Synergy Between Low Temperature and Dessication in Breaking Gemmule Diapause of Eunapius fragilis (Leidy)

Summary

Gemmules of Eunapius fragilis collected during the fall and kept at 20° C for up to 6 months did not germinate. Freshly collected gemmules, which were dried at 20° C for 7 days and then rehydrated, also exhibited a very low capacity for germination. However, gemmules, stored at 20° C for several months and then dried, showed a much higher level of germination (but usually no more than 50%) after they were returned to pond water. Gemmules, stored at 4–5° C for 4 to 6 weeks, exhibited at most very little germination when they were tested at 20° C. On the other hand, gemmules, which were chilled at 4–5° C for 4 to 6 weeks and then dried for 7 days, underwent rapid and nearly complete germination upon rehydration. These results provide clear evidence for a synergistic effect between low temperature and desiccation in breaking gemmule diapause. It is suggested that in temporary habitats where E. fragilis often survives the dry summer as gemmules, drying may be the primary agent releasing the gemmules from diapause so that they germinate in the fall upon the return of water. A brief exposure of the gemmules to low temperatures before and/or during the dry period may enhance the effect of desiccation.     

Sexual differences in the crucial environmental factors for the timing of postdiapause development in the rice bug Leptocorisa chinensis

Although the regulation of reproductive diapause by environmental factors has been extensively studied in a variety of insect orders, sexual differences in the regulation of diapause are still poorly understood. We examined the effects of environmental factors including photoperiod, temperature and food on the regulation of reproductive diapause in both sexes of the rice bug Leptocorisa chinensis (Dallas) (Hemiptera: Alydidae) in the laboratory and under natural conditions. There was no significant difference in critical daylength (CDL) for diapause induction between the sexes. The CDL corresponded to the daylength in which development of the gonads was suppressed in half the insects caught in the field. Both sexes enter diapause at the same time in successive seasons. In diapause insects, on the other hand, there were sexual differences not only in retention of responsiveness to photoperiod and temperature but also in the food requirement, and these sexual differences lead to different timing of the resumption of reproductive development after overwintering.     

Evolution of reproductive seasonality in bears

• 1 Of the eight species of Ursidae, six are currently at risk of extinction and the remainder face significant risks to their future survival. One of the greatest threats to bears is human‐imposed environmental alteration (e.g. global warming, chemical pollutants, deforestation). An examination of the reproductive biology and phylogeny of the Ursidae reveals reproductive seasonality as a probable adaptation to adverse environmental conditions.
• 2 Seven of the eight extant species exhibit distinct mating and birth seasons, with the most ancient species evolving facultative seasonality as an adaptation to the increasingly seasonal climate of the Pliocene. The remainder of the extant species evolved during the Pleistocene glaciations, under conditions of severe seasonal food restriction. Under these conditions, an obligate mode of seasonality emerged and persists to the present.
• 3 Knowledge of the natural history of seasonal reproduction in the ursids and how it evolved in response to global climatic change provides a context for understanding the ramifications of current environmental change on the reproduction of these important species.

     

Parapause breakage as a key step for the continuous indoor rearing of Philaenus spumarius

The development of an efficient indoor rearing protocol of Philaenus spumarius is a key step for research on the meadow spittlebug, as it could reduce researchers' dependency on the availability and collection of univoltine individuals in the field. Here, we implemented the rearing protocol previously described by inducing females' parapause breakage before mating. This new step enables the completion of the life cycle of P. spumarius (adult to adult) in 149 days, potentially providing three generations per year under laboratory conditions.     

Time of the season: the effect of host photoperiodism on diapause induction in an insect herbivore,Leptinotarsa decemlineata

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Changes in glutathione redox cycle during diapause determination and termination in the bivoltine silkworm,Bombyx moil

To explore whether glutathione regulates diapause determination and termina tion in the bivoltine silkworm Bombyx mori, we monitored the changes in glutathione redox cycle in the ovary of both diapanse and nondiapauseegg producers, as well as those in dia pause eggs incubated at different temperatures. The activity ofthioredoxin reductase （TrxR） was detected in ovaries but not in eggs, while neither ovaries nor eggs showed activity of glutathione peroxidase. A lower reduced glutathione/oxidized glutathione （GSH/GSSG） ratio was observed in the ovary of diapauseegg producers, due to weaker reduction of oxidized glutathione （GSSG） to the reduced glutathione （GSH） catalyzed by glutathione reductase （GR） and TrxR. This indicates an oxidative shift in the glutathione redox cy cle during diapause determination. Compared with the 25℃treated diapause eggs, the 5℃treated diapause eggs showed lower GSH/GSSG ratio, a result of stronger oxidation of GSH catalyzed by thioredoxin peroxidase and weaker reduction of GSSG catalyzed by GR. Our study demonstrated the important regulatory role of glutathione in diapause determination and termination of the bivoltine silkworm.     

Molecular characterization of DnaJ 5 homologs in silkworm Bombyx mori and its expression during egg diapause

A comparison of the cDNA sequences （1 056 bp） of Bombyx mori DnaJ 5 homolog with B. mori genome revealed that unlike in other Hsps, it has an intron of 234 bp. The DnaJ 5 homolog contains 351 amino acids, of which 70 contain the conserved DnaJ domain at the N-terminal end. This homolog orB. mori has all desirable functional domains similar to other insects, and the 13 different DnaJ homologs identified in B. mori genome were distributed on different chromosomes. The expressed sequence tag database analysis of Hsp40 gene expression revealed higher expression in wing disc followed by diapause-induced eggs. Microarray analysis revealed higher expression of DnaJ 5 homolog at 18th h after oviposition in diapause-induced eggs. Further validation of DnaJ 5 expression through qPCR in diapause-induced and nondiapause eggs at different time intervals revealed higher expression in diapause eggs at 18 and 24 h after oviposition, which coincided with the expression of Hsp70 as the Hsp 40 is its co-chaperone. This study thus provides an outline of the genome organization of lisp40 gene, and its role in egg diapause induction in B. mori.     

Development characteristics of the box‐tree moth Cydalima perspectalis and its potential distribution in Europe

The box‐tree moth Cydalima perspectalis (Walker) is an invasive pest causing severe damage to box trees (Buxus spp.). It is native to Japan, Korea and China, but established populations have been recorded in a number of locations across Europe since 2007 and the spread of the insect continues. The developmental investigations suggest that larvae overwinter mainly in their 3rd instar in Europe and that diapause is induced by a day length of about 13.5 h. One and a half to 2 months in the cold are necessary to terminate diapause. Threshold temperatures for development and number of degree‐days to complete a generation are slightly different from those calculated in previous studies in Japan. A bioclimatic (CLIMEX^®) model for C. perspectalis in Europe was developed, based on climate, ecological and developmental parameters from the literature and new field and laboratory studies on diapause termination, thermal requirements and phenology. The model was then validated with actual distribution records and phenology data. The current distribution and life history of C. perspectalis in Europe were consistent with the predicted distribution. The climate model suggests that C. perspectalis is likely to continue its spread across Europe, except for Northern Fenno‐Scandinavia, Northern Scotland and high mountain regions. The northern distribution of C. perspectalis is expected to be limited by a number of degree‐days above the temperature threshold insufficient to complete a generation, whereas its southern range is limited by the absence of a cold period necessary to resume diapause. The model predicts relatively high Ecoclimatic Indices throughout most of Europe, suggesting that the insect has the potential of becoming a pest in most of its predicted range. However, damage is likely to be higher in Southern and Central Europe where the moth is able to complete at least two generations per year.     

Winter feeding leads to a shifted phenology in the browntail moth Euproctis chrysorrhoea on the evergreen strawberry tree Arbutus unedo

• 1 The browntail moth Euproctis chrysorrhoea is a highly polyphagous univoltine forest pest. Although its young larvae usually overwinter in diapause from early autumn to the beginning of spring, winter larval feeding has been reported when this species feeds on the evergreen woody shrub strawberry tree Arbutus unedo.
• 2 The present study investigated life‐history traits of four populations of E. chrysorrhoea feeding on A. unedo, including phenology of the different life stages, larval feeding activity and diapause incidence. By modelling the relationship between larval size and host plant leaf persistence, elevation and mean annual temperature, we also studied larval development in ten populations of this species sampled from a range of geographical locations in Spain, from both A. unedo and deciduous hosts.
• 3 The results obtained revealed that on A. unedo, E. chrysorrhoea phenology has shifted: from October to March, A. unedo larvae doubled their size, whereas, on deciduous Ulmus minor and Quercus faginea, larval size did not change. General linear models demonstrated that such differences were not related to environmental variables. We also found that on A. unedo larval feeding was arrested for 2 months, with this period representing a true diapause.
• 4 The results obtained in the present study suggest that E. chrysorrhoea populations are phenologically adapted to their local host plants, and that the presence of foliage is a key element in the phenological shift reported on A. unedo. These results may have implications with respect to the formation of E. chrysorrhoea host races.