The complete cDNA sequences of heat shock protein 90 (hsp90) and of heat shock cognate protein 70 (hsc70) were cloned by reverse transcription polymerase chain reaction from the rice stem borer, Chilo suppressalis Walker. They potentially encode a 717-amino-acids (hsp90) and a 652-amino-acids (hsc70) protein, with calculated molecular weight of 82.5 and 71.3 kDa, respectively. The deduced amino acid sequence of hsp90 showed the highest homology of 97.2% to Spodoptera frugiperda hsp90. The closest match of C. suppressalis hsc70 was with Manduca sexta hsc70 at 98.0% identity. Expression of hsp90 in diapausing larvae was higher than that in non-diapausing larvae. No such up-regulation in diapausing larvae was observed for hsc70. In non-diapausing larvae, but not in diapausing ones, hsp90 expression was up-regulated by cold acclimation. Hsc70 expression slightly decreased during cold acclimation irrespective of the state of diapause. Involvement of hsp90 and hsc70 in larval diapause and cold tolerance acquisition in C. suppressalis is discussed.
Overwintering larvae of the rice stem borer, Chilo suppressalis accumulate glycerol and are freezing tolerant to about -25°C. However, non-diapausing larvae cannot accumulate glycerol and are killed by freezing. We compared the extent of tissue damage, the effects of glycerol concentration, and the transport of glycerol and water in fat body tissues from these larvae at selected freezing temperatures. Tissues from overwintering larvae, but not non-diapausing larvae, survive when frozen at -20°C with 0.25M glycerol, but the protection afforded by glycerol is offset by the water-channel inhibitor mercuric chloride. Glycerol in higher concentration (0.75M) affords some protection even to the fat body of non-diapausing larvae. Radiotracer assays of overwintering larvae show that water leaves the tissues during freezing while glycerol enters, and that mercuric chloride disrupts this process. Transport is also disrupted after lethal freezing at -35°C. Therefore, membrane transport of water and glycerol is involved in the avoidance of freezing injury to fat body cells of the rice stem borer, apparently by mediating the replacement of water with glycerol in freezing-tolerant tissues.
SUMMARYCold hardiness of the freshwater apple snail, Pomacea canaliculata, varies seasonally. We investigated lethal factors and physiological changes arising from exposure of P. canaliculata to low temperatures. Snails did not survive freezing. The supercooling point of cold-acclimated (cold tolerant) snails (-6.6±0.8°C) did not differ significantly from that of non-acclimated ones (-7.1±1.5°C) under laboratory conditions. Furthermore, snails died even under more moderately low temperatures approaching 0°C. These results indicate that indirect chilling injury is a factor in the death of P. canaliculata at low temperatures. Regardless of whether the snails were acclimated to low temperatures, all of the dead, and even some of the snails still alive at 0°C, had injured mantles, indicating that the mantle may be the organ most susceptible to the effects of low temperatures. The concentration of glucose in the posterior chamber of the kidney and concentration of glycerol in the digestive gland were significantly higher in cold-acclimated snails than in non-acclimated ones, suggesting carbohydrate metabolic pathways are altered in snails during cold acclimation.
We investigated the effects of temperature and photoperiod on development and oviposition of Frankliniella occidentalis. Even though the developmental periods of eggs, larvae and pupae were shorter at 20°C than at 15°C, no significant difference in the developmental periods was observed between long photoperiod (16L:8D) and short photoperiod (10L:14D). The longevity of adult females was longer under short photoperiod than long photoperiod at 15°C. Fewer eggs were laid per female per day under short photoperiod than long photoperiod at 15°C, but no significant difference in the total number of eggs was observed between the two photoperiods. Furthermore, average pre-oviposition periods under short photoperiod were similar to those under long photoperiod at the same temperatures and adult females continuously oviposited at 15°C under both photoperiods. These results indicate that the F. occidentalis tested undergoes no reproductive diapause under short photoperiod.
Summary
Pomacea canaliculata and P. maculata are invasive freshwater snails originating from South America. The limits of the distributions of the two snails in East and South‐East Asia differ. This study verified a role of cold tolerance in range expansion of the snails and the significance of hybridisation between the two species by comparing overwintering ability and cold tolerance among P. canaliculata, P. maculata and their hybrids.
Field observations, laboratory tests and chemical analyses of glucose and glycerol contents in the snails’ organs demonstrated that P. maculata cannot colonise temperate regions because it lacks adequate cold tolerance.
The hybrids between P. maculata and P. canaliculata exhibited intermediate cold tolerance that is reflected in their current intermediate distribution between the two species in the invaded areas. This indicates a risk of further spread of the hybrid snails into the temperate regions of the invaded area.
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