Development of the bitterling,Tanakia tanago (cyprinidae), with a note on minute tubercles on the skin surface

The development of eggs and larvae and minute tubercles on the skin surface in larvae ofTanakia tanago were observed. The eggs began to hatch approximately 52 hours after insemination and the larvae reached free-swimming stage 19 days after hatching at water temperature of 22±1°C. The egg and larval development and minute tubercles on the skin surface in larvae of this species were similar to those ofAcheilognathus lanceolata andA. limbata. However,T. tanago was distinguishable in egg and larval development fromA. lanceolata andA. limbata by the following characters: the perivitelline space was narrower, embryonic and larval development was faster, and minute tubercles on the skin surface of the anteriormost parts of the yolk sac, and of the body and head were hemispheric in shape. From these characters,T. tanago is considered to be more specialized thanA. lanceolata andA. limbata.     

Minute tubercles on the skin surface of larvae in the Korean endemic bitterling, Rhodeus pseudosericeus (Pisces, Cyprinidae)

The morphology and distribution of the minute tubercles on the skin surface of larvae in Korean bitterling, Rhodeus pseudosericeus, were observed during larval development. Just after hatching, the epidermis of the larvae consists of a thin single cell layer having smaller basophilic flat or round‐flattened basal cells. As the larvae grow, the epidermis contains more small flat cells and large epidermal cells that are round or hemisphere‐shaped. These large unicellular epidermal cells, called minute tubercles, consist of more or less homogeneous cytoplasm that is PAS (Periodic acid‐Schiff method) positive. They are more densely distributed in the wing‐like yolk sac projection. Vestigial minute tubercles occur in the body region and the caudal fin‐fold region. These minute tubercles grow in number and height from 6 to 8 days after hatching onward. However, they become reduced in height and number as the larvae develop. At day 31 after hatching (i.e. free‐swimming stage), minute tubercles no longer exist on the larval skin. The sequence of occurrence and gradual disappearance of these cell structures are described and histologically documented for comparative purposes of beta, taxnomomic and environmental studies.     

Fruit trap: A detection and collection tool for opiine parasitoids (Hym.: Braconidae) of the oriental fruit fly,Bactrocera dorsalis (Dipt.: Tephritidae)

A fruit trap was developed for detection and collection of the opiine parasitoids of the oriental fruit fly,Bactrocera (=Dacus)dorsalis (Hendel). Gravid females ofBiosteres arisanus (Sonan), an egg-larval parasitoid, orDiachasmimorpha longicaudata (Ashmead) andPsytallia incisi (Silvestri), both larval parasitoids, were lured to parasitize the eggs or larvae ofB. dorsalis inoculated in ripe papaya fruits,Carica papaya L. Progenies ofB. arisanus were consistently recovered from papaya fruits inoculated withB. dorsalis eggs (subsequently referred to as egg fruit traps). Except in Moloaa on Kauai (6%), higher percentage ofB. dorsalis parasitization (range=38–43%) was recorded in Hilo, island of Hawaii and Waimanalo and Poamoho, island of Oahu. Progenies ofD. longicaudata and a fewP. incisi were recovered from papaya fruits artificially infested withB. dorsalis larvae (subsequently referred to as larval fruit traps). The recovery of parasitoid progenies from larval fruit traps suspended from papaya trees did not differ significantly from larval fruit traps placed on the ground. In both methods of trap placement, percent parasitization ofB. dorsalis byD. longicaudata (predominant species) ranged from 58–60%. On the other hand, significantly moreB. arisanus thanD. longicaudata andP. incisi adults (larval parasitoids) were recovered from fully ripened to highly deteriorated papaya fruits collected from papaya trees or ground (fallen fruits).     

Intestinal morphology in oily bitterlings (Cyprinidae: Acheilognathinae)

We evaluated inter- and intraspecific variations of the intestinal coiling patterns and intestinal length of the oily bitterlings, Tanakia limbata, Tanakia koreensis, Tanakia somjinensis, and Tanakia signifer. All the oily bitterling species shared a unique intestinal coiling pattern, expressed as an oval shaped loop. The ratio of the intestinal length to standard length varied among species, viz., both T. koreensis and T. signifer have significantly longer intestines than T. limbata and T. somjinensis. The intestinal length may be a useful diagnostic character between two sibling species, T. koreensis and T. somjinensis, although we observed intraspecific variation in the intestinal length of T. limbata and T. koreensis among collection sites.     

Minute tubercles in bitterling larvae: Developmental dynamic structures to prevent premature ejection by host mussels

1. Bitterlings are small freshwater fish that use long ovipositors to lay eggs in host mussels, and they have morphological adaptations to increase larval survival. The most well‐known adaptation is the minute tubercles on the skin surface of larvae; they are developed in early‐stage larvae with weak swimming ability and disappear in free‐swimming larvae before they leave the host mussel.
2. In the present study, I comprehensively analyzed the developmental stages of Rhodeus pseudosericeus larvae, their morphological and physiological characteristics, their migration inside mussels, and the development of minute tubercle in order to elucidate the morphological function of the minute tubercles. These tubercles began to develop 1 day after hatching (formation stage), grew for 2–5 days (growth stage), reached the peak height after 6–7 days (peak stage), abruptly reduced in height after 8–10 days (abrupt reduction stage), and gradually reduced in height (reduction stage) until completely disappearing 27 days after hatching (disappearance stage).
3. The larvae remained in the mussels’ interlamellar space of the gill demibranchs until 10 days after hatching and began to migrate to the suprabranchial cavity 11 days after hatching. At this time, the larvae had a heart rate and the caudal fin began to develop. At 24 days after hatching, the minute tubercles had almost disappeared, and some individuals were observed swimming out of the mussels.
4. The results presented herein elucidate that the minute tubercles are the developmental dynamic structures that the bitterling larvae have morphologically adapted to prevent premature ejection from the mussel.

     

Laboratory evaluation of predation on mosquito larvae by Australian mangrove fish

A series of laboratory experiments compared predation rates of three native eastern Australian mangrove fish species (Psuedomugil signifer, Hyseleotris galii, Pseudogobius sp.) and the exotic Gambusia holbrooki on 2^nd and 4^th instar Aedes vigilax larvae, in order to determine their potential as mosquito control agents in mangrove forests. All four species preyed on significant numbers of both 2^nd and 4^th instar larvae. All showed a similar pattern of larval consumption, gorging on larvae in the first hour of each experiment, before reducing to a relatively constant background feeding rate. Gambusia holbrooki showed the highest larval consumption rates, but is unsuitable as a mosquito control agent due to it being an exotic pest species in Australia. Of the three native species, P. signifer showed the greatest potential as a mosquito control agent, having consumption rates comparable to G. holbrooki, and was the only species that did not show a significant reduction in larval consumption in the night experiments.     

Embryonic and larval development of a Japanese spinous loach,Cobitis takatsuensis

The embryonic and larval development ofCobitis takatsuensis, a mountain stream spinous loach, was surveyed by incubating artificially inseminated eggs. The mean diameter of the inflated eggs and mean total length of newly-hatched larvae were 2.7 mm and 5.7 mm, respectively. The eggs were spherical, transparent and unpigmented, with a pale yellow yolk and no oil globule. The daily cumulative temperature to hatching was estimated to be 70–110°C. day. Hatched larvae were unpigmented with outer gill filaments on their cheeks, as in otherCobitis species, but the melanophores were comparatively less obvious at each developmental stage. The larvae started feeding eleven days after hatching yolk absorption being completed sixteen days after hatching. All the fin rays were fully developed and the juvenile stage reached at 16 mm TL, 38 days after hatching. Embryonic and larval developmental traits ofC. takatsuensis, such as egg size, clutch size and larval pigmentation, were similar to the Korean species,Niwaella multifasciata, that lives in the upper reaches of the Nak-tong river, andN. delicata, which inhabits Japanese mountain streams, rather than to its congeners. Among cobitine fishes, the spawning of a small number of larger eggs yielding larger larvae without pigmentation, characteristics shared byC. takatsuensis, N. multifasciata andN. delicata, is attributable to adaptation to cold mountain streams.     

The consequences of egg cannibalism inAdalia bipunctata [Coleoptera: Coccinellidae]

When eggs ofAdalia bipunctata L. are offered to larvae of their own species, these larvae are able to develop to adults. Reducing the daily egg supply results in decreased larval survival and pupal weight and especially fecundity of the adult females. The duration of larval development is significantly increased, the longevity of adults is shortened.     

Pharyngeal teeth and masticatory process of the basioccipital bone in Japanese bitterlings (Cyprinidae)

The pharyngeal teeth and the masticatory process of the basioccipital bone were compared in fifteen species and subspecies of Japanese bitterlings.Acheilognathus lanceolata, A. limbata and two subspecies ofRhodeus ocellatus, which are characterized by the absence of serrations on the side of the pharyngeal teeth, have reduced occlusal grooves on the pharyngeal teeth. In the larvae of these species, the occlusal grooves are fairly developed. The occlusal grooves of the adult pharyngeal teeth in herbivorous species are more developed than those in omnivorous species. The occlusal grooves seem to have developed in relation to the feeding habits. On the basis of the combination of developmental degrees of the anterior part of the masticatory process, the occlusal grooves and the chewing area on the pharyngeal first tooth, Japanese bitterlings were classified into two groups and two types and/or five subtypes, suggesting phylogenetic relationships among them.     

Evidence for the reproductive isolation ofDermacentor marginatus andDermacentor reticulatus (Acari: Ixodidae) ticks based on cross-breeding, morphology and molecular studies

The species status ofDermacentor marginatus andDermacentor reticulatus was evaluated by scanning electron microscope (SEM) examination of adult ticks, cross-breeding experiments and molecular biological analysis of eggs derived from transspecific pairings. The SEM investigations including the morphometric quantification of phenotypic features, resulted in an unequivocal differentiation of adultD. marginatus andD. reticulatus ticks. The cross-breeding experiments demonstrated that irrespective of whether female ticks of both species were applied with con- or transspecific male ticks or without males to sheep, they engorged and laid eggs. The larvae, however, developed only in eggs which originated from conspecific matings. A nested polymerase chain reaction (PCR) of the second internal transcribed spacer (ITS2) using the DNA of eggs from transspecific pairings and sequencing of the PCR products revealed two different genotypes. The genotypes of eggs originating fromD. marginatus andD. reticulatus females of these pairings differed. However, the eggs deposited byD. marginatus always possessed the same two genotypes as did the eggs produced byD. reticulatus. These results argue for a strict reproductive isolation ofD. marginatus andD. reticulatus and, therefore, for a separate species status.     

Comparative Prey Suitability ofOstrinia nubilalisEggs andAcyrthosiphon pisumforColeomegilla maculata

The effects ofOstrinia nubilalis(Hübner) (Lepidoptera: Pyralidae) eggs andAcyrthosiphon pisum(Harris) (Homoptera: Aphididae), when provided as single prey species and in combination, on life history characteristics ofColeomegilla maculataDeGeer (Coleoptera: Coccinellidae) larvae and adults were quantified. Preimaginal development was not influenced by the larval prey regime; development at 26 ± 1°C was completed in approximately 13.5 days onO. nubilaliseggs,A. pisum,orA. pisumalternated daily withO. nubilaliseggs. The resulting adults weighed 13.0, 10.7, and 12.5 mg when reared onO. nubilaliseggs,A. pisum,andA. pisumalternated daily withO. nubilaliseggs, respectively. Eighteen percent of the individuals died when reared onA. pisum,28% died when reared onO. nubilaliseggs, and 22% died when fedA. pisumalternated daily withO. nubilaliseggs. Seven adult diet combinations, based on diet regimes of larvae and adults, did not cause significant differences in preoviposition period, interoviposition period, and the number of days on which eggs were laid. Total fecundity was influenced both by larval and adult diet. The diet that resulted in highly fecund females wasA. pisumalternated daily withO. nubilaliseggs for larvae andO. nubilaliseggs for adults. FemaleC. maculatafedO. nubilaliseggs had the highest intrinsic rate of increase and net reproductive rate.     

Development of the cottid fish,Pseudoblennius percoides,reared in the laboratory,with brief descriptions of juvenileP. marmoratus andP. zonostigma

Embryonic, larval and juvenile development of the cottid fish,Pseudoblennius percoides were described on the basis of a series of laboratory-reared specimens. The eggs were demersal, adhesive, almost spherical in shape, measuring 1.66–1.82 mm in diameter, and with numerous various-sized oil globules. Neighboring eggs adhered to each other to form an egg mass. Hatching occurred between 13 and 16 days after spawning at a water temperature of 15.4 to I6.5°C. Newly hatched larvae measured from 6.5 to 7.3 mm, averaging 6.9 mm TL, and possessed 40 myomeres. Absorption of the yolk was completed at about 7.5 mm TL. Flexion of the notochord started and finished at about l0 mm TL and about 14 mm TL, respectively. Aggregate numbers of all fin rays were completed at over 16 mm TL, when the larvae reached the juvenile stage. The pigment pattern became the same as that of adults in juveniles longer than 25 mm TL. Lateral lines were completed at over 44 mm TL, when the juveniles attained to the young stage. The early stages of this species were clearly distinguished from those ofP. cottoides, and the juveniles of fourPseudoblennius species, i.e.P. percoides, P. cottoides, P. marmoratus andP. zonostigma, could be identified mainly by their pigment patterns.     

Interspecific competition among endoparasitoids of tobacco budworm larvae [Lep.: Noctuidae]

The ability of female larvae endoparasitoids [Microplitis croceipes Cresson:Cardiochiles nigriceps Viereck andCumpoletis sonorensis (Carlson)] to distinguish between unparasitized tobacco budworm,Heliothis virescens (F.), larvae andH. virescens larvae parasitized by the egg-larval parasitoidChelonus insularis,Cresson, was determined in laboratory studies. The 3 species of larval endoparasitoid females did not appear capable of distinguishing between unparasitized andC. insularis parasitized larvae resulting in multiple parasitoidism. The results of the ensuing competition between the 3 species for possession of the host demonstrated that bothC. sonorensis andM. croceipes were intrinsically superior toC. insularis. Both larva endoparasitoids destroyed the olderC. insularis larvae by physically attacking the latter. The presence ofC. insularis larvae in the host was found to prevent the hatch of compeatingC. nigriceps eggs through physiological suppression. The results show that the early attack of a host, as in the egg-larval parasitoid habit, is not necessarily advantageous.     

Influence of crucifer cropping system on the parasitism ofPlutella xylostella (Lep., Yponomeutidae) byCotesia plutellae (Hym., Braconidae) andDiadegma semiclausum (Hym., Ichneumonidae)

Field experiments were conducted to study the influence of cabbage monoculture and mixed cropping on the parasitism of diamondback moth,Plutella xylostella (L.), a destructive pest of all crucifers, by 2 larval parasites,Diadegma semiclausum Hellén andCotesia plutellae Kurdjumov. There was no significant difference in parasitism by either species whether cabbage was planted in insecticide-free monoculture or in mixed cropping with 8 noncrucifers which were sprayed twice a week with chemical insecticides mevinphos, methamidophos and permethrin. Population ofP. xylostella increased as the cabbage plants grew older. Parasitism byC. plutellae was higher soon after cabbage transplanting but decreased as the plants grew older. Parasitism byD. semiclausum was very low soon after cabbage planting but increased as the plants grew older. A significant negative correlation was found betwen parasitism byC. plutellae andD. semiclausum. In a caged field study where only one parasite species was used in an individual cage, parasitism ofP. xylostella by both species decreased as theP. xylostella population increased. This is believed to be due to the absence of competition between the two parasites inside the cage. There was no relationship between host-plant age and parasitism ofP. xylostella larvae by either parasite species.     

Regulation of host larval development by the egg-larval endoparasitoidChelonus insularis [Hym.: Braconidae]

In laboratory studies the effect of parasitism by the egg-larval endoparasitoidChelonus insularis Cresson on the resulting larvae of 2 host species,Heliothis virescens (F.) andSpodoptera ornithogalli Guénée) were determined by comparing daily measurements of larval weights. Growth of parasitized larvae of both host species was slower than growth of unparasitized larvae. Injections of fluids from the female parasitoid's calyx or poison gland intoH. virescens eggs retarded subsequent larval growth. However, a combination of fluids from these 2 organs produced the most significant reduction in the host larval growth rate. The growth reducing factor(s) was also effective when injected into 5-day-old host larvae.     

Experiments on inter-specific competition between three species of Tachinids attacking the sugar cane moth borer,Diatraea saccharalis (F.)

Three species of Tachinids (Lixophaga diatraeae T.T.,Paratheresia claripalpis van der Wulp, andMetagonistylum minense T.T.) were used to study intrinsic larval competition under laboratory conditions in Barbados. When equal numbers of freshly hatched larvae ofLixophaga andParatheresia were simultaneously inoculated into fullgrown moth borer caterpillars, both parasite species survived in equal proportions. In simultaneous inoculations ofMetagonistylum andLixophaga the first-mentioned species was clearly inferior (ratio about 1∶2). In inoculations withMetagonistylum andParatheresia the intrinsic inferiority of the first-mentioned species was still more pronounced (ratio 1∶5). When maggots of all three species were inoculated simultaneously the ratio of parasite survival forLixophaga: Paratheresia: Metagonistylum was approximately 2∶2∶1, indicating again thatMetagonistylum is the inferior species, whereasLixophaga andParatheresia are equally competitive. The results described above did not change appreciably when one species was given a numerical advantage over the other, e.g. when three maggots ofMetagonistylum were simultaneously inoculated with only one maggot ofLixophaga (orParatheresia). In most of these tests,Lixophaga andParatheresia still remained the superior species. When maggots of one species were inoculated two days in advance of the other species — i.e. when one species had a developmental advantage — the earlier inoculated species usually survived in greater proportions than it would have in simultaneous inoculations. Under Barbados conditions the larval period ofLixophaga is the shorter (5 days), followed byMetagonistylum (6–7 days), and the longest larval period occurs inPara heresia (7–9 days). When a species with a faster development was inoculated two days in advance of a species with a slower development (e.g.Lixophaga two days in advance ofParatheresia), the developmental difference between the two species was magnified and the earlier inoculated species was then clearly the superior one. When, on the other hand, a species with slower development was given a two-day advantage in time the slower growing species survived in greater proportions than it would have done in simultaneous inoculations. The developmental advantage of its competitor was, in this case, eliminated.     

Host habitat finding and host selection of theDrosophila parasitoidLeptopilina australis (Hymenoptera,Eucoilidae), with a comparison of the niches of EuropeanLeptopilina species

Summary Decaying petioles of giant hogweed,Heracleum mantegazzianum Sommier & Levier, are used as a breeding site by six species ofDrosophila and the drosophilidScaptomyza pallida. The most numerous parasitoid species associated with this community isLeptopilina australis. BecauseL. australis was previously unknown in western Europe, we present the characters to distinguish it form its close relativeL. clavipes. Experiments on host species selection and survival ofL. australis showed that this parasitoid mainly usesD. limbata as host. Olfactometer experiments showed thatL. australis is attracted by the odour of decaying hogweed stalks, especially when these contain larvae ofD. limbata. L. australis is also strongly attracted by the odour of stinkhorns, a habitat in which it has never been found in nature.D. phalerata is the dominant fly species in stinkhorns, and is not a host ofL. australis. We offer a possible functional explanation for this unexpected habitat choice, by showing thatD. transversa andD. kuntzei, both species found to breed in fungi, are also suitable hosts forL. australis. We also discuss habitat choice with regard to a proposed phylogeny of theLeptopilina species in temperate Europe. Finally, we discuss niche overlap ofL. australis with the otherLeptopilina species.     

Cannibalism and interspecific predation in two predatory ladybirds in relation to prey abundance in the field

Life tables for two predatory ladybirds,Coccinella septempunctata andHarmonia axyridis, were constructed in two years in which prey abundance differed. The prey aphid,Aphis gossypii, was abundant on its primary host from late May to late June. Females ofH. axyridis andC. septempumctata laid their eggs during the increase and peak in aphid abundance. The oviposition period ofC. septempunctata started before and was shorter than that ofH. axyridis. In both species, intraguild predation and/or cannibalism of the egg and fourth instar stages, but rarely of other developmental stages, were observed. Fourth instar larvae ofH. axyridis had to complete their development when aphids were scarce more frequently than those ofC. septempunctata. The highest frequency of intra- and interspecific predation was of fourth instarH. axyridis larvae. In terms of intraguild predation, the larvae ofH. axyridis preyed on larvae ofC. septempunctata, but the reverse was not observed. Percentage survival from egg to adult inH. axyridis was higher than inC. septempunctata in both years, and least in both species in the year of low aphid abundance. These results suggest that prey abundance influenced the frequency of cannibalism and intraguild predation, which were important in structuring this guild of ladybirds.     

Relations between water mites of the genusHydrachna and the corixidsSigara striata andCymatia coleoptrata

The larvae of the water mitesHydrachna conjecta andH. cruenta are parasitic on corixids.H. conjecta larvae are attached to the underside of the hemelytra of the host and those ofH. cruenta to the legs. The growth ofH. cruenta larvae is less than that of the more shelteredH. conjecta larvae. The infection influences the egg production of the host: infectedSigara striata females have fewer eggs in the ovarioles than uninfected ones. The number of eggs in the ovarioles of the host is related to the size of the parasite. It may be assumed that the presence ofH. conjecta larvae causes a lower fecundity in the host than those ofH. cruenta. InCymatia coleoptrata, a much smaller host thanS. striata, the fecundity is even more impaired by both parasite species. For in the ovarioles of infectedC. coleoptrata females no developed eggs were found at all. So, it is clear that it is anyhow the relation between body size of host and parasite that matters.