Viral and bacterioplankton dynamics in two lakes with different humic contents.

Viral and bacterioplankton dynamics were investigated, together with the temporal variation of phage-infected bacterioplankton in two oligotrophic lakes, one humic and the other clearwater. Bacterial abundance was significantly higher in the humic lake, while the abundance of virus-like particles (VLP) was significantly higher in the clearwater lake. There were no differences in either the frequency of infected bacterial cells (FIC), or in burst size between the lakes. Because of the higher bacterial abundance in the humic lake, a larger number of bacteria were lyzed in this lake. FIC showed large seasonal changes, varying between 9 and 43%, which covers almost the entire range of previously published data from both lacustrine and marine environments. The temporal changes in VLP abundance and FIC were slow in both the humic and clearwater lakes. The burst size was low in both lakes (average value, nine in each case), probably because of the oligotrophic status of the lakes. The chlorophyll a concentrations were higher and positively correlated with VLP numbers in the clearwater lake, indicating that a significant proportion of the viruses in this lake may be phytoplankton viruses.

Defensive odor emission from larvae of two sawfly species,Pristiphora erichsonii andP. wesmaeli.

The emission of species-specific odors byPristiphora erichsonii andP. wesmaeli is accompanied by a characteristic defensive behavior called "snap bending." When the larvae are disturbed, blends of volatile compounds are emitted from ventral glands. The odor ofP. erichsonii, a colonial species, is composed of bornyl acetate, borneol,trans-pinocarveol, myrtenol, benzaldehyde, and tetradecyl, hexadecyl, and octadecyl acetates, whereas that of the solitaryP. wesmaeli is composed of 3-carene-10-al, linalool, myrtenal, and benzaldehyde. The role of these compounds in the defensive behavior of the larvae is discussed.