, lateral protocerebrum, and protocerebral bridge increases significantly as the body size decreases. Miniaturization is accompanied by an increase in the relative brain volume and changes in the spatial orientation of some brain structures. The number and size of neurons of A. flavipes and T. evanescens are significantly different from those of large representatives of Chalcidoidea, but similar to those of other tiny insects. Miniaturization of the nervous system is limited by the size of neurons and the diameter of axons.     

Developmental stages of the hooded beetle Sericoderus lateralis (Coleoptera: Corylophidae) with comments on the phylogenetic position and effects of miniaturization

The first detailed morphological study of larvae, pupae and adults of a species of the hooded beetles (Coleoptera: Corylophidae) – Sericoderus lateralis – is presented. Histological sectioning, scanning and transmission electron microscopy, laser confocal microscopy and 3D-computer reconstruction were used. For the first time we report that according to the morphometric data of S. lateralis, at least some corylophid beetles have three larval stages. A phylogenetic position of Corylophidae within a cucujoid-cleroid clade is confirmed, and also the placement of Sericoderini within a corlyophid subgroup, which does not include Periptycinae and Foadiini. The larvae of Sericoderus are mainly characterized by plesiomorphic features compared to those of other corylophid tribes, notably Peltinodini and Rypobiini. Morphological and developmental consequences of miniaturization are discussed. Corylophid beetles display much less specific and far-reaching morphological consequences of miniaturization compared to Ptiliidae. We report the presence of unique modifications in the neural system not shared with any other insects, such as a distinctly asymmetric supraoesophageal ganglion in first instar larva, and a total displacement of the brain to the thorax in the adult stage. A highly unusual feature of the digestive tract is the sclerotised, V-shaped ventral wall of the pharynx. Developmental and size dependent changes in the relative volume of different organs are addressed. All organ systems change allometrically in the development of S. lateralis. Allometric trends in the volume of organs confirm that the factors limiting miniaturization are the size of the neural system, associated with the number and size of neurons (most critical for first instar larva), the mass of the skeleton, the egg size, and consequently the volume of the reproductive system (for free-living insects).     

Miniaturisation effects in larvae and adults of Mikado sp. (Coleoptera: Ptiliidae), one of the smallest free-living insects

We present the first morphological study of larvae and adults of Mikado sp. – one of the smallest known beetles and free-living insects (body length of adult is 390–455 μm). Morphological and developmental consequences of miniaturisation in Mikado and insects in general are discussed. We used histological sectioning, scanning electron microscopy, laser confocal microscopy and 3D-computer reconstruction. For the first time we report that according to the morphometric data of Mikado sp., at least some ptiliid beetles have three larval stages. We studied the muscular system of adults and larval stages. It is shown that ptiliid beetles have nearly the complete set of muscles found in larger staphyliniform beetles. Developmental and size dependent changes in the relative volume of different organs are addressed. All organ systems change allometrically in the development of Mikado sp. as well as in comparison with larger representatives of Ptiliidae and closely related groups of beetles, such as Staphylinidae. We conclude that the factors limiting miniaturisation are the size of the neural system, associated with the number and size of neurons, the mass of the skeleton, the egg size (free-living insects), and consequently the volume of the reproductive system.     

Anatomy of the smallest coleoptera, featherwing beetles of the tribe nanosellini (Coleoptera, Ptiliidae), and limits of insect miniaturization

The internal structure of Nanosella sp., Primorskella sp., and Porophila sp. was described from serial sections and total preparations using light and transmission electron microscopy. The most important structural features related to miniaturization are the absence of midgut muscles, abortion of two Malpighian tubes, a decrease in the number of abdominal spiracles, strong reduction of the tracheal system, the absence of the heart, reduction of the circulatory system and its substitution by the fat body, strong oligomerization and concentration of the nervous system, a decrease in the size and number of neurons, and reduction of the left testis and left ovary. The internal structure of featherwing beetles was analyzed for the first time using 3D computer models, which allowed us to demonstrate changes in the relative volume of organs accompanying the body diminution. The excretory and digestive systems change isometrically, while others change allometrically. The relative volume of the musculature decreases, and that of the nervous and reproductive systems increases. The skeleton mass also increases. The possible factors limiting further diminution in Ptiliidae (egg size, the volume of the reproductive and nervous systems, and the skeleton mass) are discussed.     

Peculiarities of the brain organization and fine structure in small insects related to miniaturization. 4. Thrips (Thysanoptera,Thripidae)

This article describes the morphology and ultrastructure of the brain of the greenhouse thrips, Heliothrips haemorrhoidalis (Thripidae), studied in a series of histological sections with the use of 3D reconstructions and TEM. The structural peculiarities of the brain organization and its features associated with body miniaturization as well as its quantitative characteristics (the number of cells and the volume of individual centers) are described for the first time in both the adult and the first-instar nymph of H. haemorrhoidalis. It is suggested that the limits of the nervous system miniaturization may be different in holo- and hemimetabolous insects.     

Extremely miniaturised and highly complex: The thoracic morphology of the first instar larva of Mengenilla chobauti (Insecta,Strepsiptera)

Thoracic structures of the extremely small first instar larva of the strepsipteran species Mengenilla chobauti (ca. 200 μm) were examined, described and reconstructed 3-dimensionally. The focus is on the skeletomuscular system. The characters were compared to conditions found in other insect larvae of very small (Ptiliidae) or large (Dytiscus) size (both Coleoptera) and features of “triungulin” larvae, first instar larvae of Rhipiphoridae, Meloidae (both Coleoptera), and Mantispidae (Neuroptera).The specific lifestyle and the extreme degree of miniaturisation result in numerous thoracic modifications. Many sclerites of the exo- and endoskeleton are reduced. Cervical sclerites, pleural ridges, furcae and spinae are absent. Most of the longitudinal muscles are connected within the thorax, and a pair of ventral longitudinal muscles is present in the pleural region of the meso- and metathorax. This results in a high intersegmental flexibility. Due to the size reduction and the correlated shift of the brain to the thorax, with 94 identified muscles the thoracic musculature appears highly compact. Compared to larger larvae the number of both the individual muscles and the muscle bundles are distinctly reduced. The thorax of the first instar larvae displays many additional strepsipteran autapomorphies. At least partly due to the highly specialised condition, potential synapomorphies with other groups were not found.     

Insect-induced wind pollination of the palm Chamaedorea pinnatifrons and pollination in the related Wendlandiella sp.

In Peruvian Amazonia pollination ecology of two palms, Chamaedorea pinnatifrons (Jacq.) Oerst. and Wendlandiella sp. was studied from October 1988 to January 1990. Both palms are dioecious understory species that form locally dense populations.In C. pinnatifrons both sexes flower synchronously during the dry season. Prior to anthesis, the pendulous male inflorescence is inhabited by numerous thrips (Thysanoptera) and Ptiliidae (Coleoptera). Staminate flowers open by a small basal slit between the petals. At anthesis pollen is shed and the movements of the insects inside the flowers trigger pollen release in small clouds. Thus, the powdery pollen becomes airborne and finally air currents act as a vector, carrying pollen to the inconspicuous female plants, which usually are not visited by insects. The term insect induced wind pollination is suggested for this pollination mode. Wendlandiella flowers during four months in the dry season. Male and female plants were not visited by insects. The dry condition of the pollen indicates that anemophily is the pollination mode in Wendlandiella. Fructification is rare but the plants show intense vegetative propagation.The significance of anemophily in the tropical lowland rain forest is discussed.     

A new species description of the acanthomus species group (Acari: Podapolipidae: Eutarsopolipus), with keys to world species of the group

Mites of the family Podapolipidae (Acari: Heterostigmatina) are permanent parasites of insects. During an intensive survey of insect parasitic mites in Iran, a new species of the genus Eutarsopolipus Berlese, 1911 (Acari: Heterostigmatina: Podapolipidae), belonging to the acanthomus species group, was found from the subelytra of Amara (Amara) aenea (De Geer, 1774) (Coleoptera: Carabidae). In this article, Eutarsopolipus amaraceus Tajodin and Hajiqanbar sp. nov. is described and compared with the most closely related species. In addition, keys to world species of all stages of the acanthomus group are provided, and the host range of all representatives of the group is discussed.     

Discheramocephalini,a new pantropical tribe of featherwing beetles (Coleoptera: Ptiliidae): description of new taxa and phylogenetic analysis

Abstract Two new genera and eight new species of featherwing beetles (Coleoptera: Ptiliidae) possessing a remarkable horizontal perforation of the mesoventral keel are described: Skidmorella vietnamensis sp.n. (Vietnam), S. memorabilis sp.n. (Indonesia), S. serrata sp.n. (Vietnam), Fenestellidium capensis gen. et sp.n. (South Africa, type species), F. kakamegaensis sp.n. (Kenya), Cissidium okuensis sp.n. (Cameroon), Dacrysoma usambarensis gen. et sp.n. (Tanzania, type species) and D. felis sp.n. (Madagascar). A phylogenetic analysis of 24 taxa and 37 parsimony‐informative characters supports the hypothesis of a single origin of the mesoventral perforation, thus uniting Discheramocephalus, Skidmorella, Africoptilium, Fenestellidium, Cissidium and Dacrysoma into a pantropically distributed clade, for which a new tribe Discheramocephalini (type genus Discheramocephalus) is proposed. Identification keys to Discheramocephalini genera and, in some cases, to species are provided. Each new species is illustrated with scanning electron microscopy images.     

The reproductive biology of Nelumbo pentapetala (Nelumbonaceae) on the Upper Mississippi River. II. The insects associated with the transfer of pollen

An in-depth study of the insects associated with the transfer of pollen in the American lotus was undertaken in a selected population on the Upper Mississippi River near La Crosse, Wisconsin. The study showed that members of the Coleoptera (Coleomegilla fascilabris Malsant, Diabrotica unidecimpunctata howardi Barber, D. virgifera Lec.), Diptera (Eristalis tenax (L.), Parhelophilus laetus (Locw)) and Hymenoptera (Agapostemon radiatus (Say), Apis mellifera L., Dialictus sp., Lasioglossum zonulum (Smith)) were the principal visitors and most obvious vectors in pollination. Although there are features of the flowers of the lotus that indicate cantharophily, such as the diurnal movements of the tepals and the food bodies of the anthers, in the area of study no special beetle-pollination system, as reported for such genera as Magnolia and Nuphar, appears to occur.     

Morphological and taxonomical novelties in the world's smallest beetles, and the first Old World record of Nanosellini (Coleoptera: Ptiliidae)

Baranowskiella ehnstromi gen.n. and sp.n. of the featherwing beetle tribe Nanosellini (Coleoptera: Ptiliidae), the smallest beetles of all, is described from Sweden. This is the first record of the tribe from the Old World. The holomorphology of Baranowskiella is commented upon and analysed in relation to other nanoselline genera. Several characters previously not known or considered in ptilid or staphylinoid taxonomy are introduced, including the morphology of the elytral venter and metanotum. The surprising occurrence of mesocoxal mycangia and a venteroelytral-metepimeral stridulatory mechanism in Nanosellini, unique among Ptiliidae and previously unknown in Staphylinoidea, is possibly correlated with adaptation to life in bracket fungus pores.     

The complete mitochondrial genome of the intertidal copepod Tigriopus sp. (Copepoda, Harpactidae) from Korea and phylogenetic considerations

This paper reports on the basic characteristics of the mitochondrial genome of the intertidal copepod Tigriopus sp. from Korea, including its structural organization, base composition of rRNAs and protein-encoding genes, and the secondary structure of tRNAs. We amplified the complete mitochondrial DNA of the intertidal copepod Tigriopus sp. from Korea (sampling site Busan) by long-polymerase chain reaction (long-PCR) with conserved primers and sequenced this mitogenome by primer walking using flanking sequences as sequencing primers. The primer informations were obtained as expressed sequence tags (ESTs) from Tigriopus sp. The resultant Tigriopus sp. mitochondrial DNA sequence was 14,301 bp with a conserved structural organization, compared to that of T. japonicus from Japan with significant differences in several protein-coding regions including rRNAs, although the genomic organization of the mitochondrial genome was identical. In order to investigate biogeographic differences within the genus Tigriopus, we analyzed the CO1 gene by sequencing. This way, we compared several Tigriopus species from Korea, Japan, Hong Kong and Taiwan as well as other related species such as T. californicus, T. brevicornis and T. fulvus. The results further support the notion that the copepods display significantly different genomes within the same genus. These findings provide valuable genomic information for further studies on the population genetics and speciation processes within the genus Tigriopus.     

Antimicrobial peptides isolated from insects and their potential applications

Antimicrobial peptides (AMPs) in insects have the potential to be developed as chemotherapy agents against numerous microbial species. This article reviewed the existing knowledge of what have been focused so far on published materials related to AMPs isolated from insects. Previous studies were focused on peptide characterization and the mechanism pathways of different AMPs from a variety of insect Orders. Most studied insect Orders are as follows: Hymenoptera (50%), Diptera (17%), Coleoptera (13%), Lepidoptera (10%), Hemiptera (5%), Blattodea (3%) and Odonata (2%). Dozens of new AMPs have been extracted from insects recently. However, more studies in vivo and in vitro are necessary to fully understand their effect and the mechanisms of antimicrobial action to utilize their promising potential in cosmetic and pharmaceutical industries.     

The thoracic skeleto-muscular system of Mengenilla (Strepsiptera: Mengenillidae) and its phylogenetic implications

The thorax of Mengenilla was examined using traditional morphological techniques and its features were documented in detail using scanning electron microscopy and computer-based 3D reconstructions. The results were compared to conditions found in other holometabolan insects. The implications for the systematic placement of Strepsiptera are discussed. The observations are interpreted in the light of the recently confirmed sistergroup relationship between Strepsiptera and Coleoptera (Coleopterida). The synapomorphies of the thorax of Strepsiptera and Coleoptera are partly related with posteromotorism (e.g., increased size of the metathorax), partly with a decreased intrathoracic flexibility (e.g., a fused pronotum and propleurum), and partly independent from these two character complexes (e.g., not connected profurca and propleuron). Strepsiptera are more derived than Coleoptera in some thoracic features (e.g., extremely enlarged metathorax) but have also preserved some plesiomorphic conditions (e.g., tegulae in both pterothoracic segments). All potential apomorphies of Mecopterida are missing in Strepsiptera. The last common ancestor of Coleopterida had already acquired posteromotorism but the wings were still largely unmodified. Several reductions in the mesothorax likely occurred independently.     

Features of the structure of hymenoptera associated with miniaturization: 2. Anatomy of <Emphasis Type="Italic">Trichogramma evanescens</Emphasis> (Hymenoptera,Trichogrammatidae)

Anatomy of adults of Trichogramma evanescens (Hymenoptera: Trichogrammatidae) is described in detail for the first time based on series of sections and 3D computer reconstruction. The complex structure of the exoskeleton and musculature (except for reductions of individual muscles) is preserved in T. evanescens despite its tiny size. Considerable simplification is observed in the structure of the intestine, tracheal and circulatory systems, and in the reduced number of Malpighian tubules. Thus, the smallest Hymenoptera (Mymaridae and Trichogrammatidae) demonstrate both the effects of miniaturization universal for insects (reduction of the head endoskeleton, circulatory and respiratory systems) and specific ones.     

Distribution and fine structure of antennal olfactory sensilla in Japanese dung beetles,Geotrupes auratus Mtos. (Coleoptera : Geotrupidae) and Copris pecuarius Lew. (Coleoptera : Scarabaeidae)

The distribution and fine structure of olfactory sensilla on the antennal flagella of the Japanese dung beetles, Geotrupes auratus (Coleoptera : Geotrupidae) and Copris pecuarius (Coleoptera : Scarabaeidae) were studied by scanning and transmission electron microscopy. In both types of dung beetles, sensilla on the antennal segments were most abundant on the apical 3 lamellar segments, where sensilla basiconica were particularly concentrated. The sensilla were solely concentrated in the central part of the distal side of both the 9th and 10th segments in G. auratus and the 7th and 8th segments in C. pecuarius, respectively. The numbers of sensilla in these areas (channels) of the 9th and 10th segments in G. auratus were approximately 4,500 and 3,000, respectively. In C. pecuarius, there were about 1,900 sensilla on the 7th segment and l,700 sensilla on the 8th. The cuticles of the sensilla in both species were perforated by numerous elongate pores, with a pore density of about 45/ μm² in G. auratus and 30/ μm² in C. pecuarius. Each sensillum basiconicum in C. pecuarius was generally associated with 2 sensory neurons. The sensory cilia passed into the sensillum lumen and branched profusely, occupying most of its space. On the basis of the fine structure and dense location, these sensilla are considered to have an olfactory function for food detection.     

Larval head morphology of Hydroscapha natans (Coleoptera, Myxophaga) with reference to miniaturization and the systematic position of Hydroscaphidae

 The head of third instar larvae of Hydroscapha natans was reconstructed three dimensionally on a computer. This technique allowed a detailed examination and presentation of internal features of a representative of the ’suborder’ Myxophaga, which is characterized by the very small size of the immature stages and adults. Larval character states of H. natans were compared with features found in other representatives of the Coleoptera. The monophyly of the Myxophaga (excluding Lepiceridae) is supported by several autapomorphies of the larval head: a broadened, transverse head, scale-like cuticular surface structures, round and flattened labral sensilla, short antennae with only two antennomeres, a ligula with papillae, and a broadened tentorial bridge. A monophylum comprising the Hydroscaphidae and Microsporidae is characterized by a very unusual semientognathous condition of the mouthparts and an unusual shape and large relative size of the brain. The last common ancestor of the Hydroscaphidae, Torridincolidae, and Microsporidae was probably living in hygropetric habitats. Several apomorphies have evolved in correlation with this peculiar life style. The very dense arrangement of muscles and other internal structures, and the unusual shape and size of the cerebrum have resulted from miniaturization. The overall complexity of the head is not reduced in comparison to larvae of other representatives of Coleoptera. A negative allometric relationship between body size and the size of the brain, and a correlation between brain size and the size of neurons was found in several species of Coleoptera examined. Accepted: 16 December 1997     

Marine Nematodes of Bothnian Bay,Finland: Ethmolaimus hailuotoensis n. sp. (Ethmolaimidae: Nemata)

Ethmolaimus hailuotoensis n. sp. from Bothnian Bay, northern Baltic Sea, is described and illustrated. Ethmolaimus hailuotoensis n. sp. has a strongly sclerotized luminal lining of the terminal esophageal bulb and esophagus. The most characteristic feature is a lateral series of large concentric, sclerotized rings with a fine, internal longitudinal oval sclerotization. In addition, E. hailuotoensis n. sp. is distinguished from other Ethmolaimus species by its smaller body size, fewer number of precloacal supplements (7-8), conical tail, and the position of amphid posterior to the buccal cavity. Females of E. hailuotoensis n. sp. studied were hermaphroditic. Ethmolaimus hailuotoensis n. sp. coexisted with E. pratensis. Ethmolaimus pratensis from Bothnian Bay has a characteristic row of sublateral hypodermal glands, a character not before seen in Ethmolaimidae.     

Reproductive Biology of the Monoecious Understory Palm Prestoea schultzeana in Amazonian Ecuador1

Prestoea schultzeana is a monoecious, protandrous palm in the forest understory of Amazonian Ecuador. We studied its leaf production, population density, sexual expression, phenology, pollination, and the specificity of the floral visitors. On average, 1.4 leaves and 0.9 inflorescences are produced per individual per year. The number of staminate flowers per inflorescence is relatively constant compared with the number of pistillate flowers which varies greatly. Flowering occurs in staminate and pistillate phases of approximately 19 and 0–7 days duration, respectively. Flowers open in the morning, and staminate flowers abscise in the afternoon of the same day whereas pistillate flowers last for two days. Flowers are whitish-yellow with a sweet odor and produce nectar. They were visited by Coleoptera (Chrysomelidae, Curculionidae, Nitidulidae, Ptiliidae, Staphylinidae), Hemiptera, Diptera (Drosophilidae, Syrphidae, Ceratopogonidae), Lepidoptera (Nymphalidae), and Hymenoptera (Formicidae, Halictidae). All examined individuals of the syrphid fly Copestylum sp. visiting pistillate flowers carried 100–500 grains of P. schultzeana pollen. Pollen occurred on all body parts, but especially on the legs, and this makes Copestylum sp. the most important pollinator. Most floral visitors were also frequent on the flowers of co-occurring plant species; notably the palm Hyospathe elegans shared most visitor species with P. schultzeana.