The cold hardiness of individuals from overwintering populations of a freeze susceptible bug Pyrrhocoris apterus from central and southern Europe differed significantly. Supercooling point (SCP) correlated well with both lethal temperature (LT50) and lethal time (Lt50), and is agood index of cold hardiness of adults during and after diapause. In January, diapause terminated, but cold hardiness was similar to that recorded in November; cold hardiness decreased slightly in March and markedly in May. Short exposure (less than a week) to higher temperatures before termination of diapause did not reduce the cold hardiness. Cold hardiness did not closely follow air temperatures.The Bulgarian bugs retained lower cold hardiness regardless of acclimation to harsh field conditions in the Czech Republic. The interpopulation difference is therefore a heritable character representing an adjustment to local climates.
Ten aphid species wcre used as prey for Adalia bipunctata and six of them (Euceraphis betulae, Cavariella konoi, Liosomaphis berberidis, Acyrthosiphon ignotum, Aphis farinosa and Macrosiphoniella artemisiae) are new essential preys for this coccinellid. Eucallipterus tiliae and E. betulae were the most suitable prey according to the rate of larval development, larval mortality, adult fresh weight and coccinellid abundance in the field. They are followed by L. berberidis, C. konoi and Tuberculatus annulatus. M. artemisiae and A. ignotum are also very profitable food in the laboratory, but they do not occur in the field together with A. bipunctata. A. farinosa from Salix caprea and Aphis fabae from Philadelphus coronarius were not very suitable as food due to the larval mortality (27% and 23%, respectively). A. fabae from Atriplex sagittata was an unsuitable prey: larval mortality was 67% and the adults that emerged as the survivors had the lowest weight recorded in this series of experiments. Aphis spiraephaga was also unsuitable prey: all 1st instar larvae of A. bipunctata died, even though slowly.
One of the factors affecting the effectiveness of predatory coccinellids in an aphid infested crop is the food specificity of the predator. The response towards six species of aphids (Sternorrhyncha: Aphididae) was therefore tested in one of the most abundant aphidophagous coccinellids in Bulgaria - Propylea quatuordecimpunctata (L.) (Coleoptera: Coccinellidae). All aphid species studied (Acyrthosiphon pisum Harris, Aphis craccivora Koch, Eucallipterus tiliae (L.), Euceraphis betulae (L.), Phorodon humuli (Schrank) and Myzus persicae (Sulzer) cultured on transgenic Bt and conventional (non-Bt) potatoes were suitable food according to the rate of larval development, larval mortality and adult fresh weight. Females of P. quatuordecimpunctata fed with M. persicae cultured on Bt potato, or on non-Bt potato or on a mixture of M. persicae from Bt potatoes and A. craccivora, laid a little more eggs than those fed only with A. craccivora.