Effect of light and botanical species richness on insect diversity

Composition and diversity of flying insects was assessed within and along one-year-old sown/unsown field margin strips installed along both the shaded and unshaded side of an old lane of beeches. Investigated factors were light regime, plant community and monitoring position. Both insect composition and spatial preference of insect families was strongly dependent on light regime, field margin type and monitoring position. The number of insect families preferring the shaded side was fivefold higher than the number of families preferring the unshaded side. Particularly, insect families associated with moist conditions (Haliplidae, Dolichopodidae, etc.) were preferably or exclusively found on the shaded side characterised by higher soil moisture content. Some families (Bibionidae, Scatopsidae, Proctotrupoidea, etc.) showed higher abundance in the unsown field margin whilst others (Cicadellidae, Chalcidoidea, etc.) preferred the sown field margins. Similarly, some families (Lygaeidae, Cantharidae, etc.) occurred preferably in the field margin strip whilst others (Chironomidae, Empididae, Cicadellidae, etc.) preferred the adjacent field crop. Differential habitat preference might be explained by differences in botanical composition and structure of the vegetation. Insect diversity was significantly higher near the margin strip richest in botanical species (i.e. the unsown margin strip), reflecting the highest Shannon diversity index (2.57). Furthermore, insect diversity was significantly higher on the shaded side, irrespective of monitoring position, with Shannon diversity indices between 2.59 and 2.70