A citizen science method to monitor a polyphagous shot hole borer infestation in Johannesburg's urban forest

Abstract

Citizen science has become a powerful tool for gathering data, and the validity of these data should be tested. The accuracy of a citizen science database used to monitor the polyphagous shothole borer (PSHB) (Euwallacea fornicatus) (Coleoptera: Curculionidae: Scolytinae) infestation in a suburb of the city of Johannesburg was assessed. Out of 785 trees surveyed by the citizen scientists, 157 trees (20%) were selected as a validation data set to confirm the tree identity, tree health status and level of PSHB infestation. A chi-square (χ2) test was performed to examine whether there was a significant agreement between the citizen scientists’ and researcher’s data used for the classification of the tree infestation, tree health status and PSHB infestation holes. A Cohen’s kappa coefficient was calculated to determine the level of agreement between the two different sources of data, for the infested parts (trunk, main branches, and canopy branches) of the trees surveyed and PSHB infestation signs. The two surveys showed no significance difference for classifying tree health status and PSHB infestation holes. There was a high level of agreement between citizen scientists and the researcher ratings for measures of PSHB infestation (kappa values ranging between 0.71 and 0.89) and the level of agreement was significant. In conclusion, citizen science allowed us to obtain a large quantity of data at a low cost that correlated with the researchers’ validation dataset. Citizen science is a useful method for monitoring PSHB in a diverse urban forest in trees that show obvious signs of infestation.