Phenotypic plasticity in a complex world: interactive effects of food and temperature on fitness components of a seed beetle

Most studies of phenotypic plasticity investigate the effects of an individual environmental factor on organism phenotypes. However, organisms exist in an ecologically complex world where multiple environmental factors can interact to affect growth, development and life histories. Here, using a multifactorial experimental design, we examine the separate and interactive effects of two environmental factors, rearing host species (Vigna radiata, Vigna angularis and Vigna unguiculata) and temperature (20, 25, 30 and 35°C), on growth and life history traits in two populations [Burkina Faso (BF) and South India (SI)] of the seed beetle, Callosobruchus maculatus. The two study populations of beetles responded differently to both rearing host and temperature. We also found a significant interaction between rearing host and temperature for body size, growth rate and female lifetime fecundity but not larval development time or larval survivorship. The interaction was most apparent for growth rate; the variance in growth rate among hosts increased with increasing temperature. However, the details of host differences differed between our two study populations; the degree to which V. unguiculata was a better host than V. angularis or V. radiata increased at higher temperatures for BF beetles, whereas the degree to which V. unguiculata was the worst host increased at higher temperatures for SI beetles. We also found that the heritabilities of body mass, growth rate and fecundity were similar among rearing hosts and temperatures, and that the cross-temperature genetic correlation was not affected by rearing host, suggesting that genetic architecture is generally stable across rearing conditions. The most important finding of our study is that multiple environmental factors can interact to affect organism growth, but the degree of interaction, and thus the degree of complexity of phenotypic plasticity, varies among traits and between populations.     

Responses of an oligophagous beetle species to rearing for several generations on alternative host‐plant species

1. Imprinting and rearing on alternative host‐plant species over several generations may affect performance and preferences of herbivorous insects. In this study, the adjustment potential to alternative hosts was investigated in the oligophagous beetle Phaedon cochleariae (F.) (Coleoptera: Chrysomelidae). 2. A population that had been reared for several generations on Brassica rapa was split and transferred to either one of the alternative Brassicaceae species, Sinapis alba and Nasturtium officinale, or was kept on B. rapa for continuous rearing. After 10 generations, a subset of the Sinapis and Nasturtium populations was tested again on the original host species, B. rapa. Larval performance and adult preferences were tested. 3. In the second generation, beetles performed better (higher body mass and faster larval development) on B. rapa than on the two alternative species. No evidence for imprinting was found. After 10 generations of selection on the alternative plant species, the performance of the beetles on these species improved. This effect was more pronounced on S. alba than on N. officinale. However, the performance on B. rapa after 10 generations of selection on the alternative species was unaffected, and was nearly equal to the insects kept continuously on B. rapa, with slight deviations only in the lines selected on N. officinale. 4. Most females preferred to oviposit on B. rapa independent of their experience, suggesting a genetic fixation and/or a positive relationship between larval performance and adult preference. Preferences may have been also driven by physical leaf characteristics.     

Volatile and Contact Chemicals Released by Nezara viridula (Heteroptera:Pentatomidae) Have a Kairomonal Effect on the Egg Parasitoid Trissolcus basalis (Hymenoptera: Scelionidae)

The responses of females of the egg parasitoid Trissolcus basalis (Wollaston) (Hymenoptera: Scelionidae) to volatile and contact chemicals from its host Nezara viridula (L.) (Heteroptera: Pentatomidae) were investigated in a Y-tube olfactometer and under open arena conditions. In the Y-tube tests, volatiles from virgin males and from females in a preovipositional state attracted T. basalis females, while volatiles from host virgin females did not. In an open arena, traces left by N. viridula adults in different physiological conditions function as contact cues inducing the wasps to remain longer in the arena and to change the pattern of their walking behavior. However, only contact kairomones from N. viridula mated females in a preovipositional condition induced an arrestment response characterized by an increase in patch searching time and turning rates and a reduction in linear speed. The chemical ecological implications of these results on this host–parasitoid association are discussed.     

Control of preimaginal development by photoperiod and temperature in the dock leaf beetle <Emphasis Type="Italic">Gastrophysa viridula</Emphasis> (De Geer) (Coleoptera,Chrysomelidae)

Development times of preimaginal stages and immature adult body mass of the dock leaf beetle Gastrophysa viridula from Bryansk (53°N, 34°E) were determined at six constant temperatures ranging from 16 to 26°C and at two photoperiods, 12L: 12D or 22L: 2D. The lower developmental threshold (LDT) and sum of degreedays (SDD) were calculated for eggs, larvae, and pupae; the values for the total preimaginal development were 7.9°C and 274.8 °C×d, respectively. The thermal reaction norms for preimaginal development were not affected by photoperiod, although the adult body mass was on average greater under short-day conditions. Our results confirm the previously published data on G. viridula concerning diapause induction by shorter daylengths, greater body mass under lower temperatures, and narrowing of the thermal optimum range during preimaginal development. The thermal reaction norms for larval development were shown to be the same in individuals that died during the pupal stage, and in those that successfully emerged as adults. Our results are more precise than the previous data on this species due to a larger sample size, careful control of rearing conditions, and the use of an alternative method for calculating LDT and SDD. In particular, a more accurate estimation of LDTs allowed us to demonstrate that rate isomorphy was violated in this species, contrary to what had been stated by Honěk and co-authors (2003).     

Behavioral response of the egg parasitoid <Emphasis Type="Italic">Ooencyrtus telenomicida</Emphasis> to host-related chemical cues in a tritrophic perspective

The response of the generalist egg parasitoid Ooencyrtus telenomicida (Vassiliev) (Hymenoptera: Encyrtidae) to host-related chemical cues from tomato plants, Solanum lycopersicum L., and adults of Nezara viridula (L.) (Heteroptera: Pentatomidae) was investigated in laboratory-based no-choice and paired-choice tests. In Y-tube olfactometer experiments, when female wasps were exposed to volatiles from plants in different conditions, they were attracted only to volatiles produced by N. viridula adult-infested tomato plants. When female wasps were exposed to adults of N. viridula, they were attracted to volatiles from virgin males, and, at a lower level, to volatiles from mated females in preoviposition state. Finally, studies in open arena showed that chemical footprints left by adults of N. viridula did not induce arrestment responses in wasp females. These results are discussed in terms of extrinsic competition with other beneficial egg parasitoids that in field can compete for the same egg mass, since intraguild interactions may affect the success of a biological control program.     

Darkling Beetles (Alphitobius diaperinus) and Their Larvae as Potential Vectors for the Transfer of Campylobacter jejuni and Salmonella enterica Serovar Paratyphi B Variant Java between Successive Broiler Flocks

Broiler flocks often become infected with Campylobacter and Salmonella, and the exact contamination routes are still not fully understood. Insects like darkling beetles and their larvae may play a role in transfer of the pathogens between consecutive cycles. In this study, several groups of beetles and their larvae were artificially contaminated with a mixture of Salmonella enterica serovar Paratyphi B Variant Java and three C. jejuni strains and kept for different time intervals before they were fed to individually housed chicks. Most inoculated insects were positive for Salmonella and Campylobacter just before they were fed to the chicks. However, Campylobacter could not be isolated from insects that were kept for 1 week before they were used to mimic an empty week between rearing cycles. All broilers fed insects that were inoculated with pathogens on the day of feeding showed colonization with Campylobacter and Salmonella at levels of 50 to 100%. Transfer of both pathogens by groups of insects that were kept for 1 week before feeding to the chicks was also observed, but at lower levels. Naturally contaminated insects that were collected at a commercial broiler farm colonized broilers at low levels as well. In conclusion, the fact that Salmonella and Campylobacter can be transmitted via beetles and their larvae to flocks in successive rearing cycles indicates that there should be intensive control programs for exclusion of these insects from broiler houses.     

Distribution, host specificity, and overwintering of Celatoria bosqi Blanchard (Diptera: Tachinidae), a South American parasitoid of Diabrotica spp. (Coleoptera: Chrysomelidae: Galerucinae)

The genus Diabrotica (Coleoptera: Chrysomelidae) includes a great number of pest species, including some of the most important crops pests of the Americas. However, only five parasitoid species have been recorded for it. The parasitoid Celatoria bosqi Blanchard was the first parasitoid described from Diabrotica spp. in South America, where substantial parasitism has been observed. C. bosqi has been collected almost throughout the South American distribution of its main host, Diabrotica speciosa (Germar), in an area that includes temperate and tropical lowlands, and semiarid to humid highlands. Three Diabrotica species were found to host the parasitoid, D. speciosa (Germar), Hystiopsis sp., and Diabrotica viridula (F.), with a total parasitism of 2.60, 5.55, and <0.02%, respectively. Laboratory experiments with field beetles and puparia, reared in the laboratory, indicate that C. bosqi overwinters obligatorily in overwintering adult host beetles, remaining quiescent in its live host below developmental temperatures. Based on the known climatic range of C. bosqi, and its requirement of adult overwintering hosts, a potential distribution in North America is projected.     

Surviving winter: diapause syndrome in the southern green stink bug Nezara viridula in the laboratory,in the field,and under climate change conditions

The southern green stink bug Nezara viridula (L.) (Heteroptera: Pentatomidae) has long attracted attention not only as a serious pest of numerous agricultural crops, but also as a species expanding its range in many parts of the world. Nezara viridula has also been widely used as a model in different experimental studies. The present review focuses on reproductive (i.e. adult) winter diapause, which is the pivotal element of the species' seasonal cycle. Results from numerous field experiments and observations, as well as laboratory ecophysiological investigations conducted during the few last decades, are analyzed and interpreted. Experimental findings are used to describe in detail the dynamics of physiological changes during overwintering. Reproductive diapause in N. viridula is controlled in both sexes by photoperiodic conditions. The induction of diapause is associated with a reversible change of body colour from green or yellow to russet (or brown). The proper timing of adult emergence and the induction of diapause, as well as the size of adults, is vitally important for successful overwintering. Nezara viridula has been shown to respond strongly to the current trend in climate change by shifting the limit of its northern range, particularly in central Japan. Analysis of historic climate data suggests that the environmental conditions during the last few decades have become more favourable for the overwintering survival of N. viridula in many locations in central Japan. This has likely promoted the northward spread of the species. The relationships between reproductive diapause, reversible body colour change, overwintering success and the recent range expansion are analyzed. Perspectives of the range dynamics of the species are discussed in light of further predicted climate change.     

Within-species variation among populations of the Carex flava complex as a function of habitat conditions

Background: Variable habitat conditions contribute to morphological variability that plays a substantial part in evolution of plants. Understanding the extent of phenotypic plasticity has important implication for assigning individuals to taxa.

Aims: I analysed morphological variability among populations within species of the Carex flava group and tested to what extent morphological variability was associated with habitat conditions.

Methods: A total of 571 specimens from 20 populations of four species from the C. flava complex were sampled in Poland and tested by Discriminant Function Analysis (DFA). The relationship between morphological characters and habitat factors was explored by means of the redundancy analysis (RDA).

Results: Variability of the generative and vegetative traits was fairly similar in Carex lepidocarpa, C. flava and Carex demissa, while it was somewhat higher in Carex viridula. The morphological traits were mostly related to soil organic matter content, calcium and carbonate, as well as to habitat fertility (C:N ratio), elevation and habitat disturbance. The results obtained do not support the separation of C. viridula var. pulchella from C. viridula var. viridula.

Conclusions: Phenotypic variability in the species of the C. flava complex is related to habitat conditions and this can lead to the differentiation of morphotypes within species.     

Artificial diets for rearing the coconut hispine beetle,Brontispa longissima (Coleoptera: Chrysomelidae), and their suitability to two specialist parasitoids

The coconut hispine beetle, Brontispa longissima (Gestro), is a serious invasive pest that infests young unopened fronds of coconut palms (Cocos nucifera L.) in Southeast Asia. We previously developed the first artificial diet for rearing B. longissima larvae, which contained a leaf powder of young coconut fronds. Because the fronds are required for healthy growth of coconut palms, it is necessary to reduce their use for rearing the beetles. In this study, we tested two new artificial diets for the beetle larvae, which contained the leaf powders of mature coconut leaves or orchard grass (Dactylis glomerata L.). Brontispa longissima successfully developed from hatching to adulthood on both the mature coconut leaf diet and orchard grass diet. The beetles reared on the mature coconut leaf diet and orchard grass diet developed faster than those reared on the young coconut leaf diet. Fecundity and egg hatchability of beetles did not differ among the three diet treatments. We then examined the suitability of beetle larvae or pupae reared on each diet as hosts for two specialist endoparasitoids, Asecodes hispinarum Boucek and Tetrastichus brontispae Ferriere. The survival rate from oviposition to adult emergence for A. hispinarum was 43.8% in hosts reared on a young coconut leaf diet, 77.1% on a mature coconut leaf diet, and 85.7% on an orchard grass diet. For T. brontispae, the survival rate was 70.0% in hosts reared on the young coconut leaf diet, 38.1% on the mature coconut leaf diet, and 66.7% on the orchard grass diet. Our results indicate these artificial diets can be useful for rearing B. longissima and its two parasitoids, helping to reduce the costs of mass rearing these insects.     

Male-mediated aggregation of male, female and 5th-instar southern green stink bugs and concomitant attraction of a tachinid parasite,Trichopoda pennipes

In 124 days of field tests, 88.7% of male, 87.3% of female, and 90.2% of 5th-instarNezara viridula were caught on cages containing maleN. viridula rather than on female or control cages. Likewise, 92% of the female and 86% of the male parasite,Trichopoda pennipes (F.), were caught on cages containing maleN. viridula. Attraction ofN. viridula occurs throughout the daylight hours, but is strongest in a 5-min period immediately prior to complete darkness. The data suggest the presence of a male-emitted aggregation pheromone inN. viridula, acting concomitantly as a kairomone forT. pennipes females.

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Zusammenfassung Es wurden im Sommer und Herbst Käfige auf Feldern verschiedener Kulturpflanzen aufgestellt. In jeden Käfig wurdenNezara viridula (Hemiptera: Pentatomidae)-Imagines eingesetzt, die geschlechtsweise so sortiert waren, dass jeder Käfig ausschliesslich Weibchen, ausschliesslich Männchen, oder gleiche Mengen beider Geschlechter enthielt. FreilebendeN. viridula wurden von den eingesperrten Insekten angelockt. Jeweils über 87% der Männchen, Weibchen und der Altlarven, die angezogen wurden, kamen an die Käfige die Männchen enthielten. Die SchmarotzerfliegeTrichopoda pennipes (Diptera: Tachinidae) wurde auch angelockt — hier fanden sich 92% der weiblichen und 86% der männlichen Fliegen auf den Käfigen, die männliche Wanzen enthielten. Die Anlockung der Hemipteren dauerte den ganzen Tag an, mit einer vorübergehenden, aber sehr starken Zunahme direkt vor dem Einbruch der Dunkelheit. Wir nehmen an, dassN. viridula-Männchen ein Pheromon abgeben, das nicht nur Weibchen, sondern auch andere Männchen, Larven und auch Schmarotzerfliegen anzieht. Das Verhalten der Insekten blieb immer gleich in den beiden Jahreszeiten, und auch die verschiedenen Pflanzenarten hatten keinen Einfluss darauf.

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Nezara viridula (L.) (Hemiptera: Pentatomidae)

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Diptera: Tachinidae     

Seasonal body weight, lipid content, and impact of starvation and water stress on adult survivorship and longevity ofNezara viridula andEuschistus heros

Fresh and dry body weights (FW, DW) were greater for adult southern green stink bug,Nezara viridula (L.) than for the brown stink bug,Euschistus heros F. throughout the year in southern Brazil. FemalesN. viridula significantly increased FW and DW in late summer-early autumn, and during mid-spring; femaleE. heros did not show the same rates of increase in FW and DW. FemaleN. viridula were heavier than males, particularly during summer; however, female and maleE. heros were generally similar in weight.E. heros contained significantly greater amounts of lipid thanN. viridula, during mid-autumn to early-spring (April–September). Survivorship (%) and total longevity ofE. heros adults provided water only was greater (34.6–24.6 days, for females and males) than that forN. viridula (14.8–13.0 days); without water and food, longevity was drastically reduced (<7 days) for both species.     

Niche width and variation within and between populations in colonizing species (Carex flava group)

Summary Taxa of the Carex flava group in Switzerland show a trend towards increased colonizing ability (r-selection). High colonizing ability is correlated with a large fundamental but a small and discontinuous realized niche. It is argued that r-selected species with wide niches should be monomorphic with generalists rather than polymorphic with specialists since they have small effective population sizes in which high genetic variability cannot be maintained. The most r-selected taxon of the group, C. viridula spp. viridula, has indeed the lowest genetic variability within populations but, in ecologically important characters, expresses the highest plasticity. The taxonomically important characters (inflorescences) have high heritability and differences between populations of C. viridula ssp. viridula are probably much affected by genetic drift.     

Insects in a warmer world: ecological, physiological and life-history responses of true bugs (Heteroptera) to climate change

Focusing on the southern green stink bug, Nezara viridula (Pentatomidae), in central Japan the effects of climate change on true bugs (Insecta: Heteroptera) are reviewed. In the early 1960s, the northern edge of the species's distribution was in Wakayama Prefecture (34.1°N) and distribution was limited by the +5°C coldest month (January) mean temperature isothermal line. By 2000, N. viridula was recorded 70 km further north (in Osaka, 34.7°N). Historical climate data were used to reveal possible causes of the northward range expansion. The increase of mean and lowest winter month temperatures by 1–2°C in Osaka from the 1950s to the 1990s improved potential overwintering conditions for N. viridula. This promoted northward range expansion of the species. In Osaka, adult diapause in N. viridula is induced after mid‐September, much later than in other local seed‐feeding heteropterans. This late diapause induction results in late‐season ineffective reproduction: some females start oviposition in autumn when the progeny have no chance of attaining adulthood and surviving winter. Both reproductive adults and the progeny die. A period from mid‐September to early November represents a phenological mismatch: diapause is not yet induced in all adults, but it is already too late to start reproduction. Females that do not start reproduction but enter diapause in September have reduced postdiapause reproductive performance: they live for a shorter period, have a shorter period of oviposition and produce fewer eggs in smaller egg masses compared with females that emerge and enter diapause later in autumn. To some extent, N. viridula remains maladapted to Osaka environmental conditions. Ecological perspectives on establishment in recently colonized areas are discussed. A review of available data suggests that terrestrial and aquatic Heteroptera species respond to climate change by shifting their distribution ranges, changing abundance, phenology, voltinism, physiology, behaviour, and community structure. Expected responses of Heteroptera to further climate warming are discussed under scenarios of slight (<2°C) and substantial (>2°C) temperature increase.     

The Effect of Seasonal Changes on Nezara viridula (L.) (Hemiptera: Pentatomidae) and Trissolcus basalis (Wollaston) (Hymenoptera: Scelionidae) in Hawaii

The effect of seasonal changes in temperature and photoperiod on the interaction of Nezara viridula (Hemiptera: Pentatomidae) and its egg parasitoid Trissolcus basalis (Hymenoptera: Scelionidae) was investigated in the laboratory. We found no evidence of reproductive diapause in N. viridula under simulated Hawaiian summer and winter conditions. Further, although “diapause” coloration was obtained in the laboratory, it was not correlated with reproductive status. Studies of the survival of T. basalis provided with honey under the same simulated conditions showed that under summer conditions, only 2.1% of the female and 13.5% of the male population were still alive by 60 days. When provided with N. viridula egg masses at 30 days, 79.4% of the eggs were parasitized in a 3-h period. Under winter conditions, 54.3, 28.3, and 14.5% of the females were alive at 30, 60, and 90 days after adult emergence. When provided with N. viridula egg masses at 30, 60, and 90 days for 3 h, 57.6, 32.8, and 47.1% of the eggs were successfully parasitized. These studies suggest the limiting factor in the interaction of T. basalis and N. viridula is not reproductive diapause, but instead the ability of T. basalis to survive summer conditions.     

Comparison of the mating behaviour between two sympatric species,Nezara antennata andN. viridula (Heteroptera: Pentatomidae), with special reference to sound emission

Mating behaviour and associated songs were compared between 2 sympatric congeneric species,Nezara antennata andN. viridula, between which interspecific mating was known to occur under natural conditions. The fundamental sequence of mating behaviour for these species was the same. Three kinds of songs were recorded from each sex ofN. antennata. ForN. viridula, 4 kinds of male songs and 3 kinds of female songs were recorded. The songs which corresponded with definite behavioural bouts were distinct between these species. Some consideration was made as to why interspecific differences in the songs did not sufficiently engender ethological isolation. In addition, some geographic variations in the songs were shown among Yugoslavian (Čokl et al. 1972), American (Harris et al. 1982) and Japanese populations ofN. viridula. These variations were relatively inconspicuous when compared with the interspecific differences fromN. antennata.     

Some like it hot! Rapid climate change promotes changes in distribution ranges of Nezara viridula and Nezara antennata in Japan

We compared past and current limits of the distribution range of the southern green stink bug, Nezara viridula (L.) (Heteroptera: Pentatomidae), in central Japan. In the early 1960s, the northern limit of the range was in Wakayama Prefecture and was limited by a +5 °C isothermal line for the mean January temperature. In 2006–2007, a new survey demonstrated that this northern limit had shifted northwards by 85 km (i.e., at a mean rate of 19.0 km per decade). The shift was most likely promoted by milder winter conditions. The mean January to February temperature in the region was 1.03–1.91 °C higher in 1998–2007 than in 1960–1969. The number of cold days (with the mean temperature below +5 °C) also significantly decreased, while the annual lowest temperature significantly increased. Nezara viridula was found mostly close to those locations where (i) the mean January temperature exceeded +5 °C, (ii) the mean number of cold days did not exceed 26 in January to February, and (iii) where the mean annual lowest temperature did not drop below –3.0 °C. The general linear model shows that the mean January temperature and number of cold days are the most important factors controlling the northern limit of distribution of N. viridula. All the climatic data suggest that over the last 45 years, environmental conditions have become more favourable for overwintering of N. viridula at many locations in central Japan. This has probably promoted the northward spread of the species, representing a direct response to climate warming. A sympatrically distributed congeneric, Nezara antennata Scott, seems to respond to the warming by a retreat from the ocean coast towards cooler elevated habitats, which might be a complex response to elevated temperature and interspecific mating with N. viridula. It is suggested that the range changes in both species will continue in response to further climate change.     

Relative longevity of adult Nezara viridula in field cages of cotton,peanut, and soybean

Producers in the southeastern USA face significant crop losses from the stink bugs Nezara viridula (L.), Euschistus servus (Say), and Chinavia hilaris (Say) (all Hemiptera: Pentatomidae). Cotton, peanut, and soybean are major agronomic crops and host plants of stink bugs in the region. We conducted a field plot study to measure the relative longevity of adult, unmated N. viridula males and females caged on peanut, cotton, and soybean to test three hypotheses: (1) differences in mortality are associated with differences in host plant food suitability, (2) mortality rates increase with age, and (3) males have higher mortality than females. Using survival analysis, we found that the sex of the individual did not affect survival rates on any of the three host plants. Survival was significantly higher in cotton and soybean than in peanut. Mortality rates increased with age in peanut, but not in soybean or cotton. The frequency of canopy temperatures above 35 °C was higher in peanut than in soybean. Peanut appears to be a less than ideal habitat in terms of canopy temperature and/or food quality for N. viridula adults. Both, cotton and soybean were equally suitable food resources for N. viridula adults prior to maturation of the plants.     

Dissecting insect responses to climate warming: overwintering and post‐diapause performance in the southern green stink bug,Nezara viridula,under simulated climate‐change conditions

The effect of simulated climate change on overwintering and post‐diapause reproductive performance is studied in Nezara viridula (L.) (Heteroptera: Pentatomidae) close to the species' northern range limit in Japan. Insects are reared from October to June under quasi‐natural (i.e. ambient outdoor) conditions and in a transparent incubator, in which climate warming is simulated by adding 2.5°C to the ambient temperatures. Despite the earlier assumption that females of N. viridula overwinter in diapause, whereas males do so in quiescence, regular dissections show that the two sexes overwinter in a state of true diapause. During winter, both sexes are dark‐coloured and have undeveloped reproductive organs. Resumption of development does not start until late March. During winter, the effect of simulated warming on the dynamics and timing of physiological processes appears to be limited. However, the warming significantly enhances winter survival (from 27–31% to 47–70%), which is a key factor in range expansion of N. viridula. In spring, the effect of simulated warming is complex. It advances the post‐diapause colour change and transition from dormancy to reproduction. The earlier resumption of development is more pronounced in females: in April, significantly more females are already in a reproductive state under the simulated warming than under quasi‐natural conditions. In males, the tendency is similar, although the difference is not significant. Warming significantly enhances spring survival and percentage of copulating adults, although not the percentage of ovipositing females and fecundity. The results suggest that, under the expected climate‐warming conditions, N. viridula will likely benefit mostly as a result of increased winter and spring survival and advanced post‐diapause reproduction. Further warming is likely to allow more adults to survive the critical cold season and contribute (both numerically and by increasing heterogeneity) to the post‐overwintering population growth, thus promoting the establishment of this species in newly‐colonized areas.     

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.