Adults of some coccinellid species overwinter in aggregations consisting of many individuals. They may clump because adults are attracted to particular environmental stimuli and/or of an innate tendency to join conspecific individuals. Aggregation behaviour was studied in Coccinella septempunctata L., which forms small clumps, and Ceratomegilla undecimnotata (Schneider) and Hippodamia variegata (Goeze), which form large clumps. Adults were recorded at five hilltop hibernacula (400-1500 m altitude) in central Europe (50-51°N, 14-16°E) for periods up to 27 years. The hibernacula occur in areas sparsely covered with isolated grass tussocks or completely with stones. Numbers of adults recorded under each of 300-900 stones or among the stems of the grass tussocks were counted every year at each hibernaculum. The degree of aggregation was determined using Taylor's power law. The coccinellid distributions became more aggregated and the size of the aggregations increased as their abundance increased, less in C. septempunctata than in the other two species. Aggregations formed even in the absence of prominent structures, which may attract immigrants, and even when unoccupied stones or tussocks suitable for overwintering were available. Aggregations may be established and their size limited by the strength of the intrinsic preference to join conspecifics. The supposed advantage of aggregated overwintering must be greater than the risk associated with the easy spread of diseases.
The effects of body size on mating success and duration of copulation were investigated in Pyrrhocoris apterus. Under laboratory conditions relative mating success of small and large males was investigated in groups of 2 males (majority sex) : 1 female (minority sex). Large males were recorded significantly more often in copulation than small males when the female was large but not when the female was small. This was also the case when the group size was 24 males : 12 females or population density decreased by increasing the area of the experimental arena. In groups of 2females : 1 male, large females were recorded in copulation significantly more often than small females when the male was large but not when the male was small. Proportion of individuals of the minority sex that copulated was similar for males and females, regardless of body size. The average duration of copulation was similar for small and large males, but shorter for small than large females. The difference in the duration of copulation of small and large females was greater when it was with small rather than large males. The prolonged guarding of large females by small males may be explained by a trade-off between increasing the probability of inseminating an uneasily accessible high quality partner and copulating with more females.
The hypothesis that small species of aphidophagous coccinellids need lower aphid population densities for reproduction than large species (Dixon, 2007) was tested in the field. In 2006 we compared seasonal changes in the oviposition behaviour of two coccinellid species regularly found in cereal stands in central Europe, the large Coccinella septempunctata L. and the small Propylea quatuordecimpunctata (L.). Adults of both species were collected at 2-3 day intervals from stands of winter wheat and spring barley, females were allowed to deposit eggs for 24 h following collection and the percentage that laid eggs and the number of eggs were recorded. Both species colonized the cereal crop simultaneously in the middle of May. After colonization of the crop, while the aphid density was still low, few females of C. septempunctata oviposited and laid only a few eggs. Oviposition increased up to a maximum c. 1 month later and was closely associated with prey abundance. Of the females of P. quatuordecimpunctata, whose mass is about one quarter of that of the former species, the percentage ovipositing and number of eggs laid varied less in time and was less associated with prey abundance than in C. septempunctata. As predicted by theory, the small P. quatuordecimpunctata was more effective at exploiting the lower prey densities as it produced proportionally more of its eggs during the early stages of the aphid infestation than the larger C. septempunctata.
Seeds of many species of plants may survive for a long time in the soil and germinate when brought to the surface, but
whether they are subsequently eaten by seed predators is unknown. We examined the preferences of three species of carabids
(Coleoptera: Carabidae) for 25 species of seeds and determined the difference in palatability between freshly dispersed and those
buried for six years. The stability of their preferences was tested using a collection of seeds of different species, each of which was
offered fresh or after being buried. Carabid beetles readily accepted previously buried seeds as food. In total, Pseudoophonus
rufi pes and Amara littorea ate more fresh seeds than previously buried seeds, while the opposite was true for Harpalus affi nis. The
seeds of some species were even more attractive to carabids after burial than in the fresh state. For all the species of carabids
tested, the diet breadth was similar when the beetles were fed fresh or buried seeds, but the preferences for fresh and buried seed
of particular species were correlated only in P. rufi pes and A. littorea. We measured the seed characteristics (mass and viability)
likely to be associated with the loss of attractiveness to carabids during burial. The change in carabid consumption was not related
to changes in any of these characteristics. This fi nding indicates that factors responsible for variation in seed acceptability are
complex. This study provides the fi rst conclusive evidence that invertebrate seed predators will feed on seeds from seed banks,
although they prefer fresh seeds.
The development stages of a species may have an identical lower development threshold (LDT) and proportionally different durations. This phenomenon called "rate isomorphy" (RI) has been demonstrated for a number of insect species. In contrast, the growing day degrees accumulated over the period of larval development (sum of effective temperatures SET) should be plastic and vary with environment conditions. The prediction from RI is that, with changing conditions, the uniform LDT should be accompanied by differences in development time which remain proportional at different temperatures. This was tested by investigating the effect of diet on thermal requirements for development of larvae of the polyphagous species Autographa gamma (L.) (Lepidoptera: Noctuidae). The larvae were kept at 15.0, 20.3 and 26.7°C and fed on leaves of 13dicotyledoneous herb and tree species. The proportion of total development time spent on a particular diet was plotted against temperature. The existence of RI was inferred from a zero change in development time proportion with changing temperature. This rigorous test supported RI for 3 of 9 diets where development was completed in all temperatures. The LDT observed on 11 diets where the larvae completed development in at least 2 temperatures varied between 9.3 and 11.0°C while SET varied between 167 and 353 day degrees (dd). Assuming RI, LDT and SET for those 9 diets were recalculated. The recalculated LDT was 10.0°C and SET varied between 177-257 dd. The SET increased with decreasing water content and decreasing nitrogen content of food. Worsening food quality decreased food consumption, metabolic and food conversion efficiency, and the relative growth rate of the larvae. Increasing metabolic costs of development were thus positively correlated with SET. The standardized rate of growth (mg.dd-1) was typical for particular diets. Pupal mass decreased with increasing temperature and, within each temperature, with development length.
Development rates of the eggs of 9 species, larvae of 6 species and pupae of 6 species of the genus Amara (Coleoptera: Carabidae) were recorded at five constant temperatures between 17 and 28°C, and thermal constants for each development stage calculated. The lower development threshold varied between 9.2-13.5°C for different stages and species. Rate isomorphy, which implies the existence of a common temperature threshold for all development stages, was demonstrated in 5 species. The sum of effective temperatures differed between stages. On average the egg stage took 18%, the first larval instar 13%, second instar 13%, third instar 35% and pupa 21% of the total development time. A poor diet increased the SET of the larvae. The results are compared with published data on Carabidae.
In central Europe Adalia bipunctata (L.) occurs in two main colour morphs (typical, melanic), and A. decempunctata (L.) occurs in 3 morphs (spotted, chequered, dark). Temporal variation in the relative frequency of morphs was recorded in populations of the Czech Republic where geographic variation in morph frequency is low. Seasonal trends were investigated in samples collected by a light-trap run daily from March to November for 14 years. In A. bipunctata the melanic form was more abundant in autumn than in spring but the difference was not significant. In A. decempunctata morph proportions did not change seasonally. Samples were also collected by sweepnet from stands of many plant species. In both Adalia species the morph proportions did not differ significantly among collections made on different plants. Long-term changes in morph proportions were analysed by pooling annual samples over all host plants. In A. bipunctata, sampled in 15 years between 1971-2004, there was no significant change in proportion of typical (90.1%) and melanic (9.9%) forms. In A. decempunctata, sampled in 12 years between 1976-2004, the proportions of "spotted" (mean over the years 29.4%), "chequered" (42.2%) and "dark" (21.3%) morphs varied between years. There was a trend toward an increasing proportion of the spotted form in the 2000s compared to the 1970s and 1980s.
In 1995-1997, we studied the factors which may influence the ground "activity density" of Carabidae using pitfall traps placed in winter wheat, winter rape and pea stands (1995 only) grown within a 1 km2 area with uniform physical conditions. The traps were placed in plots of bare ground established within the crops and under surrounding intact plant stands. The communities were similar between crops within years (Pearson's correlation coefficient r = 0.60 - 0.81), and between years within crops (r = 0.89 - 0.91), except for the poor winter rape stand in 1997. Factors influencing carabid "activity density" were: (i) Density of crop stand. The carabids preferred crop-shaded ground as long as crop density was low or medium but moved to bare ground plots when crop density became high. Under moderate crop density the preference differed between beetle species, most of which preferred crop-shaded ground while a few ones preferred bare ground. Carabid preferences were probably determined by microclimatic differences caused by presence and density of crop cover. (ii) Presence of seeds dropped on the ground. In rape stands, presence of crop and weed seeds increased the "activity density" of seed predators (species of genera Amara, Harpalus, Ophonus and Pseudoophonus). Scattering of rape seeds significantly increased local activity density of Harpalus affinis and H. distinguendus in the wheat stand. (iii) Presence of aphids. Activity density of Bembidion lampros and Trechus quadristriatus and between-year variation in pooled abundance of the five species recognised as aphid predators was associated with variation in aphid abundance.