OVIPOSITION STRATEGIES OF GALL-MAKING SPE CIES OF THE SAWFLY GENERA PONTANIA, EUURA AND PHYLLOCOLPA (HYMENOPTERA, TENTHREDINIDAE, NEMATINAE)

The galling habit within the Tenthredinidae has evolved especially in three genera of the subfamily Nematinae: Pontania Costa 1859, the leaf lamina gallers, Euura Newman 1837, the leaf midrip-, petiole-, bud-, and stem-gallers, and Phyllocolpa Benson 1960, the leaf folders. The o viposition behavior of these gall-making sawflies on willows (Salix Li nnaeus 1754) shows a stereotyped search pattern for oviposition sites. The females [FF] use their antennae and oviposition sheath in searchi ng the suitable willow species. They continuously palpated older and y ounger leaves with their antennae or touched the leaf surface with the oviposition sheath, probably obtaining either tactile or olfactory in formations. Pontania FF form closed galls, which are attached to the m idrip or subsidiary veins of the leaf. They oviposit into developing w illow leaves in spring. FB can oviposit more than once into the same l eaf, and each oviposition causes a gall, containing just one larva. Po ntania species make different gall types: paired, elongated sausage-sh aped galls produced on the upper surface of the leaf blade, bean- or k idney-shaped galls transected by the leaf blade, and pea-shaped galls on the underside of the leaf. The larvae leave the gall and pupate in the soil in late summer. Euura form bud- (subgenus Gemmura Smith 1968) , petiole-, midrip-, and stem-galls (subgenus Euura). The FF of bud-ga lling sawflies oviposit never into vegetative buds but only into new f lower buds (= catkins) for the next year, arising in the axils of youn g leaves. During summer, the larvae develop inside the galls produced within the bud scales by rampant growing of the meristematical tissue so that galled buds usually look bigger than ungalled ones. Fully grow n galls are often covered by a thin layer of silky or woolly hairs, th e existence of which in galled buds of some willow species can be comp letely reduced. The larvae often emerge in late autumn, spin cocoons a nd overwinter on the ground between litter. In some species they pupat e within the gall, often cutting holes in the bud scale and cleaning t he gall room from woolly hairs. The FF of petiole-galling Euura ovipos it into petioles, or as midrip-gallers, into midrips of unfolded new l eaves. The last instar larvae leave the galls and pupate in the soil i n late autumn. The F of stem-galling sawflies probes into the bundle o f unfolded new leaves several times before she oviposits through the n ewly emerging leaves. She inserts her long, saw-like ovipositor into t he young top of the stem. Larvae develop and make cocoons inside the g alls. In some species the last instar larva cuts an exit hole in the g all in late summer, allowing unimpeded emergence of the adult in the f ollowing spring. Phyllocolpa species cause open leaf folds down the ed ge of willow leaves, resulting from induced swelling of the young leaf or retarded longitudinal growth on the roll side through numerous rep eated ovipositor insertions into the leave blade. The egg is laid into the tissue on the edge of the leaf blade or near the midvein. Young l arvae feed within the fold, late instar ones supplementary on the edge of the leaf. In some species only one margin is galled but in other s pecies the leaf rolls are paired and the whole leaf becomes spirally t wisted throughout its length. Pupation of all species is in the soil.