Range expansion of the small spruce bark beetle Ips amitinus: a newcomer in northern Europe

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Photoperiodic and temperature control of diapause induction and colour change in the southern green stink bug Nezara viridula

Abstract. The effect of photoperiod and temperature on the duration of the nymphal period, diapause induction and colour change in adults of Nezara viridula (L.) (Heteroptera: Pentatomidae) from Japan was studied in the laboratory. At 20 °C, the developmental period for nymphs was significantly shorter under LD 10 : 14 h (short day) and LD 16 : 8 h (long day) than under intermediate photoperiods, whereas at 25 °C it was slightly shorter under intermediate than short- and long-day conditions. It is assumed that photoperiod-mediated acceleration of nymphal growth takes place in autumn when day-length is short and it is unlikely that nymphal development is affected by day-length under summer long-day and hot conditions. Nezara viridula has an adult diapause controlled by a long-day photoperiodic response. At 20 °C and 25 °C in both sexes, photoperiodic responses were similar and had thresholds close to 12.5 h, thus suggesting that the response is thermostable within this range of temperatures and day-length plays a leading role in diapause induction. Precopulation and preoviposition periods were significantly longer under near-critical regimes than under long-day ones. Short-day and near-critical photoperiods induced a gradual change of adult colour from green to brown/russet. The rate of colour change was significantly higher under LD 10 : 14 h than under LD 13 : 11 h, suggesting that the colour change is strongly associated with diapause induction. The incidences of diapause or dark colour did not vary among genetically determined colour morphs, indicating that these morphs have a similar tendency to enter diapause and change colour in response to short-day conditions.     

Summer Diapause as a Special Seasonal Adaptation in Insects: Diversity of Forms,Control Mechanisms,and Ecological Importance

Insects living in the temperate climate include summer diapause, or aestivation, in their seasonal cycle to solve various problems related to adaptation to unfavorable seasons. Unlike winter diapause, summer diapause occurs in summer and is usually terminated in autumn when active feeding, development, and/or reproduction are restored. Typically, high temperature and long day induce summer diapause and then maintain it, whereas short day and low temperature prevent induction of this diapause or terminate it. The summer diapause syndrome is basically similar to that of winter diapause; it includes prior development of large fat body, decreased level of metabolism, increased general resistance to unfavorable abiotic and biotic conditions, etc. Inhibition of morphogenesis and gametogenesis is under the control of the endocrine system. The onset of summer diapause is often accompanied by migrations to varying, sometimes significant distances to the sites of aestivation. The selective factors responsible for evolution of summer diapause vary between insect species. Climatic factors and, consequently, availability and abundance of food, as well as pressure of predators and parasites are likely to be the main factors that stimulate its occurrence. In some species, prolonged diapause begins in spring or early summer and ceases only after over-wintering. When studied in detail, such prolonged diapause often turns out to be a sequence of two independent diapauses, summer and winter ones, occurring in succession without detectable external changes.     

Responses of insects to the current climate changes: from physiology and behavior to range shifts

Climate change (first of all the rise in temperature) is currently considered one of the most serious global challenges facing mankind. Here we review the diversity of insect responses to the current climate warming, with particular focus on true bugs (Heteroptera). Insects as ectotherms are bound to respond to the temperature change, and different species respond differently depending on their specific physiological and ecological traits, seasonal cycle, trophic relations, etc. Insect responses to climate warming can be divided into six categories: changes in (1) ranges, (2) abundance, (3) phenology, (4) voltinism, (5) morphology, physiology, and behavior, and (6) relationships with other species and in the structure of communities. Changes in ranges and phenology are easier to notice and record than other responses. Range shifts have been reported more often in Lepidoptera and Odonata than in other insect orders. We briefly outline the history and eco-physiological background of the recent range limit changes in the Southern green stink bug Nezara viridula (Heteroptera, Pentatomidae) in central Japan. Range expansion in individual species can lead to enrichment of local faunas, especially at high latitudes. Phenological changes include not only advances in development in spring but also shifts in phenology later in the season. The phenophases related to the end of activity usually shift to later dates, thus prolonging the period of active development. This may have both positive and negative consequences for the species and populations. As with any other response, the tendencies in phenological changes may vary among species and climatic zones. The proven cases of change in voltinism are rare, but such examples do exist. Application of models based on thermal parameters of development suggests that a rise in temperature by 2°C will result in an increased number of annual generations in many species from different arthropod taxa (up to three or four additional generations in Thysanoptera, Aphidoidea, and Acarina). The warming-mediated changes in physiology, morphology, or behavior are difficult to detect and prove, first of all because of the absence of reliable comparative data. Nevertheless, there are examples of changes in photoperiodic responses of diapause induction and behavioral responses related to search of shelters for summer diapause (aestivation). Since (1) individual species do not exist in isolation and (2) the direction and magnitude of responses even to the same environmental changes vary between species, it may be expected that in many cases the current stable relationships between species will be affected. Thus, unequal range shifts in insects and their host plants may disrupt their trophic interactions near the species?? range boundaries. Studies of responses to climate warming in more than one interrelated species or in entire communities are extremely rare. The loss of synchronism in seasonal development of community members may indicate inability of the higher trophic levels to adapt fully to climate warming or an attempt of the lower trophic level to escape from the pressure of the higher trophic levels. It is generally supposed that many insect species in the Temperate Climate Zone will benefit in some way from the current climate warming. However, there is some experimental evidence of an opposite or at least much more complex response; the influence of warming might be deleterious for some species or populations. It is suggested that species or populations from the cold or temperate climate have sufficient phenotypic plasticity to survive under the conditions of climate warming, whereas species and populations which already suffer from stress under extreme seasonal temperatures in warmer regions may have a limited ??maneuver space?? since the current temperatures are close to their upper thermal limits. Without genetic changes, even moderate warming will put these species or populations under serious physiological stress. The accumulated data suggest that responses of insects and the entire biota to climate warming will be complex and will vary depending on the rate of warming and ecological peculiarities of species and regions. Physiological responses will vary in their nature, direction, and magnitude even within one species or population, and especially between seasons. The responses will also differ in different seasons. For example, warming may negatively affect nymphal development during the hot season but at the same time accelerate growth and development during the cold season and/or ensure milder and more favorable overwintering conditions for adults. All these factors will affect population dynamics of particular species and relationships among the members of ecosystems. We should keep in mind that (1) not only selected insect species but almost all the species will be affected, (2) temperature is not the only component of the climatic system that is changing, and (3) responses will be different in different seasons. Host plants, phytophagous insects, their competitors, symbionts, predators, parasites, and pathogens will not only respond separately to climate changes; individual responses will further affect the responses of other species, thus making reliable prediction extremely complicated. Responses are expected to (1) be species- or population-specific, (2) concern basically all the aspects of organism/ species biology and ecology (individual physiology, population structure, abundance, local adaptations, phenology, voltinism, and distribution), and (3) occur at scales ranging from an undetectable cellular level to major distribution range shifts or regional extinctions. The scale of insect responses will depend on the extent and rate of climate warming. Slight to moderate warming may cause responses only in a limited number of species with more flexible life cycles, whereas a substantial increase in temperature may affect a greater number of different species and ecological groups.     

Seasonal development and ecology of anthocorids (Heteroptera,Anthocoridae)

Seasonal development and ecology of Anthocoridae are reviewed. Most of 500–600 species in the family are predacious or zoo-phytophagous, and a few other species are exclusively phytophagous or myrmecophilous. Some anthocorids are (and many others can potentially be) used as biological control agents in the Integrated Pest Management (IPM). Overwintering at the adult stage is typical of anthocorid bugs from the temperate zone (especially for the subfamily Anthocorinae). The known exceptions are the embryonic diapause in Tetraphleps abdulghanii, Temnostethus pusillus, and T. gracilis (Anthocorinae) and continuous development through all seasons (a homodynamic seasonal cycle) in Lyctocoris campestris and some species of Xylocoris (Lyctocorinae). In a number of species, especially in the genera Anthocoris and Orius, copulation occurs before overwintering and only females survive winter, a feature very unusual for Heteroptera and insects in general. Many anthocorid species are multivoltine in the temperate zone, producing several (up to 8 in some cases) generations per year. The number of generations typically decreases to 1 per year towards the north. Seasonal development of multivoltine species is chiefly controlled by daylength and temperature. All multivoltine anthocorids of the temperate zone studied to date have photoperiodic response of a long-day type: the females reproduce under the long-day conditions, but enter diapause under the short-day conditions. Towards the south, the photoperiodic response gradually becomes weaker: some populations do not enter diapause even under the short-day conditions, especially at higher temperatures. Termination of diapause is poorly understood in anthocorids, but a number of species require low-temperature treatment for a few weeks prior to the start of oviposition. Alary and color polymorphism are rare in the family, and they have never been shown to be seasonal or environmentally controlled. Pronounced seasonal migrations and aggregation behavior also have never been reported in Anthocoridae. Summer diapause appears to be very unusual for the family, having been reported only in Tetraphleps abdulghanii. The seasonal change of host plants, known in some populations of Anthocoris nemorum and A. nemoralis, is also a seasonal adaptation unusual for Heteroptera. Seasonality of tropical and subtropical species is poorly studied, but anthocorids developing without winter diapause are considered promising agents for the biological control of arthropod pests. Further studies of ecophysiology of Anthocoridae will optimize application and mass rearing of these predators in IPM programs.     

Timing of diapause induction outside the natural distribution range of a species: an outdoor experiment with the bean bug Riptortus clavatus

The phytophagous bug Riptortus clavatus (Thunberg) (Heteroptera: Alydidae) produces two or three generations per year in Central Japan and overwinters in the adult stage. In bugs from the Kyoto population (35°00 N, 135°45 E), we studied (1) the effects of day-length on the nymphal and preoviposition periods under constant photoperiod at 20.5 °C, and (2) photoperiodic induction of adult diapause at 20.5 °C and under a combination of constant photoperiod and natural daily rhythm of temperature in the forest-steppe zone of Russia (50°38 N, 35°58 E). Then, we examined (3) the timing of diapause induction under quasi-natural conditions in the same region, far outside the species' natural geographical range. At 20.5 °C, the nymphal period in both males and females was significantly longer under regimes with shorter photophases than under those with longer photophases. The preoviposition period in females was significantly longer under the near-critical long-day regime L14:D10 than under typical long-day regimes (L15:D9, L16:D8, and L17:D7). The critical day-length for diapause induction was shorter under conditions of natural daily rhythm of temperature than those reported at constant 20, 25, and 30 °C. Under quasi-natural conditions in the forest-steppe zone, R. clavatus entered diapause in September, much later than the local populations of true bugs studied to date. This experiment showed that R. clavatus was maladapted to new environmental conditions: diapause was induced too late with the result that all or most nymphs hatched in late August or early September will die.     

Seasonal Development of Plant Bugs (Heteroptera,Miridae): Subfamily Mirinae,Tribe Stenodemini

Entomological Review - The seasonal adaptations of 8 better studied species belonging to 4 genera of the tribe Stenodemini are analyzed. A univoltine seasonal cycle with obligate diapause is...     

Obligate association with gut bacterial symbiont in Japanese populations of the southern green stinkbug <Emphasis Type="Italic">Nezara viridula</Emphasis> (Heteroptera: Pentatomidae)

The southern green stinkbug Nezara viridula (Linnaeus) has a number of sac-like outgrowths, called crypts, in a posterior section of the midgut, wherein a specific bacterial symbiont is harbored. In previous studies on N. viridula from Hawaiian populations, experimental elimination of the symbiont caused few fitness defects in the host insect. Here we report that N. viridula from Japanese populations consistently harbors the same gammaproteobacterial gut symbiont, but, in contrast with previous work, experimental sterilization of the symbiont resulted in severe nymphal mortality, indicating an obligate host–symbiont relationship. Considering worldwide host–symbiont association and these experimental data, we suggest that N. viridula is generally and obligatorily associated with the gut symbiont, but that the effect of the symbiont on host biology may be different among geographic populations. Possible environmental factors that may affect the host–symbiont relationship are discussed.