Seasonal damage on stone pine cones and seeds caused by feeding of Leptoglossus occidentalis (Hemiptera: Coreidae)

Western conifer seed bug, Leptoglossus occidentalis, is a cone pest known to cause severe reductions in seed production in its native range in North America. This insect has been introduced and spread all over Europe. Its spread within the Mediterranean region has been coincidental with notable reductions in cone production and yield in stone pine, which raised great concern among forest owners and pine nuts producers.

Several experiments were carried out in a clonal orchard of Pinus pinea located in Tordesillas (Valladolid, Spain) during 2015 and 2016. Pairs of two virgin F1 females, reared in laboratory from wild parents, were caged for two weeks in pine braches, each bearing one 2^nd or 3^rd year cone. Different treatments, consisting in 4 different caging occasions, from late April to late July (3^rd year cones) or late August (2^nd year), were set in 15 trees (blocks) in a complete randomized block design. Exposed cones and caged cones without bugs were also included as control treatments. Similarly, 1^st year conelets were caged with two 2^nd/3^rd instar nymphs for a week in early July and late August. Cones were checked weekly and let to develop once the treatment has ceased. Mature cones were collected in December and were weighted and dried in laboratory. Seeds were extracted, weighted and opened and possible damages were characterized as one of three types.

Preliminary results show that L. occidentalis had a very severe impact on the cones of all ages. All 1^st year conelets receiving feeding during early July died, as did all 2^nd years cones that had bugs during spring or first half of summer. A seasonal effect on cone mortality, seed abortion and seed damage types was observed.