Response of the subterranean termite Reticulitermes grassei Clement (Isoptera: Rhinotermitidae) to pH of substrate

Reticulitermes grassei Clement is an Iberian subterranean termite whose feeding activity can damage both urban infrastructures and oak forests, becoming a main pest. In consequence, the development of new control methods compatible with the environmental conservation is a priority. Recently, techniques for termite control supported on the fact that the soil pH can be a chief factor in restricting termite populations have been explored. On this basis, we consider the possibility of taking advantage of certain current harmless silvicultural techniques, which also vary the soil pH, to control populations of R. grassei in natural environments. Before addressing this question, it was necessary to know the termite response to pH of substrate. For this instance, this work aimed to establish the range of pH in different zones of R. grassei nests and to determine the tolerance of this species to pH ranges outside of those observed in field. In addition, the effect of termite activity on soil pH is assessed. This research has been carried out from October 2018 to March 2019, in several natural areas from Cordoba (Spain). The results indicate that R. grassei preferably colonizes neutral or somewhat acid substrate, ranging from 5.4-7.5; the pH values in the inner nest increases towards the periphery. In addition, this species shows rather tolerance to alkaline substrate (pH <= 8.5). Nevertheless, it seems to be more sensitive to acid pH, being observed the lowest tolerance limit at pH approximate to 4.5; if pH drops to 4.0, mortality is near 100 %. According to our results, the alkalization of substrate would not be a feasible procedure to control R. grassei populations in forest of southern Iberian Peninsula.