Kermes vermilio Planchon and Nidularia pulvinata (Planchon, 1864) (Hemiptera Kermesidae) outbreaks off urban Quercus ilex L. (Fagaceae)

Abstract

Kermes vermilio and Nidularia pulvinata severe outbreaks are lethal to young holly oaks and strongly damage adult trees. Such infestations are common in several South Italian urban and peri-urban areas and have been reported for a while. Recently we have been observing in Bari (Apulia region) a new considerable invasion of both Nidularia and Kermes on Q. ilex not scale-infested hitherto. The phenomenon is possibly in connection with the new northward expansion of Nidularia that is presently recorded in Italian areas with a continental climate as Veneto and Romagna regions. City surveys and damage estimations revealed the entity of kermesidae impact regarding direct and indirect costs for the maintenance of urban parks, public gardens and leisure areas, avenues and boulevards. Moreover, we discuss the synecology of the two species evaluating the prevalence of mixed infestations on the same plant or the reciprocal competitive displacement. Possible causes of the actual outbreak may lie in ecological disturbance along the rural-urban transition zone, changes in the available range of insecticides, wrong or absent tree maintenance, changes or fluctuation in climatic parameters.

Mixed infestations by Kermes vermilio and Nidularia pulvinata off Quercus ilex are not truly mixed; this is evident as we realise that K. vermilio prefers to infest host twigs while N. pulvinata mostly sets on the trunk and the main branches. The two species seems to share a single host plant occupying two near but distinct niches.

Damages are similar, being both the Kermesidae capable of inducing die back, but Nidularia actively damages the trunk, also.

In a case of infested public greeneries, the officers are usually unable to check the pests, i. e. by an IPM strategy or by chemical control. Possibly because of the extended swarming of crawlers or the missing of effective insecticide authorised for urban area use. Moderate control is given by tree formulate injection but results often less useful than expected. Another phytosanitary “pest cleaning” measure applied by the officers consists of cutting down symptomatic dried twigs as massive pruning every four-five years.

Intense pruning in spring and the consequent plant re-sprouting appears favourable to plant health but for a very short lapse. New sprouts are quickly colonised by wandering crawlers and became intensely infested. Moreover, twigs and small branches cut down leave on the plant much more of the Nidularia population while prune down most of the Kermes out the plant.

Intense and not timed pruning favours Nidularia by displacing Kermes from the host plant in such a way that urban Q. ilex are heavily infested by the most damaging and lethal of the two pest species.

We classified from 1 to 5 the staging of the die back induced by Kermesidae, as reported in table below.