Survival and Lt50 after exposures at constant low temperature were compared to the values obtained at alternating temperatures in two active (summer acclimated) temperate terrestrial arthropods. The experimental regimes used interruptions - daily transfers from the lower temperature to various higher temperatures for two hours or to one high temperature for Various durations. In both species the alternating conditions improved survival, implying reparation of the chill injury. In the collembolan Orchesella cincta, there was a maximum Lt50 when the higher exposure temperature was equal to the temperature of rearing (19°C). In the bug Pyrrhocoris apterus, Lt50 increased strongly with increasing higher temperature from 0 to 15°C, and was subsequently constant over the entire physiological range suitable for development (to 35°C). Exposure at 0°C was harmful if continuously applied, but survival increased, relative to a constant exposure at -5°C, if the temperature alternated between -5 and 0°C., Zdeněk Hanč, Oldřich Nedvěd, and Lit
Winter climate determines the success of the two main reproductive strategies employed by aphids. Permanent parthenogens survive as parthenogenetic females in mild winters, but are regularly eliminated by low temperatures; while cyclical parthenogens, which switch to sexual reproduction by the end of summer, produce every year fertilised diapausing eggs resistant to frost.
We have studied the variation in sexual morph production of several clones of the cereal aphid Rhopalosiphum padi (L.) showing both strategies. Twenty clones of this species differing by their geographic origin and their mode of reproduction were placed in two laboratory environments mimicking the changes of photoperiod and thermoperiod occurring naturally from the end of summer and during the autumn in oceanic and continental conditions. The analysis of clonal responses in both climatic conditions showed (i) a wide variation in investment of clones in sexual reproduction with, in particular, evidence for a mixed strategy employed by clones producing both sexuals without ceasing parthenogenetic reproduction, (ii) no geographic adaptation among clones belonging to cyclical parthenogenetic populations, (iii) an earlier production of sexuals in continental conditions and a higher production of males in oceanic conditions.
Furthermore, we have compared the dates of first appearance of sexuals in our experiments with those occurring in the field based on a suction trap database and found that sexuals were caught in nature at least four weeks earlier than in the lab. These results underline the need for a better understanding of the influence of the whole array of environmental factors inducing the transition from parthenogenetic to sexual reproduction in aphids., Maurice Hullé, Damien Maurice, Claude Rispe, Jean-Christophe Simon, and Lit
Cold hardiness of larvae of the summer fruit tortrix moth, Adoxophyes orana (Fischer von Rosslerstamm) (Lepidoptera: Tortricidae) was examined in the laboratory. Supercooling point of field collected larvae increased significantly from a mean value of -23.9°C in February 1998 to -16.9°C in June 1998. Mean supercooling points for laboratory diapause and non-diapause larvae were -20.7°C and -17.2°C respectively. Short period of acclimation (10 days at 0°C) significantly decreased supercooling point to -24.7°C for laboratory diapause larvae. Acclimation for 12 days at 5°C decreased supercooling point to -19.4°C for non-diapause larvae. Pre-freeze mortality for diapause and non-diapause larvae was also studied. Constant exposure of diapause larvae at -5°C resulted in high mortality (63.1%) after a period of 30 days. in contrast, only 6 days at -5°C were sufficient to cause 100% mortality of non-diapause larvae. Mortality of non-diapause larvae reached 100% after 12 and 18 days at 0 and 5°C respectively. The importance of these findings for the overwintering strategy of A. orana is discussed., Panagiotis G. Milonas, Mathilde Savopoulou-Soultani, and Lit
We investigated the physiological adaptations for winter survival in a freeze-intolerant chrysomelid, Aulacophora nigripennis, in warm-temperate regions. The adults showed a decreased supercooling point (SCP), increased chill tolerance and high myo-inositol content during winter. Chill tolerance at 0°C appears to be a more suitable indicator of their cold hardiness than SCP because they die at 0°C without freezing and normally an not exposed to subzero temperatures below their SCP., Masahiko Watanabe, Kazuhiro Tanaka, and Lit
Mean development rates under cycling temperature regimes (both alternating and sinusoidal regimes) have been found to be either accelerated, decelerated or unaffected when compared to development at constant temperature regimes with equivalent means. It is generally accepted that this phenomenon is a consequence of the non-linearity inherent in the temperature-rate relationship of insect development and is known as the rate summation, or Kaufmann, effect. Some researchers invoke an additional physiological mechanism or specific adaptation to cycling temperatures resulting in a genuine alteration of development rate. Differences in development rates at constant and cycling temperatures may have important implications for degree-day (linear) population models, which are used in bath pest management and ecological studies.
Larvae of Aglais urticae L. (small tortoiseshell), Inachis io L. (peacock), Polygonia c-album L. (comma) and Vanessa atalanta L. (red admiral) (Lepidoptera: Nymphalidae) were reared at constant (10, 15, 20, 25, 30°C) and alternating (20/10, 25/15, 30/10, 30/20°C) regimes. Development rates under the alternating regimes used were found to differ from those under equivalent constant temperatures in a pattern suggestive of the Kaufmann effect: in all species development at 20/10°C was faster than at 15°C, and for three species development at 30/20°C was slower than at 25°C. The exception was A. urticae. A similar pattern was found for growth rate and pupal weight. The results are discussed with respect to cycling temperature theory and degree-day modelling., Simon R. Bryant, Jeffrey S. Bale, Chris D. Thomas, and Lit
Emp-AKH is a member of the large adipokinetic hormone (AKH) family of peptides. This peptide family appears to occur in the corpora cardiaca of all insect species and its members are involved in regulating substrate mobilisation. The secondary structure of Emp-AKH has been studied in the presence of sodium dodecyl sulfate micelles by comparing data obtained from Nuclear Magnetic Resonance and molecular dynamics simulations. The lowest energy conformer obtained in this study has a turn consisting of residues 5-8 and a tail consisting of the first five residues., Igor Z. Zubrzycki, Gerd Gäde, and Lit
The efficiency of Monte-Carlo procedures to test some hypotheses about the spatial patterns of larvae and damages of Lobesia botrana was studied. Two hypotheses were tested to detect spatial heterogeneity and spatial dependence. The most practical implication is to provide an efficient sampling scheme. The study of the relationship between spatial patterns and grape availability was required to explain scales of spatial heterogeneity and population dynamics studies were needed to relate it to oviposition behavior. It was tested through a third hypothesis. We adapted Monte-Carlo simulation procedures for the analysis of exhaustive count data obtained from regular grids delimited within each of two vineyards. Statistical analyses were based on count permutations and on count redistributions according to the hypotheses which were tested. Indices of aggregation and autocorrelation statistics were used. The hypotheses that we tested at different scales were random distribution of the infestations (HR), independence of vine stock (or groups of k vine stocks) infestation (HI) and independence between vine stock infestation and grape availability (HG). Monte-Carlo tests revealed the same spatial patterns for larvae and damages. We detected different spatial patterns. The implications for sampling were that sample unit could be an individual stock and that sampling along a row could not be used to estimate population density in the vineyard. Results showed that infestation of a given stock depended on grape availability on this stock and on neighboring vine stocks., Isabelle Badenhausser, Patrice Lecharpentier, Lionel Delbac, Pascale Pracros, and Lit
Strong tolerance of freezing is an important strategy for insects living in extremely cold regions. They produce highly effective cryoprotectant systems consisting of ice-nucleating proteins and polyols, which enables tolerable freezing of the body fluid. Therefore, the measurement of the concentrations of polyols and the activity of ice nucleators in the haemolymph is an essential tool for describing tolerance to ice formation in insects occurring in particularly cold places. This study evaluates three parameters: insect body supercooling point (SCP), haemolymph glycerol content and the profile of haemolymph ice nucleating activity that characterize the strategies of cold adaptation and cold hardiness in two previously unstudied beetles, Chrysolina graminis graminis L. and Galerucella nymphaea L., inhabiting Yakutia (Russian Far East, latitude 62°N). The high SCP values, ice nucleating activity and survival of the chrysomelids after freezing indicate that both species are tolerant of freezing. According to the profiles of ice-nucleating activity, the haemolymph from C. graminis graminis is characterized by a higher nucleating potential than that from G. nymphaea. The glycerol level is also higher in C. graminis graminis. The results indicate that both species develop tolerance to low temperatures, but the cold hardiness potential of C. graminis graminis is greater than that of G. nymphaea. This was revealed by the survival test, in which beetles were frozen to a temperature of -22°C for 30 min; 86% of C. graminis graminis and 72% of G. nymphaea survived the test. Thus, the freeze-tolerance of these beetles seems to be based on the production of an integrated cryoprotectant system, the quality of which apparently influences the range of their cold resistance., Natalia G. Li., and Obsahuje bibliografii
Insect herbivores were collected from Castanopsis acuminatissima (Fagaceae) at Wau, Papua New Guinea, by beating the foliage of 15 trees during four one-month sampling periods, each representing different leaf-flush events. The association of leaf-chewing beetles with C. acuminatissima was verified with feeding trials. Of 59 species of leaf-chewing beetles that were collected, 36 species could be used in feeding trials. Only 9 of these species fed on C. acuminatissima. A further 27 beetle species were tested in feeding trials but did not feed. Of these, 7 were specialists feeding on other tree species within the surrounding vegetation. Most beetle species collected from C. acuminatissima foliage were probably transient species, dispersing from other tree species. Path analyses showed that herbivore abundance during a particular sampling period was significantly influenced by rainfall, leaf flush of other conspecific trees and air temperature, but not so by the species richness of surrounding vegetation, number of surrounding conspecific trees and size (DBH) of trees sampled. The species richness of leaf-chewing beetles collected on particular study trees depended on that of the surrounding vegetation, thus supporting the hypothesis that most beetle species collected were transient. The abundance of insect herbivores on particular C. acuminatissima trees probably depends on a balance between the leaf flush of conspecific trees and that of the particular tree sampled. The results also emphasize the need to remove transient species in analyses of insect faunas of tropical trees, at the risk of analyzing species richness patterns derived from loosely defined "assemblages" of species., Yves Basset, and Lit