Extra-oral digestion and the problem of parasitism in Parasitengona mites (Acariformes)

An analysis of the extra-oral digestion in Parasitengona being a highly specialized group of Acariform mites is carried out from the viewpoint of functional morphology and ecology. The significance of the extra-oral digestion in the life strategy of these mites and their larval parasitism is also evaluated. The morphological pre-adaptations of this mode of feeding as well as its probable evolutionary consequences are demonstrated by an example of trombiculid mites (Trombiculidae). It is shown, in particular, that parasitism in general may be considered as a particular life scenario implying that the feeding preferences of the organism are evolutionary formed in a close association with other organisms, which provide a parasite with a feeding substrate mainly already prepared for utilization. Based on this assumption, all Parasitengona, including both larval and post-larval instars, irrespectively of the size of their potential victim, preferably should not be considered as parasites, but as micro-predators.     

The origin of parasitism in trombiculid mites (Acariformes: Trombiculidae)]

On the basis of literary data and original investigations some phylogenetic, ecological and morphological aspects of the origin of parasitism in trombiculid mites are carefully considered for the first time. It is shown that parasitism in this group of trombidiform mites is a relatively young historical phenomenon and was formed after their ontogenesis had differentiated into active and quiescent stages. Therefore, in the life pattern of trombiculid mites the character of individual development, that defines their biotopical restriction, is much more important than the phase parasitism. Primitive organization of the digestive system and extraintestinal digestion, so characteristic of this group, are one of the main reasons of the origin of their parasitism. Under pasture conditions trombiculid mites, that initially were predators-entomophages with bite-sucking mouth parts, pass easily to parasitism on vertebrate animals and become primary lymphophages. They use the vertebrate host's organism exclusively as a source of food and by the extent of polyphagia are very close to free-living blood-sucking insects. Stylostome, that develops during feeding of trombiculid larvae and some other closely related groups of trombidiform mites, is a universal structure for achieving a large amount of food on a wide range of animals during a relatively short period of time and reflects wide host-parasite specificity of these parasitic mites. From the historical view the larvae of trombiculid mites did not pass from one group of hosts to the others, but owing to morphological preadaptation to parasitism passed in a definite historical period, not earlier than Paleogene, to parasitism on all classes of terrestrial vertebrates, especially on mammals, their primary hosts.     

Study on vector mites of tsutsugamushi disease in Cheju Island, Korea.

Because no reference on trombiculid mites (Acarina: Trombiculidae) in Cheju Island where tsutsugamushi disease is highly endemic had been available, studies on trombiculid mites in Cheju Island were implemented during the period of August 1991-April 1992, and the results obtained are summarized as follows: (1) The species and numbers of the field rodents collected were 143 Apodemus agrarius chejuensis (92.3%), 11 Crocidura lasiura (7.1%) and 1 Micromys minutus (0.6%). From total 12,075 chiggers harvested, 9 species of 4 genera in Trombiculidae were identified. (2) The predominant species through all seasons was L. zetum (43.3%), followed by L. orientale (27.4%) and L. scutellare (26.6%). However, in autumn when the most cases of tsutsugamushi disease occur, L. scutellare was prominently predominant, having 79.8% of the collected chiggers. (3) Among 1,142 L. scutellare examined for Rickettsia tsutsugamushi by means of IFA test, 6 individuals were found positive showing 0.5% of infection rate. This is the first finding that L. scutellare is the second vector species of tsutsugamushi disease in Korea. (4) Antibody positive rate of A. agrarius chejuensis sera were 31.2% (44/139), and 1 M. minutus serum was also found positive. The seropositive rates by season were not so significantly different.     

恙螨杂交的研究

本文报道了在实验室内对微红纤恙螨和地里纤恙螨进行杂交试验,再次征明这两种恙螨不容易杂交,偶然条交后其繁殖率与成活率比纯种配对的低得多.从F₁繁殖至F₂更困难,而且F₂的成活率更低,说明两者有生殖隔离现象.杂交子代的背板测量数据和幼虫体色出现中间类型,少数个体出现畸形和背毛变异等.以上异常现象在实验室纯种繁殖多代中极少见到.这一切为研究恙螨的种型和正确对待庞大的纤恙螨亚属中幼虫的分类具有重要意义.     

Life cycle and parasitic interaction of the lizard-parasitizing mite Ophionyssus galloticolus (Acari: Gamasida: Macronyssidae), with remarks about the evolutionary consequences of parasitism in mites

Wild-caught specimens of the lacertid lizard Gallotia galloti eisentrauti from the Canary Island of Tenerife were checked for ectoparasites. The parasitic gamasid mite Ophionyssus galloticolus Fain and Bannert (2000) was very abundant on these lizards. Additionally, parasitism by larvae of two species of Trombiculidae (Prostigmata: Parasitengona) was observed. O. galloticolus was reared in the laboratory on its natural host in order to investigate its life cycle, reproductive biology, and development. The life history of O. galloticolus is documented in detail and compared to literature data of other Ophionyssus species. O. galloticolus was found to be similar to other species of the same genus with respect to the duration of development, the precopulatory association of protonymphs, and the arrhenotokous development of eggs. However, it seems to be more tolerant towards low relative humidity and longer starvation periods than other Ophionyssus species. Evolutionary transformations of the life-history pattern of this genus and other parasitic mites in comparison to its predatory precursors involve a reduction or partial suppression of ontogenetic instars in order to decrease mortality during host-seeking phases, and a compensating increase in growth capacity of the remaining feeding instars facilitated by replacement of sclerites through elastic cuticle or by growth of new cuticle unrelated to a moult (neosomy).     

Ultrastructure of the integument during moulting of the quiescent tritonymphal instar of trombiculid mite Hirsutiella zachvatkini (Acariformes: Trombiculidae)

The ultrastructure of the integument of the quiescent reduced tritonymph of the trombiculid mite Hirsutiella zachvatkini (Schluger) was investigated by means of transmission electron microscopy. Mites were investigated daily during the 14–16 day tritonymphal period (imagochrysalis). This period includes the deutonymphal moult (1–3 days), the quiescent tritonymph period (2–4 days), and the tritonymphal moult into the adult mite (6–10 days). A distinct recognizable feature of the tritonymphal moulting cycle is a sequence of events independent of precise time intervals. This process involves partial destruction and reorganization of the hypodermis of the previous instar, and formation of a new hypodermis of the subsequent instar from islands of rudimentary hypodermal cells. The integument of the reduced tritonymph differs greatly from that of both larva and active deutonymph and adult. It consists of a simply organized hypodermal layer of varying thickness and a thick clear poorly lamellate cuticle with curved pore canals, and lacking setae. The epicuticle is very thin and without a clear protein layer. The tritonymphal instar as such with its own cuticle situated near the hypodermis is encased within the detached covering of the previous active deutonymph, and may be considered a calyptostasic and entirely pharate instar. There is a tendency for reduced tritonymphal stage to be eliminated from ontogenesis and this stage is not homologous to the pupa of insects.     

Changes in cell type composition and enzymatic activities in the hepatopancreas of<Emphasis Type="Italic"> Marsupenaeus japonicus</Emphasis> during the moulting cycle

The goal of the present study was to evaluate the changes in the cell type composition and ATPase activities (total ATPase, ouabain-sensitive Na+/K(+)-ATPase, furosemide-sensitive Na(+)-ATPase) that occur during the different stages of the moulting cycle in the hepatopancreas of the Marsupenaeus japonicus. The results clearly suggest that the number of resorptive and fibrillar cell types changes significantly during the different stages. An inverse correlation between resorptive and fibrillar cells is observed during moulting (both in normally fed and fasted animals). Fasting, but not the moulting cycle, affects the number of blister-like cells. In the resorptive cells the enzymatic activities (total ATPases and ouabain-sensitive Na+/K(+)-ATPase) also change during the moulting in a cyclical manner. All these results are in agreement with and confirm the different functions carried out by the two cell types within the hepatopancreas.     

Evidence for co-invasion events: different chigger species (Actinotrichida,Trombidioidea: trombiculidae) share a host

Cases of co-invasion of various chigger species parasitizing murids and cricetids in various habitats were analysed using morphological and molecular approaches. Here we provide evidence for 25 new cases of co-parasitism of chigger mites on rodent hosts (Myodes glareolus, Apodemus flavicollis, Apodemus agrarius) accounting for 8.6% of all host-parasite associations observed in this study. The results confirm higher incidence of co-parasitism in vertebrate-associated Parasitengona mites compared to arthropod-associated ones. Among factors influencing the occurrence of co-parasitism in Trombiculidae the body constitution and year-round availability of hosts associated with lower host specificity of larvae should be considered.     

Influence of azadirachtin on development and reproduction of Nezara viridula L. (Het., Pentatomidae)

Abstract:  The potential of azadirachtin as an insect growth regulator was evaluated in Nezara viridula L. by applying different doses to fifth instar nymphs. At doses of 200–500 ng per insect almost all the individuals died during moulting to adults and the survivors showed a great number of nymphal characteristics, and also died very soon after. At lower doses, from 2 to 50 ng per insect, approximately 50% of the adults seemed normal. No effect was observed during the last nymphal instar, even at the highest dose applied. The fertility and fecundity of adults, males and females, developing from nymphs treated with different low doses of azadirachtin were also studied. When azadirachtin was applied at 20 ng per insect on fifth instar nymphs, females developing from these nymphs showed a conspicuous reduction of fecundity. This same effect was evident when untreated females mated with males obtained from treated nymphs. Finally, azadirachtin applied at 1  μ g/cm² to the oviposition surface showed a remarkable oviposition repellency.     

Moulting of mechanoreceptive hair sensilla of Lepisma saccharina (Zygentoma) and Machilis spec. (Archaeognatha)

In all insects investigated hitherto the mechanoreceptive hair sensilla possess the same organization plan. There are differences in the moulting process of hemimetabolous insects. While the functions of the three enveloping cells are corresponding, the position of the moulting porus is different. In Gryllus and Periplaneta the moulting porus is situated at the base of the hair, in Machilis 25 mum above the base of the hair. In Lepisma, however, the moulting porus is located at the tip of the hair shaft. Comparison of mechanoand contactchemoreceptive hair sensilla shows that the position of the moulting porus in primitive ectognathous insects represents an argument for the close morphological and phylogenetical relationship between both types of sensilla. Interpreting our results, the original position of the moulting porus is at the tip of the hair sensilla. In mechanoreceptors, where the moulting porus is located at the base of the hair, the original tip of the hair (position of the moulting porus) is overgrown at the side by a 'secondary hair process'.     

MOULTING RHYTHM IN THE ALIENICOLAE OF APHIS FABAE SCOP. (HEMIPTERA: APHIDIDAE) IN THE FIELD

In a natural population of alienicolae of Aphis fabae Scop, on field beans in July 1952, the frequency of moulting of the last larval instar into the alate form was usually relatively high between about 04.00 and 08.00 hr. G. M. T. This high rate was followed by a decline to a lower fluctuating rate for the rest of the day. The moulting rate at night was usually very low.
The high rate of moulting in the morning, just as the temperature is rising, may be due to acceleration of nymphal development which leads to a synchronization of moulting, much as teneral development of alatae, if accelerated, produces flight peaks during the day (Johnson, Taylor & Haine 1957): data on the relations of moulting and nymphal development to temperature are, however, insufficient for making a complete analysis along these lines.
Changes in moulting rate during the rest of the day are correlated with temperature and with time, both independently. A rise of 1°C. ambient temperature is associated with an 11.6% rise in moulting rate: a fall of 1°C. with a drop of 10.5% and a lapse of 1 hr. in time by a 5.4% drop in the rate. Sunshine and humidity show no simple correlation with moulting rate.     

The overwintering stages of Ectobius lapponicus (L.) (Dictyoptera: Blattidae)

An account is given of the overwintering stages of Ectobius lapponicus, involving the determination of a diapause in the egg and one of the nymphal instars. The significance of these periods in the life cycle is discussed.     

Functions of the ecdysone receptor isoform-A in the hemimetabolous insect Blattella germanica revealed by systemic RNAi in vivo

The molecular basis of ecdysteroid function during development has been analyzed in detail in holometabolous insects, especially in Drosophila melanogaster, but rarely in hemimetabolous. Using the hemimetabolous species Blattella germanica (German cockroach) as model, we show that the ecdysone receptor isoform-A (BgEcR-A) mRNA is present throughout the penultimate and last nymphal instars in all tissues analyzed (prothoracic gland, epidermis and fat body). To study the functions of BgEcR-A, we reduced its expression using systemic RNAi in vivo, and we obtained knockdown specimens. Examination of these specimens indicated that BgEcR-A during the last nymphal instar is required for nymphal survival, and that reduced expression is associated with molting defects, lower circulating ecdysteroid levels and defects in cell proliferation in the follicular epithelium. Some BgEcR-A knockdown nymphs survive to the adult stage. The features of these specimens indicate that BgEcR-A is required for adult-specific developmental processes, such as wing development, prothoracic gland degeneration and normal choriogenesis.     

Histones of spermatogenous cells in the house cricket

Histones were isolated from testis of the house cricket and analyzed by electrophoresis on polyacrylamide gels containing urea and acetic acid. Testes of two different nymphal instars and of adults were examined. The testes contained gonial and meiotic stages in the younger nymphs analyzed, and these same stages plus early spermatids in the older nymphs. At both nymphal instars, testis histone displayed the same five major fractions that are found in somatic nuclei of the cricket; the only unusual feature noted in nymph testis was a high abundance of phosphorylated F1. Adult testis has the same histone fractions as nymph testis and has two new fractions in addition. SDS electrophoresis also shows the presence of two more histones in adult testis than in nymph testis. — The unusual testis histones appear to accumulate during the nuclear elongation stages of spermiogenesis. The occurrence of these stages in adult testis is correlated with the presence of the extra histones. Nuclei of adult testis were separated into fractions enriched for early, mid, and late stages by velocity sedimentation at unit gravity. The unusual histones predominate in the fractions enriched for late spermiogenic stages. Both of the new histones appear to occur in the same stages of spermiogenesis, and display linked accumulation. Eventually they make up at least seventy percent of the histone complement.     

Multiple Environmental Factor Analysis in Habitats of the Harvest Mite Neotrombicula autumnalis (Acari: Trombiculidae) Suggests Extraordinarily High Euryoecious Biology

The harvest mite Neotrombicula autumnalis (Trombiculidae) has become a great nuisance in various vegetated areas in Germany over the last 15 years. According to reports of dermatologists, this species appears to have propagated and spread significantly. Moreover, cases of severe trombidiosis or trombidiosis-like skin reactions have been noticed at unusually early times of the year. Due to the lack of scientific studies, little is known about the ecology of N. autumnalis and its distribution, and preferred habitats cannot be predicted. A four-year study was conducted to identify trombiculid foci in different areas of Bonn in order (1) to determine the timing of larvae appearance in different years, (2) to identify the factors that lead to high larvae abundances at the mite foci (‘multiple factor analysis’), and (3) to develop an ecological control strategy. By means of the ‘tile catch method’ (TCM) which turned out to be most appropriate to collect data on the distribution and abundances of trombiculid mites, larvae of N. autumnalis were caught from mid July until the end of October/beginning of November. The distribution of the mites was patchy, supporting the hypothesis that certain factors cause a concentration in foci. Most of the mite foci had a fixed location for at least three years. Efforts to isolate nymphs and adults in larger quantities to gain knowledge about their preferred soil areas and soil depths failed. Only some nymphs of N. autumnalis could be found living 10–40 cm deep in the soil. Due to the restriction that the nymphs and adults can only rarely be isolated in the ground, the analysis of environmental factors was executed based on abundances of questing larvae on the soil surface. The detailed analysis of soil-physical, soil-chemical and meso-faunistic factors could not finally explain the unequal distribution of the mites, although the porosity of the soil had a statistically significant slight influence on the abundance of larvae, and soil pH bordered significance, also suggesting a slight influence. Furthermore, soil temperatures during the winter seasons in three subsequent years appeared too high to affect the harvest mite. The field experiments suggest that N. autumnalis and particularly its larval stages are extremely euryoecious (meaning tolerating very different environmental conditions). Further studies are necessary: additional investigations on the influence of certain abiotic environmental factors on N. autumnalis, the search for factors underlying the rhythmicity of its life cycle (‘zeitgeber’), and the reasons and mechanisms for heterogeneous distribution of soil fauna in general. Ecological control of the mite is, in principle, possible but only after identifying the foci and ascertaining their approximate dimensions with the TCM. This control strategy is the most promising one, albeit very laborious, emphasising the need of further research on the ecology of the harvest mite.     

Developmental strategies in Ectobius pallidus (Dictyoptera: Blattidae)

Ectobius pallidus has a semivoltine life cycle, overwintering as an egg and intermediate nymphal instar. A range of instars may overwinter, although the exact composition of an overwintering population varies annually. A number of developmental pathways are defined, involving both quiescence and diapause. The proportion of an instar following each pathway also varies annually. In ‘advanced’ years more 3rd and 4th instars enter diapause. The ecological significance of the different developmental strategies is discussed.     

Comparative studies on alate wing formation in two related species of rotten-wood termites: <Emphasis Type="Italic">Hodotermopsis sjostedti</Emphasis> and <Emphasis Type="Italic">Zootermopsis nevadensis</Emphasis> (Isoptera,Termopsidae)

Summary Termite colonies are comprised of several types of castes that differentiate throughout postembryonic development. In termopsid termites (family Termopsidae), alates are normally differentiated from apterous instars by two nymphal instar stages and three moulting events. Here, we report that of the rotten-wood termite Hodotermopsis sjostedti. There is only a single nymphal instar between the pseudergate and alate stages. During the annual alate production season in June/July, we observed some nymphs with small wing buds which were dorsally swollen. Those nymphal individuals subsequently moulted into alates through only a single moult. We examined their histology and internal morphology and observed that the folding pattern of the newly formed wings was very different from that seen in second stage nymphs of the closely related species Zootermopsis nevadensis. The newly formed wings of H. sjostedti are formed inside the relatively smaller wing buds and therefore must be folded in a complicated manner. Our observations revealed that the tips of the folded wings were elongated and bent, such that they overlapped in the median plane. We suggest that heterochronic evolutionary change accounts for the compression of nymphal development into a single instar. We also suggest that this probably occurred at either the individual or colony level in this species.Received 18 August 2003; revised 11 December 2003; accepted 8 January 2004.     

Identification of potential hosts and vectors of scrub typhus and tick-borne spotted fever group rickettsiae in eastern Taiwan

Scrub typhus and tick-borne spotted fever group (SFG) rickettsioses are transmitted by chiggers (larval trombiculid mites) and hard ticks, respectively. We assessed exposure to these disease vectors by extensively sampling both chiggers and ticks and their small mammal hosts in eastern Taiwan during 2007 and 2008. The striped field mouse Apodemus agrarius Pallas (Rodentia: Muridae) was the most common of the small mammals (36.1% of 1393 captures) and presented the highest rate of infestation with both chiggers (47.8% of 110 760) and ticks (78.1% of 1431). Leptotrombidium imphalum Vercammen-Grandjean & Langston (Trombidiformes: Trombiculidae) and immature Rhipicephalus haemaphysaloides Supino (Ixodida: Ixodidae) were the most abundant chiggers (84.5%) and ticks (>99%) identified, respectively. Immunofluorescent antibody assay revealed high seropositive rates of rodents against Orientia tsutsugamushi Hyashi (Rickettsiales: Rickettsiaceae), the aetiological agent of scrub typhus (70.0% of 437 rodents), and tick-borne SFG rickettsiae (91.9% of 418 rodents). The current study represents a first step towards elucidating the potential hosts and vectors in the enzootic transmission of O. tsutsugamushi and tick-borne SFG rickettsiae in Taiwan. Further studies should focus on characterizing pathogens in L. imphalum and R. haemaphysaloides, as well as the proclivity of both vectors to humans. Uncovering the main hosts of adult ticks is also critical for the prevention of SFG rickettsial infections.     

Multiplex PCR assay for identifying five species of chigger mites in the Republic of Korea

Chigger mites (Trombiculidae), which are known vectors of Orientia tsutsugamushi, have significantly fewer molecular data available than other known species, with a focus on morphological species identification rather than molecular species identification. However, chigger mites are easily damaged because of small size. In addition, natural variation and adult similarity would interrupt accurate classification and identification. Therefore, in this study, a multiple polymerase chain reaction (PCR) method using the internal transcribed spacer (ITS) region of five frequently occurring species (Euschoengastia koreaensis, Leptotrombidium orientale, Leptotrombidium pallidum, Leptotrombidium palpale, and Leptotrombidium scutellare) among eight species known to mediate the spread of is presented. This is the first report using molecular species identification for the classification method of chigger mites, which was only possible with morphological species identification, and is expected to be used as basic data for vector surveillance.