a1_Quantitative behavioural traits associated with egg-laying, such as the level of selectivity for host-supports and the size of egg clutches, are generally thought to be of great importance for the subsequent survival and development of offspring. These quantitative traits, however, are often difficult to assess reliably by direct observation in the field. This is particularly the case when the insects are very tiny, which is the case for most galling and leaf mining insects. However, a new approach, the "Melba" procedure, allows the indirect inference of these quantitative traits, using easily recorded field-data only. Application of this diagnostic procedure to a large series of samples of beech leaves (Fagus silvatica), harbouring either a leaf miner, Phyllonorycter maestingella (Lepidoptera: Gracillariidae) or one or the other of two galling insects, Mikiola fagi or Hartigiola annulipes (Diptera: Cecidomyiidae) indicates that the leaf miner differs significantly from the two species of galling insect in term of combined values of host-acceptance ratio and average clutch-size, while the two gall-inducing species remain substantially undistinguishable from each other according to these traits. Thus, the galling insects (i) show stronger selectivity for a host than does the miner at any given average clutch-size and (ii) show larger average clutch-size at any given level of selectivity. That is, for at least these three species, the galling insects show a greater level of selectivity when choosing leaves to oviposit on but, then, tend to lay larger egg-clutches. These differences may be due (i) to the gall-inducing process requiring far more of leaf tissues than being simply palatable, which makes it likely that galling species will be more selective in their choice of leaves than leaf miners and (ii) to the capacity of galls to become nutrient sinks, which may help explain why the galling insects laid larger, a2_egg clutches. However, whether these trends can be regarded as general rather specific to this particular case, depends on the outcome of future studies on other groups of insects with similar life histories., and Jean BÉGUINOT.
It is expected that environmental conditions impact the distribution of galls on host plants. Moreover, insects may induce their galls randomly or choose certain parts of a host to induce such growths. This study aimed to determine whether or not the gall midge, Hartigiola annulipes (Diptera: Cecidomyiidae), which induces galls on leaves of the European beech (Fagus sylvatica), prefers leaves facing a particular cardinal direction. In addition, we wanted to ascertain whether the galls are evenly spread across three leaf zones: proximal, median and distal, distinguished by dividing leaf area along the midrib. The results show that H. annulipes chose leaves facing various directions in different studied locations, and leaf choice is not restricted to the specific leaf area, a parameter that accurately reflects the light conditions of leaf growth. Moreover, the medial leaf zone was preferred, while the distal zone was avoided. The choice of the leaf zone modified the distance between the mid-rib and a gall. Gall distribution in the crown of trees is probably random, while at the leaf level, it is determined by leaf morphology., Sebastian Pilichowski, Marian J. Giertych., and Obsahuje bibliografii