Geographic variation of diapause intensity in the spider mite Tetranychus urticae

Abstract. Eight strains of the spider mite Tetranychus urticae, originating from different localities in western and central Europe, with latitudes ranging from 40.5 to 60^oN, displayed marked differences in the period of chilling at 4^oC required for diapause termination under a diapause-maintaining short-day photoperiodic regime at 19^oC, to which the mites were transferred after the cold period. The higher the latitude from which the strains originated the longer was the period of chilling required for diapause termination, suggesting the presence of a gradient in diapause intensity, diapause being deeper the more northern the origin of the strains. Two strains originating from higher altitudes appeared to have a much deeper diapause than expected from their latitudinal origin. In addition, these two mountain strains showed mutual differences in diapause intensity, notwithstanding the fact that they originated from similar latitudes and altitudes; local climatic conditions probably act as strong selective forces with regard to diapause depth. All strains appeared to be sensitive to photoperiod during the period of diapause development. Diapause was quickly completed by a long-day photoperiod (LD 17:7 h), but was maintained by a short-day photoperiod (LD 10:14h). However, even under the latter regime sensitivity to photoperiod gradually diminished and eventually disappeared, thus leading to ‘spontaneous’ termination of diapause. The length of the period of diapause development, as measured by the sensitivity to photoperiod of diapausing mites, varied between strains; it was shorter in the southern strains and longer in the northern strains. The results indicate great variation in diapause intensity between strains, which is probably genetically determined and may have adaptive significance for this widespread species. When young females which had just entered diapause were kept for ever longer periods of time under the diapause inducing short-day regime at which they had been reared, before being transferred to the cold room, the duration of the period of chilling required for diapause termination was found to decrease proportionally in all three strains tested. These results suggest that intensification of diapause does not occur in T. urticae; diapause intensity seems to be highest at the beginning of diapause and to diminish gradually during diapause development.     

Walking,feeding and intraspecific interaction of larvae of Metaseiulus occidentalis,Typhlodromus pyri,Neoseiulus fallacis and Amblyseius andersoni held with and without eggs of Tetranychus urticae

Larvae of Metaseiulus occidentalis (Nesbitt), Typhlodromus pyri Scheuten, Neoseiulus fallacis (Garman) and Amblyseius andersoni Chant exhibited different activity levels when held on apple leaf or on tile arenas and given or not given eggs of Tetranychus urticae Koch and water (tiles only). M. occidentalis larvae held without prey exhibited high levels of walking (includes searching) during 24 hours of evaluation, whereas M. occidentalis larvae held with prey fed quickly and then became less active. Fed larvae of M. occidentalis were less active on leaves than tile. Larvae of T. pyri on leaves had a very low frequency of walking, almost never fed and quickly assumed a resting position during development. While much less active than M. occidentalis, fed and unfed T. pyri larvae walked more on tiles than leaves before resting. Larvae of N. fallacis and A. andersoni fed at low rates and were similarly active on tiles and leaves. Free water increased walking by M. occidentalis, A. andersoni and T. pyri on tile but not N. fallacis. M. occidentalis larvae interacted 5–7 times more often than larvae of the other three species. Cannibalism or scavenging was rarely seen and then only for M. occidentalis larvae. Larvae of all four mites walked, fed and interacted much more in the first 12 hours than the second 12 hours of tests, except unfed M. occidentalis. Unfed M. occidentalis larvae did not molt to protonymphs but unfed larvae of the other three species did. Unfed and fed protonymphs of all four species walked more at 4 hours after molting than larvae at 12–24 hours. Unfed and fed protonymphs of T. pyri or A. andersoni had similar walking frequencies, but unfed protonymphs of N. fallacis were more active than fed ones. Trends in larval activities are discussed relative to the life history of each species.     

Cascading tripartite binomial classification plans to monitor European red mite (Acari,Tetranychidae) through a season; development and evaluation of a new methodology for pest monitoring

A monitoring protocol that schedules future sample bouts based on the outcome of density classification and expected population growth has been developed and applied to monitoring European red mite (Panonychus ulmi Koch) through a growing season. The monitoring protocol is based on concatenating through time tripartite sequential classification sampling plans that use binomial counts in lieu of complete enumeration. Binomial counts are scored positive when the number of organisms (mites) on a sample unit (leaves) exceeds a tally number. At each sample occasion the monitoring procedure leads to one of three possible decisions; intervene when the density is high, sample at the next sample occasion (after one week) when the density is intermediate, and sample at the second next sample occasion (after two weeks) when the density is low. Evaluation of the monitoring protocol under field conditions showed that the protocol with constituent tally 0 binomial count sampling plans was quite successful in timing intervention at the moment when population densities were about to exceed an established threshold that dictated intervention. The performance of this monitoring protocol and another protocol in which constituent sampling plans used binomial counts with a tally number of 4 were compared using simulation. Sampling plans that used a tally number of 4 were more precise than plans that used a tally number of 0. However, the overall performance of the monitoring protocol based on tally 0 sampling plans did not greatly differ from the monitoring protocol based on tally 4 sampling plans. Simulated performance of the tally 0 protocol was corroborated by field evaluation. The monitoring protocol based on tripartite classification required 30 to 45 percent fewer sample bouts than a protocol based on conventional sequential classification at weekly intervals. The monitoring protocol based on tripartite classification was also better able to schedule intervention when needed compared to a protocol based on conventional classification at two week intervals. Using the tally 0 protocol and current thresholds forP. ulmi, cumulative mite density was kept below 300 mite-days per leaf, which is well below levels regarded damaging. A tally 0 protocol with raised thresholds, developed on the basis of this finding, gave the best simulated performance of all protocols evaluated.     

The role of the sensitization to storage mites in the diagnosis of allergic respiratory diseases

Summary Numerous studies suggest the capacity of storage mites (S.M.) to induce IgE-mediated reactions but their etiopathogenetic role in allergic respiratory diseases has not yet been established. Therefore we examined 283 patients affected by rhinitis and/or bronchial asthma resident in urban and rural areas who underwent skin tests and a RAST with a group of allergens including S.M. (Acarus s., Lepidoglyphus d., Glycyphagus d., Tyrophagus p.).The incidence of patients showing a positive reaction to S.M. was evaluated according to their place of residence and work. 48 patients were selected who resulted positive to mites; 28 of them resulted positive to S.M. and pyroglyphid and 5 to S.M. only.The relationship between skin tests and RAST for S.M. positive patients resulted high forL.d. (70%),G.d. (75%),T.p. (80%) and low forA.s. (58%). In RAST positive subjects cross-reactivity withD. ptero was evaluated:A.s. (70%),L.d. (80%),T.p. (75.4%),G.d. (78.9%).Dwelling and place of work of skin and RAST positive patients revealed an equal distribution between urban and rural populations for S.M.; however, while in urban areas the association with pyroglyphid mites is constant, the rare single sensitivities are found only in rural areas and in farmers. From our data it emerges that the allergological diagnostics must use S.M. when considering respiratory diseases of professionally exposed subjects and residents of given areas. An interpretation of their etiologic role, given the frequent association with pyroglyphid mites, will demand further diagnostic data and an identification and purification of the clinically relevant allergens.     

Mating and spermatophore morphology of water mites (Acari: Parasitengona)

In this paper I synthesize original and published studies of sperm transfer behaviour of 23 genera of water mites from 15 families. The morphology of spermatophores from 16 genera (12 families) is described. Behaviour and/or spermatophores are described for the first time for the following species: Hydrachna magniscutata Marshall, Hydrachna hesperia Lundblad, Hydrachna sp. nr. leegei Koenike, Limnochares americana Lundblad, Limnesia undulata (Müller), Neumania distincta Marshall, Unionicola (three species in the U. crassipes-complex), Thyas slolli Koenike, Lebertia annae Habeeb, Lebertia sp., Piona sp. nr. debilis (Wolcott), Tiphys vernalis (Habeeb), Arrenurus dentipetiolatus Marshall, Arrenurus marshalli Piersig and Arrenurus birgei Marshall. On the basis of proximity of male and female during sperm transfer, I divide water mites into four groups: complete dissociation, involving no physical or chemical contact between the sexes (nine genera); incomplete dissociation, requiring distance-or contact-chemoreception but not involving pairing behaviour (five genera); pairing with indirect transfer, involving pairing behaviour with females controlling sperm uptake (three genera); pairing with direct transfer (=copulation), involving pairing behaviour and male placement of sperm in the receiving structure of the female (12 genera). Four genera have representative species in more than one category of sperm transfer. Factors possibly leading to the diversity of water mite mating behaviour include an evolutionarily flexible mode of sperm transfer in the ancestral water mite, and the development of planktonic and endoparasitic habits in many mites. Morphological features of spermatophores that improve physical stability, probability of females taking up sperm and resistance against osmotic stress are discussed. Finally, I present implications of mating behaviour and spermatophore morphology for phylogenetic relationships within water mites and between this group and terrestrial Acari.     

巴氏新小绥螨对同一栖息地枸杞瘿螨的捕食功能反应

枸杞瘿螨Aceria pallida Keifer（Acari: Eriophyoidae）是枸杞上为害最严重的有害生物之一。近期在内蒙古地区发现植绥螨巴氏新小绥螨Neoseiulus barkeri Hughes（Acari: Phytoseiidae）与枸杞瘿螨可同时发生在野生枸杞上。为评价巴氏新小绥螨对枸杞瘿螨的捕食潜力,本研究在室内25±1℃、RH 65%±10%、16 L∶8 D的条件下,研究了巴氏新小绥螨对不同密度枸杞瘿螨成螨（30、50、70、90、110、130、150、170头）的捕食功能反应及搜寻效应。结果表明,巴氏新小绥螨的雌、雄成螨对枸杞瘿螨成螨的捕食功能反应均为Holling-II型,即巴氏新小绥螨雌、雄成螨的捕食量随着猎物密度的增加而增加,一直到猎物密度较高时趋于稳定;而巴氏新小绥螨雌、雄成螨的搜寻效应随着猎物密度的增加而降低。巴氏新小绥螨雌成螨对相同密度下的枸杞瘿螨成螨的捕食量均高于雄成螨,而且雌成螨的搜寻效应也强于雄成螨。巴氏新小绥螨雌成螨的攻击率（α=4.4121）高于雄成螨（α=2.4403）,而雌成螨的处理时间（Th =0.0094 d）短于雄成螨（Th=0.0196 d）;雌、雄成螨的理论最大日捕食量（T/Th）分别为106.61头和51.02头。研究结果显示巴氏新小绥螨对枸杞瘿螨有较好的捕食潜力,性别对巴氏新小绥螨捕食枸杞瘿螨的功能反应有显著影响。     

Population- and ecosystem-level effects of predation on microbial-feeding nematodes

We studied the role of nematode predation in the functioning of detrital food webs assembled in microcosms. The microcosms contained defaunated humus and litter materials, a diverse microbial community with bacteria, fungi and protozoa, and a birch (Betula pendula) seedling infected with mycorrhizal fungi. Different levels of top-down control upon microbivorous nematodes were set up by assembling food webs either without predators, or in combinations with a specialist and a non-specialist predatory mite (Mesostigmata). The nematode community was composed of either (1) three species of bacterivorous, or (2) three species of fungivorous nematodes or (3) both groups together. After two growing periods for the birch (38 weeks), the microcosms were destructively sampled for animal and microbial biomasses, concentration of mineral N in the soil, plant biomass and plant N concentration. The specialist predator reduced biomasses of both bacterial- and fungal-feeding nematodes by more than 50%, whereas the non-specialist predator weakly increased the biomass of fungivorous nematodes. Thus, under high predation pressure, the biomass of microbivores changed as predicted by trophic dynamic models assuming strong top-down control and uniformly behaving trophic levels. Despite this, microbial biomass was unaffected by the predators. However, microbial respiration increased slightly in the presence of predators. Assuming that microbial respiration correlates with microbial productivity, the increase in microbial respiration indicates a cascading productivity regulation. The composition of the microbivore community had only a minor effect on the outcome of the top-down control on microbes. The >50% reduction in nematode biomass and respiration coincided with <16% increase in microbial respiration and did not affect microbial biomass. Presence of the specialist predator slightly reduced soil NH⁺ ₄ concentration in communities with fungivore nematodes but plant growth and N uptake remained unchanged. Thus, the structure of the community only weakly controlled nutrient mineralisation. Received: 18 May 1998 / Accepted: 3 May 1999     

江西蚌螨属七种记述(蜱螨亚纲:蚌螨科)

报道作者近几年采自江西的蚌螨属７种水螨,包括一新种：螯爪蚌螨,中国三新记录种：弯弓蚌螨,刺蚌螨,今村蚌螨,１９７８,三已知种;Ｙ纹蚌螨,台湾蚌螨,厚蚌螨,并对已知种作了必要描述。     

Competitive Exclusion,Harem Behaviour and Host Specificity of the Water Mite Unionicola ypsilophora (Hydrachnellae,Acari) Inhabiting Anodonta cygnea (Unionidae)

The co-occurring freshwater mussels Anodonta cygnea and A. anatina serve as hosts for the water mites Unionicola ypsilophora and U. intermedia, respectively. Male U. ypsilophora display a territorial behaviour. They fight with other males, and as a result, there is usually only one male per host. As a consequence, this intrasexual aggression results in female-defence polygyny, or a harem mating system. In contrast, U. intermedia shows no antagonistic behaviour between males. A. cygnea can serve as a host for U. intermedia, but this mite species apparently is excluded from the mussel by U. ypsilophora. In this way, U. intermedia is restricted by competitive exclusion to the mussel A. anatina.