Rearing temperature influences flavivirus vector competence of mosquitoes

Culex annulirostris Skuse mosquitoes (Brisbane strain) were reared at 20 degrees C or 27 degrees C and the adult females were experimentally infected by feeding Murray Valley encephalitis virus (MVE). They were then maintained (a) in the insectary at 20 degrees C, after rearing at either 20 degrees C or 27 degrees C; (b) at ambient outdoor temperatures, range 12.2-28.9 degrees C, mean 19.6 degrees C; or (c) at 27 degrees C after rearing at 27 degrees C. There was no significant difference in rates of MVE infection or transmission when mosquitoes were reared and maintained constantly at 20 degrees C or 27 degrees C. However, for females kept at reduced temperature (i.e. mean = 19.6 degrees C or 20 degrees C after rearing at 27 degrees C), the infection and transmission rates of MVE were significantly reduced (2 x 8 replicates). This investigation illustrates that vector competence is depressed by decreasing temperatures for adult mosquitoes compared with those they experienced during development. Similar patterns were evident with previously published work on Japanese and St Louis encephalitis, dengue and yellow fever. The process appears to be reversible, i.e. increased temperature raises virus infection and transmission rates. It is concluded that, without incubation at warmer temperatures, flavivirus recovery from overwintering mosquitoes will be negatively biased.     

Climate and natural production of rubber (Hevea brasiliensis) in Xishuangbanna,southern part of Yunnan province,China

According to the author's and his collaborators' investigations, the climate influences the growth of rubber trees (Hevea brasiliensis) in Xishuangbanna, the southern part of Yunnan Province, China, in at least four aspects: (1) The yield of latex per tapping and the final yield of dry rubber per tree per year or per unit area per year; (2) the growth rate, as expressed by increment of girth in cm; (3) the survival during the over-wintering period; (4) the initiation or suppression of certain diseases; In this paper the author would like to describe the influence of climatic elements on yield of latex and on survival during the over-wintering period. As for the other two aspects, only general comments are given.     

Seasonal changes of glycogen/trehalose contents,supercooling points and survival rate in mature larvae of the overwintering soybean pod borer Leguminivora glycinivorella

The mature larvae of the soybean pod borer Leguminivora glycinivorella, spend over 9 months (October-next August) in the inactive state until pupation down to 3 cm below the surface in soil. Trehalose content of inactive larvae increases in early winter, attaining a maximum (ca 30 mg/g), and decreases in spring, with a concomitant decrease and increase of glycogen. The median supercooling points seasonally change from ?19.8°C (October) to ?25.0°C (February), and to ?17.0°C (June). The lower supercooling points in winter are in part due to the absence of unusually high values (> ?18°C). The increase in trehalose does not seem to be effective in depressing the supercooling points. The larvae are freeze-intolerant, but ambient temperatures in outdoor conditions are always above the supercooling points. The survival rates are very high throughout the inactive period.     

Bi- and trivoltine complex life cycles in a Kanto (Japan) population of a wild bruchid Kytorhinus sharpianus

The partial trivoltinism and overwintering of Kytorhinus sharpianus Bridwell (Coleoptera: Bruchidae) was studied in the Kanto district, Japan. The later in the summer eggs were laid by the first-generation adults, the higher was the incidence of larval diapause in the second generation. The incidence of diapause also fluctuated between years, influencing the abundance of third-generation larvae. A relatively large proportion of third-generation larvae did not attain the diapause stage by the beginning of winter. The diapause development of larvae in diapause was completed by mid-January. Immature larvae of the third generation also overwintered and emerged as adults in the spring.     

Sporulation ofEnteromorpha spp. (Chlorophyta) and overwintering of spores in sediments of the Wadden Sea,Island Sylt,North Sea

For the last two decades dense mats of species of the filamentous green algaeEnteromorpha spp. have regulary occurred on tidal flats of Köningshafen Bay (island Sylt, North Sea, FRG). In calm areas overwintering of adult plants or plant fragments is a common process to guarantee the mass development during the next season. In contrast, the distribution ofEnteromorpha on exposed sandy tidal flats depends on recruitment by juvenile stages. In 1993Enteromorpha spore settlement was recorded regularly in the field. Polyethylene dishes were placed in the field and left for a period of seven days and lateron cultivated in the laboratory to checkEnteromorpha germling development. During summer 1993 — at a minimum distance of 200 m to the nearest adultEnteromorpha populations — a total of at least 82×10⁶ spores m^–2 settled. During winter the number of spores attached to the collecting dishes was close to zero and the adjacent sand flats were free of any visibleEnteromorpha plants. In further experiments it was shown that the development ofEnteromorpha juveniles in the next spring depended on the overwintering capacity of spores. More than 2×10⁶ spores m^–2 attached to large sand grains and other substrata (e.g. Hydrobia ulvae) survived the winter. In a laboratory experiment several species ofEnteromorpha were able to survive in total darkness for at least 10 months.     

Evaluation of the risk of overwintering Helicoverpa spp. pupae under irrigated summer crops in south-eastern Australia and the potential for area-wide management

Surveys were undertaken to determine the distribution of overwintering pupae of two species of Helicoverpa in south‐eastern Australia. The results indicate that significant populations of H. armigera have the potential to overwinter as pupae in the region under residues of their summer crop hosts. H. punctigera, conversely, was found not to overwinter in the region to any significant degree. The results also suggest that a high proportion of the overwintering H. armigera population are located in relatively few high risk fields. The overwintering population represents an ideal opportunity for control on an area‐wide basis using post harvest cultivation or “pupae busting”. The risk of overwintering H. armigera pupae occurring was largely associated with crop type, the mechanism being related to the date that the crop flowers, the level of pupal parasitism and the use of larval control measures. The results are discussed in terms of recommendations for farmers and it is suggested that a concerted effort to cultivate high risk fields has the potential to significantly reduce the population on an area‐wide basis.     

Seasonal variation in growth, mortality and fat stores of roach and perch in Lough Neagh, Northern Ireland

The annual cycle for roach ( Rutilus rutilus ) and perch ( Perca fluviatilis ) in Lough Neagh, Northern Ireland can be divided into warm 'growing' and cold 'non-growing' seasons. Summer water temperatures declined between 1991–1993, as did the sizes of 0+ fish of both species. Small overwinter increases in length occurred after poor summers due, in roach, to size-selective mortality. Fat content was size-dependent and increased over the summer in both species. All sizes of roach but only small perch lost fat overwinter. Dead roach collected towards the end of the 1992/3 winter had significantly less fat than live individuals. The allocation of energy to growth (and ultimately reproduction) and to fat (and overwinter survival) was modelled as a tradeoff, assuming that fat has twice the energy density of protein and using observed summer and winter changes in body composition. The predicted allocation optima were close to observed values but, for roach, this entailed a substantial survivorship cost.     

Overwintering of Trichogramma ostriniae (Hymenoptera: Trichogrammatidae) within target and non-target host eggs

Trichogramma ostriniae was imported into the USA from China and it continues to be evaluated as a biological control agent against the European corn borer and other lepidopteran pest species. A natural enemy's ability to overwinter is a facet of its biology with important ramifications for biological control and non-target effects. Thus, studies were conducted to examine the ability of the introduced egg parasitoid to survive over winters in central New York State. Eggs of Ostrinia nubilalis, Ephestia kuehniella, Trichoplusia ni, Helicoverpa zea and Utetheisa ornatrix were subjected to parasitism by adult T. ostriniae and then placed out of doors and exposed to winter conditions. For trials initiated in 2003 and 2004, the adult parental wasps were exposed to a diapause-inducing photoperiod and temperature regime in the laboratory; in 2010, parental wasps were conditioned out of doors and prior to the onset of winter conditions. Emergence of their progeny was monitored over time by taking aliquots of parasitised eggs, and holding them under warm conditions until emergence was complete. The level of wasp emergence generally displayed a decline followed by gradual increase until spring. Levels of overwintering ranged from 1% for O. nubilalis to 76% for E. kuehniella, and logistic regression indicated that the odds of overwintering was dependent on the year, host species, time out of doors and varied over exposure time depending on host. The potential to overwinter in New York was further confirmed by positive identification of T. ostriniae from naturally occurring O. nubilalis eggs collected from field sites where augmentative releases had been made in previous years.     

Parental and hybrid Daphnia from the D. longispina complex: long‐term dynamics in genetic structure and significance of overwintering modes

In recent decades, hybridization has become a focus of attention because of its role in evolutionary processes. However, little is known about changes in genetic structure within and between parental species and hybrids over time. Here, we studied processes of genetic change in parental species and hybrids from the Daphnia longispina complex (Crustacea, Cladocera) over a period of six years across ten habitats. These cyclical parthenogens respond to fluctuating environments by switching from asexual to sexual reproduction. Importantly, sexually produced diapausing eggs, which resist extreme conditions such as low temperatures and serve as dispersal stages, are produced to a lower extent by hybrids. Long‐term microsatellite data revealed clear differences between hybrids and parental species. In hybrids, clonal diversity values were lower, whereas heterozygosity and linkage disequilibrium values were higher compared to parental species. Clonal diversity of hybrids responded to the strength of the winter, with cold winters resulting in few genotypes in the following spring. In time windows when only asexual hybrid females survive, priority effects will favour the establishment of the hybrid offspring before hatchlings from parental diapause eggs can enter the community. The constant high levels of heterozygosity maintained by clonal reproduction in hybrids might lead to their successful establishment over time, when they are able to escape competition from both parental species. Although we found evidence that hybrids diversity depends on fluctuating environments, a direct link between hybrid abundance and the strength of winter was missing. Because of reduced adaptability in clonally reproducing hybrids, multiple factors must contribute to promoting their long‐term success in fluctuating environments.     

Preliminary analysis of geographical distribution based on cold hardiness for Evergestis extimalis (Scopoli) (Lepidoptera: Pyralidae) on Qinghai–Tibet Plateau

Evergestis extimalis  (Scopoli) is a pest insect present in spring rape fields of the Qinghai–Tibet plateau. A survey of its distribution and analysis of its physiological and biochemical variances of its overwintering larvae were conducted in this study. Prior to 2006, Evergestis extimalis Scopli appeared only sporadically at the east agricultural district of Qinghai Province at 2,100 m elevation; after 2006, there have been frequent outbreaks at 2,200 m or so height. The insect's distribution has extended continuously toward higher altitudes yearly, and the scope of its damage reached 2,800 m height in 2010. These changes indicate that the cold hardiness of E. extimalis is on the rise. Physiological and biochemical analyses were performed for the insect's overwintering larvae from November 2011 to March 2012. The supercooling point (SCP) and freezing point (FP) ranged from ?6.85°C to ?12.49°C and from ?6.23°C to ?8.17°C, respectively, and both were at their respective lowest points in January 2012; the lowest points of water and fat contents (which did not vary to any extreme degree throughout the test period) were also observed in January 2012. Glycogen content varied from 2.42 mg/g to 4.56 mg/g. Protein content increased gradually at the first two months and reached its peak in January 2012 before dropping slightly. The activity of protective enzymes POD, CAT, and SOD varied with changes in environmental temperature, and each was at its lowest point in January 2012. With the exception of protein and glycerol content, other physiological and biochemical variances were generally parallel with environmental temperature, strongly indicating that E. extimalis has indeed developed cold hardiness.