Photoperiodic induction of diapause in the spider mite Tetranychus urticae: qualitative or quantitative time measurement?

Abstract. Insects and mites may measure photoperiods eitfier by classifying them as long or short relative to a critical value (qualitative time measurement) or by using the absolute value (quantitative time measurement). The spider mite Tetranychus urticae is thought to use a qualitative mechanism of time measurement. In this paper we present the results of experiments with an inbred line of the spider mite (to keep genetic variation in photoperiodic responses small), to test whether quantitative aspects also play a role. Differences in diapause incidence in different long-night photoperiods at different temperatures may be an indication of quantitative responses to photoperiod. The effect of temperature on the photoperiodic response curve was studied at 16^oC, 19^oC and 22^oC. The response curves appeared to be similar at 16^oC and 19^oC, with a critical nightlength between 10 and 11 h. At 22^oC, diapause induction was less than 100% in all long-night regimens and die critical nightlength had shifted to 12 h. Maximum diapause induction (93%) occurred in a light-dark cycle with a 16 h dark phase (LD 8:16 h). Diapause induction was lowest in long-night photoperiods with dark phases of 20 h and longer. The number of light-dark cycles needed for 50% diapause induction at 19^oC varied. between 12.1 and 14.7 for LD 6:18 h, between 10.9 and 12.5 for LD 8:16 h, between 10.6 and 11.6 for LD 10:14 h, and between 10.1 and 10.7 for LD 12:12 h. Independent of die light-dark regimen, diapause induction took place in some individuals after receiving 8 cycles and virtually all individuals entered diapause after 16 cycles. No effect was found of the photoperiodic treatment during prediapause development (LD 6:18 h, LD 8:16 h, LD 10:14 h, LD 12:12 h) on diapause duration. The average diapause duration at LD 10:14 h and 19^oC was 61 days over all four treatments. We explained the results by hypothesising that nightlengths are assessed qualitatively and mat the photoperiodic clock operates more accurately near the critical nightlength.     

Inheritance of resistance to the two-spotted spider mite from L. pimpinellifolium (Jusl.) Mill. accession ‘TO-937’

The two-spotted spider mite (Tetranychus urticae Koch) is an important pest of tomato (Lycopersicon esculentum Mill.) crops in temperate regions as this spider mite has a very large capacity for population increase and causes severe tomato yield losses. There is no described tomato cultivar fully resistant to this pest, although resistant accessions have been reported within the green-fruited tomato wild species L. pennellii (Corr.) D’Arcy and L. hirsutum Humb. & Bonpl. We observed a L. pimpinellifolium (Jusl.) Mill. accession, ‘TO-937’, which seemed to be completely resistant to mite attacks and we crossed it with the susceptible L. esculentum cultivar. ‘Moneymaker’ to obtain a family of generations consisting of the two parents, the F₁, the F₂, the BC₁ to L. esculentum, and the BC₁ to L. pimpinellifolium. This family was evaluated for mite resistance in a polyethylene greenhouse using an experimental design in 60 small complete blocks distributed along 12 double rows. Each block consisted of five F₂ plants in one row and one plant of each of the two parents, the F₁, the BC₁ to L. esculentum, and the BC₁ to L. pimpinellifolium in the adjacent row. Plants at the 10–15 leaf stage were artificially infested by putting on them two pieces of French bean leaf heavily infested with T. urticae. After two months, evaluations of infestation were made by visual observation of mite nets and leaf damage. Plants that were free of signs of mite reproduction on the top half were considered as resistant, plants with silky nets only on their basal leaves, intermediate, and plants with mite reproduction on both basal and top canopies were scored as susceptible. Dominance for resistance appeared because all the ‘To-937’, BC₁ to L. pimpinellifolium, and F₁ plants were resistant. Not all ‘Moneymaker’ plants behaved as susceptible because 35% of plants were intermediate. In the BC₁ to L. pimpinellifolium and the F₂, most plants were scored as resistant, only 7 % BC₁ and 3 % F₂ plants were intermediate, and a single F₂ plant (0.3 %) was susceptible. With these figures, resistance seemed to be controlled by either four or two genes according to whether segregation in the BC₁ or in the F₂, respectively, were considered. These results could in part be explained because of appearance of negative interplot interference due to the high frequency of resistant genotypes within most of the generations. Therefore, the family was evaluated again but using a different experimental design. In the new experiment, 16 ‘TO-937’, 17 ‘Moneymaker’, 17 F₁, 37 BC₁ to L. pimpinellifolium, 38 BC₁ to L. esculentum, and 125 F₂ plants were included. Each of these test plants was grown besides a susceptible ‘Moneymaker’ auxilliary plant that served to keep mite population high and homogeneous in the greenhouse. Negative interplot interference was avoided with this design and all the ‘TO-937’, F₁, and BC₁ to L. pimpinellifolium plants were resistant, all ‘Moneymaker’ test plants were susceptible, and 52 % BC₁ to L. esculentum and 25 % F₂ plants were susceptible, which fitted very well with the expected for resistance governed by a single dominant gene. The simple inheritance mode found will favour sucessful introgression of mite resistance into commercial tomatoes from the very close relative L. pimpinellifolium.     

On the origin of the supernumerary chromosome in autosomal trisomies — with special reference to Down's syndrome

Summary The differential staining methods for chromosomes have led to the demonstration of more chromosomal polymorphisms. Not rarely, these polymorphisms allow in autosomal trisomies the detection of parental origin of the supernumerary chromosome. In addition, the malsegregation may be ascribed to 1st or 2nd meiotic division in informative families.This approach of analyzing possible causes of trisomies is subject to a considerable bias. Trisomic phenotypes are twice as frequent for 2nd meiotic errors than for 1st meiotic errors. Also, rare chromosome variants seldom occur in matings where malsegregation in 1st meiotic division can be detected. In the present paper this bias is analyzed mathematically on the family as well as on the population level.From this mathematical analysis and from the data in the literature we conclude that Down's syndrome as a whole is caused about 5–10 times more often by a malsegregation in 1st meiotic than by an error in 2nd meiotic division.Mainly from experimental studies in rodents, causes for errors in 1st and 2nd meiotic division are becoming apparent. They are summarized in the context of the results of the present paper.Human population cytogenetics, a subject originated by Court Brown, has not, as yet, required mathematics at all unless we include—as I think we may correctly—the exact study of such variables as parental age and chromosomal measurements. L. S. Penrose (1970)We dedicate this paper to Professor Emeritus P. E. Becker, M.D., with our best wishes for his retirement.     

Embryogenesis of an embryonic lethal, ‘kidney-shaped egg’ in Bombyx mori,with special reference to mesoderm differentiation

Summary

Within the kidney-shaped egg laid by the homozygous female, the embryo develops only ectodermal organs, but no mesodermal organs. The early embryogenesis of this strain was examined with light and electron microscopy. Until the early germband stage no remarkable differences are distinguishable between the normal and the kidney-shaped eggs. Afterwards, in the kidney-shaped egg large amount of cytoplasmic masses and often several cells are extruded from the presumptive head region into the yolk at the ‘pyriform’ stage, resulting in inhibiting the formation of a normal wide head lobe and an invagination occurring in its central region, the first sign of the mesoderm differentiation. This phenomenon proceeds gradually toward the posterior part and thus the differentiation of mesoderm becomes impossible throughout the entire length of germband. The results are discussed in the context of the mesoderm differentiation in Bombyx.     

The possibilities for control of two‐spotted spider mite Tetranychus urticae on field‐grown strawberries in the UK by predatory mites

The potential of two species of predatory phytoseiid mites to control the two‐spotted spider mite, Tetranychus urticae, on unprotected field‐grown strawberries in the UK was investigated. Typhlodromus pyri, a native species, was able to control T. urticae in some circumstances, but was less effective under hot, dry conditions. Natural colonization by this species is likely to be too slow in plantations of 1–2 years life. Attempts to introduce this predator to strawberry fields on cut apple shoots were unsuccessful. The exotic predator Phytoseiulus persimilis, which is available from commercial sources, gave very good control of T. urticae when released onto strawberry plants in June. A release earlier in the year was less successful, so to prevent early build‐up of mites and possible plant damage it may sometimes be necessary to reduce spider mite numbers early in the year with an acaricide, before a later release of P. persimilis. The success of this integrated control strategy was demonstrated.     

Plant spatial distribution and predator–prey ratio affect biological control of the twospotted spider mite Tetranychus urticae (Acari: Tetranychidae) by the predatory mite Phytoseiulus persimilis (Acari: Phytoseiidae)

A greenhouse experiment was conducted to determine the effect of plant spacing and predator–prey ratio on dispersal and foraging efficiency of the predatory mite, Phytoseiulus persimilis, on the twospotted spider mite, Tetranychus urticae. When predators were released at the end of spider mite-infested arrays of lima bean plants that had either no spacing or two different patterns of spacing among plant rows, plant damage was uniformly low throughout the experiment at both predator–prey ratios (1:10 and 3:10) in the treatment with no spacing. In contrast, damage was higher in both treatments where plant rows were interrupted by spacing. At the 1:10 ratio, more plants closer to the predator release point experienced moderate damage than at the 3:10 ratio where only the plant rows farthest from the release point had unacceptable damage. Our findings suggest that point releases of P. persimilis at the standard 1:10 predator–prey ratio should be effective within a diameter of at least 65?cm on mite-infested patches of plants where pots are touching. However, if gaps in plant rows exist, even large numbers of predators may not be sufficient to protect parts of the crop unless predators are released at shorter fixed points in the greenhouse crop.     

Comprehensive analysis of the roles of ‘black’ and ‘gray’ clusters in structure and function of rat β-parvalbumin

Recently we found two highly conserved structural motifs in the proteins of the EF-hand calcium binding protein family. These motifs provide a supporting scaffold for the Ca²⁺ binding loops and contribute to the hydrophobic core of the EF-hand domain. Each structural motif forms a cluster of three amino acids called cluster I (‘black’ cluster) and cluster II (‘grey’ cluster). Cluster I is much more conserved and mostly incorporates aromatic amino acids. In contrast, cluster II includes a mix of aromatic, hydrophobic, and polar amino acids. The ‘black’ and ‘gray’ clusters in rat β-parvalbumin consist of F48, A100, F103 and G61, L64, M87, respectively. In the present work, we sequentially substituted these amino acids residues by Ala, except Ala100, which was substituted by Val. Physical properties of the mutants were studied by circular dichroism, scanning calorimetry, dynamic light scattering, chemical crosslinking, and fluorescent probe methods. The Ca²⁺ and Mg²⁺ binding affinities of these mutants were evaluated by intrinsic fluorescence and equilibrium dialysis methods. In spite of a rather complicated pattern of contributions of separate amino acid residues of the ‘black’ and ‘gray’ clusters into maintenance of rat β-parvalbumin structural and functional status, the alanine substitutions in the cluster I cause noticeably more pronounced changes in various structural parameters of proteins, such as hydrodynamic radius of apo-form, thermal stability of Ca²⁺/Mg²⁺-loaded forms, and total energy of Ca²⁺ binding in comparison with the changes caused by amino acid substitutions in the cluster II. These findings were further supported by the outputs of computational analysis of the effects of these mutations on the intrinsic disorder predisposition of rat β-parvalbumin, which also indicated that local intrinsic disorder propensities and the overall levels of predicted disorder were strongly affected by mutations in the cluster I, whereas mutations in cluster II had less pronounced effects. These results demonstrate that amino acids of the cluster I provide more essential contribution to the maintenance of structuraland functional properties of the protein in comparison with the residues of the cluster II.     

Fine structure of the ‘Wulst’ region of the domestic fowl in organotypic cultures

Summary Parts of the Wulst region of the chick embryo brain were maintained for 39 days in vitro. Processes of adjacent glial cell form zonulae occludentes and desmosomal junctions in the uppermost stratum of the cultures. Subjacent to this layer, in the neuropil, axodendritic synapses are abundant. 10–20 m below the surface the perikarya of glial cells and neurons are found. The latter form small clusters, plasma membranes of contiguous cells being directly apposed to each other. Axosomatic synapses terminate on the perikarya. Occasionally one terminal synapses on two nerve cells simultaneously. Two types of cilia arise from basal bodies in the cytoplasm of nerve cells. Type I is a slender protrusion of about 0.5 m in diameter, extending into the neuropil. On transverse sections it displays a 9 + 0 pattern of organization of paired micro tubules proximally, and an 8 + 1 configuration more distally. The length of the cilium is approximately 7 m. Type II cilia also originate in the neuronal cytoplasm. The structure of the proximal portion is identical with that of type I cilia. Toward the tip, however, the type II cilium is characterized by a bulbous enlargement which is filled with loosely folded membranes. The fine structural details of this cilium correlate closely to the outer segments of retinal photoreceptor cells during differentiation. The possible role of a light receptor in the Wulst region of birds, controlling biological rhythms, is discussed. Acknowledgements. The authors wish to thank Mrs. H. Frenk for her expert assistance in tissue culture and electron microscopic techniques     

Neoseiulus idaeus (Acari: Phytoseiidae) as a potential biocontrol agent of the two-spotted spider mite, Tetranychus urticae (Acari: Tetranychidae) in papaya: performance on different prey stage – host plant combinations

Development, reproduction, and life table parameters of the phytoseiid mite Neoseiulus idaeus Denmark & Muma preying on various stages of Tetranychus urticae Koch fed on papaya or snap bean plant were studied at 25 ± 2°C, 77 ± 2% RH and 12L:12D photoperiod. Most characteristics of the predator, including the duration of the immature stages, preoviposition and oviposition periods, and female longevity did not differ significantly among the different food combinations. During the adult stage, N. idaeus females survived up to 14 days. The net reproductive rate, the mean generation time, and the intrinsic rate of natural increase of N. idaeus were very similar on all T. urticae stage – host plant combinations, ranging from 5.15 to 6.61 females, 10.15 to 12.62 days, and 0.150 to 0.168, respectively. These results indicate that T. urticae reared either on papaya or snap bean is an adequate prey for the development and reproduction of N. idaeus. Moreover, the current findings demonstrate that the host plant of T. urticae did not affect the predator. The implications of these results for the success of N. idaeus as a biological control agent of T. urticae in papaya orchards are discussed.     

Predatory mirids of the green apple aphidAphis pomi,the two-spotted spider miteTetranychus urticae and the European red mitePanonychus ULMI in apple orchards in Québec

The incidence of predation of eight species of predacious mirids (Hemiptera: Miridae) present in an apple orchard of Québec on the green apple aphid, two-spotted spider mite and European red mite were investigated. The daily consumption rates varied from 1–2 green apple aphids forHyaliodes vitripennis Say andCampylomma verbasci Meyer to 7–9 aphids forDeraeocoris fasciolus Knight andLepidopsallus minisculus Knight.H. vitripennis consumed significantly more mites than the other mirid species with 26 and 18 mites per day for the two-spotted spider mite and the European red mite respectively. The combined use ofH. vitripennis andL. minisculus is suggested for the control of phytophagous mites. This paper is contribution No. 335/91.06.02R, Research Station, Agriculture Canada, Saint-Jean-sur-Richelieu, Québec, Canada.     

Subtle behavioral variation in wild chimpanzees, with special reference to Imanishi’s concept of kaluchua

Here we consider the concept of kaluchua (a word adopted from the English culture) in group-living animals developed by Imanishi in the 1950s. He distinguished it from bunka (the Japanese equivalent to the English culture) because he thought that bunka had strong connotations of noble and intellectual human-like activities. Although he did not rigidly define kaluchua, his original concept of kaluchua was much broader than bunka and represented non-hereditary, acquired behavior that was acknowledged socially. However, instead of social life, complex feeding skills have often formed the central topic in the current studies of animal culture. In order to provide evidence that more subtle behavioral variations exist among wild chimpanzee (Pan troglodytes) populations, we directly compared the behaviors of two well-habituated chimpanzee groups, at Bossou and Mahale. During a 2-month stay at Bossou, M.N. (the first author) saw several behavioral patterns that were absent or rare at Mahale. Two of them, mutual genital touch and heel tap were probably customary for mature females and for mature males, respectively. Index to palm and sputter are still open to question. These subtle patterns occurred more often than tool use during the study period, suggesting that rarity is not the main reason for their being ignored. Unlike tool use, some cultural behavioral patterns do not seem to require complex skills or intellectual processes, and sometimes it is hard to explain the existence of such behaviors only in terms of function.     

The structure and function of ‘active zone material’ at synapses

The docking of synaptic vesicles on the presynaptic membrane and their priming for fusion with it to mediate synaptic transmission of nerve impulses typically occur at structurally specialized regions on the membrane called active zones. Stable components of active zones include aggregates of macromolecules, ‘active zone material’ (AZM), attached to the presynaptic membrane, and aggregates of Ca²⁺-channels in the membrane, through which Ca²⁺ enters the cytosol to trigger impulse-evoked vesicle fusion with the presynaptic membrane by interacting with Ca²⁺-sensors on the vesicles. This laboratory has used electron tomography to study, at macromolecular spatial resolution, the structure and function of AZM at the simply arranged active zones of axon terminals at frog neuromuscular junctions. The results support the conclusion that AZM directs the docking and priming of synaptic vesicles and essential positioning of Ca²⁺-channels relative to the vesicles'' Ca²⁺-sensors. Here we review the findings and comment on their applicability to understanding mechanisms of docking, priming and Ca²⁺-triggering at other synapses, where the arrangement of active zone components differs.     

Predation by Allothrombium pulvinum on the spider mites Tetranychus urticae and Amphitetranychus viennensis: Predation Rate, Prey Preference and Functional Response

The deutonymphs of Allothrombium pulvinum Ewing (Acari: Trombidiidae) are among the most important natural enemies of spider mites in North, North East and West Iran. In this study, maximum predation rate and preference experiments were conducted with A. pulvinum deutonymphs on apple leaf discs, to determine their preference for either of two spider mite species: Amphitetranychus viennensis (Zacher) and Tetranychus urticae Koch (Acari: Tetranychidae). Maximum predation rate tests showed that the predatory mite consumed more eggs and females of T. urticae than of A. viennensis. Furthermore, the Manly’s preference index for eggs and females of T. urticae confirmed that T. urticae were the preferred prey. The functional response of A. pulvinum deutonymphs on females of T. urticae was examined over a 24-h period. Predation of A. pulvinum deutonymphs presented with females of T. urticae followed a type III functional response. Estimated handling time for the predatory mites was 4.51 h and attack coefficient b, which describes the changes in attack rate with prey densities in a type III functional response, was 0.021.     

Parental strategy of the cichlid fish Perissodus microlepis,with particular reference to intraspecific brood ‘farming out’

Synopsis One parent was experimentally removed from brooding pairs of Perissodus microlepis in the field. The removal elicited drastic behavioural changes in the remaining parent and young. The remaining parent sometimes showed a sequence of peculiar behaviours which were not observed when guarding the young with its mate. Some left the brooding site with young in their mouths and then put the young under the care of another pair of brooding parents.     

Chemistry and biology of reactive species with special reference to the antioxidative defence status in pancreatic β-cells

BackgroundDiabetes mellitus is a serious metabolic disease. Dysfunction and subsequent loss of the β-cells in the islets of Langerhans through apoptosis ultimately cause a life-threatening insulin deficiency. The underlying reason for the particular vulnerability of the β-cells is an extraordinary sensitivity to the toxicity of reactive oxygen and nitrogen species (ROS and RNS) due to its low antioxidative defense status.Scope reviewThis review considers the different aspects of the chemistry and biology of the biologically most important reactive species and their chemico-biological interactions in the β-cell toxicity of proinflammatory cytokines in type 1 diabetes and of lipotoxicity in type 2 diabetes development.Major conclusionThe weak antioxidative defense equipment in the different subcellular organelles makes the β-cells particularly vulnerable and prone to mitochondrial, peroxisomal and ER stress.Looking upon the enzyme deficiencies which are responsible for the low antioxidative defense status of the pancreatic β-cells it is the lack of enzymatic capacity for H₂O₂ inactivation at all major subcellular sites.General significanceDiabetes is the most prevalent metabolic disorder with a steadily increasing incidence of both type 1 and type 2 diabetes worldwide. The weak protection of the pancreatic β-cells against oxidative stress is a major reason for their particular vulnerability. Thus, careful protection of the β-cells is required for prevention of the disease.