Implementation and assessment of the classical biological control program against the huanglongbing vector, Trioza erytreae, in the Canary islands

Abstract

The African citrus psyllid Trioza erytreae (Del Guercio) (Hemiptera: Triozidae) is one of the most threatening pests for Mediterranean citriculture. It vectors the phloem-limited bacteria Candidatus liberibacter spp, the causal agent of huanglongbing (HLB), the most devastating citrus disease worldwide. Although HLB has yet to be recorded in Europe, T. erytreae has established in the Macaronesia Islands of Madeira (Portugal) and the Canary Islands (Spain), and in mainland Europe. In 2017, a classical biological control program was implemented, and Tamarixia dryi (Waterston) (Hymenoptera: Eulophidae) was released in an experimental citrus orchard in the Canarian Island of Tenerife in the spring of 2018. This study aimed to analyze i) the distribution and spatio-temporal dispersion of T. dryi, ii) the seasonal trend of T. erytreae and parasitism rates of T. dryi in the field and iii) the effect of T. dryi on T. erytreae population densities in the Canary Islands three consecutive years after the release of the parasitoid. Our results showed that T. dryi successfully established in the island of Tenerife and dispersed in four out of five surrounding islands where T. erytreae was present. Two years after the release of T. dryi, the proportion of sites infested by the psyllid decreased from more than 80% to less than 5% in the three main islands: Tenerife, La Palma, and Gran Canaria. Furthermore, the population density of T. erytreae was extremely low in the sites where it was present two and three years after the release of T. dryi. Parasitism rates remained higher than 40% throughout the sampling periods. Overall, our three-year study shows that the parasitoid T. dryi reduced and controlled the Candidatus liberibacter spp vector, the causal agent of HLB, T. erytreae in the Canary Islands.