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 life tables of the aphid predators Coccinella septempunctata L., Ceratomegilla undecimnotata (Schneider) and Propylea quatuordecimpunctata (L.) (Coleoptera: Coccinellidae), fed on Aphis fabae Scopoli (Hemiptera: Aphididae), were constructed at constant conditions (25 ± 1°C, 65 ± 2% RH; 16L : 8D). The average total fecundities of C. septempunctata, C. undecimnotata and P. quatuordecimpunctata were 1996.8, 1160.5, and 724.6 eggs / female, and the average longevities were 94.9, 88.3, and 68.9 days, respectively. The net reproductive rates (Ro) were 1004.1, 544.3, and 375.1 females/female, and the intrinsic rates of increase (rm) 0.118, 0.142 and 0.166 females/female/day, respectively.
The oviposition deterring effects of fresh larval tracks of Cheilomenes sexmaculata (F.), Ceratomegilla undecimnotata (Schneider), Cycloneda limbifer Casey, and Harmonia dimidiata (F.) on C. sexmaculata females were compared in standard laboratory choice tests. Moreover, the persistence of intraspecific effects of C. sexmaculata larval tracks were investigated. Fresh tracks of C. sexmaculata, C. limbifer and C. undecimnotata larvae effectively deterred C. sexmaculata females from ovipositing. The effect of fresh larval tracks of H. dimidiata was not statistically significant. The oviposition-deterring effects of 10 d-old conspecific larval tracks were considerably lower than those of fresh tracks, but remained significant. Clutch sizes were smaller in the blank test without larval tracks than in choice tests with fresh tracks of conspecific, C. limbifer, C. undecimnotata, H. dimidiata larvae and with 10 d-old tracks of conspecific larvae. The study indicates that semiochemicals in the tracks of conspecific and heterospecific coccinellid larvae can contribute considerably to the spacing of C. sexmaculata offspring among prey resources of differing quality and that conspecific as well as heterospecific larval tracks can influence clutch size.
The ability of the aphidophagous coccinellids Cycloneda limbifer Casey and Ceratomegilla undecimnotata (Schneider) to discriminate between simultaneously provided clean paper strips and paper strips with oviposition-deterring larval tracks was studied after the ablation of different sense organs. Females oviposited similar numbers of eggs on paper strips with conspecific tracks and on clean paper strips only when deprived of both maxillary palpi. C. undecimnotata without maxillary palpi also did not differentiate between clean paper strips and paper strips with tracks of the coccinellid Leis dimidiata (F.). If both antennae and one maxillary palpus were simultaneously ablated, females of both species laid significantly more eggs on clean than contaminated paper strips. The results of this study indicate that females use contact chemoreceptors on maxillary palpi exclusively to detect oviposition deterring tracks of conspecific larvae.
Intact females of C. limbifer laid significantly larger batches of eggs on paper strips with conspecific larval tracks, than on clean paper strips in blank test. In contrast, intact females of C. undecimnotata laid significantly smaller batches on paper strips with conspecific tracks than on clean paper strips in blank test. This is the first evidence of an opposite effect of conspecific oviposition deterring larval tracks on egg clustering in aphidophagous coccinellids.
Reflex bleeding is one of the many anti-predation behavioural tactics used by insects. This behaviour is recorded widely in several insect taxa and provides scientists with an interesting opportunity for easily obtaining samples of haemolymph for physiological experiments. However, there is no good evidence that haemolymph and reflex blood have the same characteristics. In this study, we compared three basic characteristics of reflex blood and haemolymph collected from the body cavity, of three species of ladybirds: Harmonia axyridis, Coccinella septempunctata and Ceratomegilla undecimnotata. In the reflex blood we recorded the same concentration of haemocytes and total protein, and level of antimicrobial activity against Escherichia coli as in samples of haemolymph collected from within the body cavity. Therefore, reflex blood is a promising source of haemolymph for use in many physiological and immunological studies. It is the best way of collecting haemolymph if one wants to avoid challenging the immune system and concurrently also enables one to repeatedly collect haemolymph from one individual without injuring it, which would initiate repair mechanisms. The interspecific comparison indicates significant differences among the species studied in three characteristics measured. Interestingly, the native species Ceratomegilla undecimnotata has nearly as effective immune system as the invasive Harmonia axyridis based on the level of antibacterial activity against Escherichia coli.