Life cycle, parasitism and damage of Xanthogaleruca luteola (Muller) in Valencia (SE Spain): A preliminary study

Abstract

Xanthogaleruca luteola (Muller) (elm leaf beetle, ELB) (Coleoptera, Chrysomelidae) is a serious pest for elms in urban green areas of Mediterranean climate zones in Spain. In order to design an integrated pest management strategy, a study was conducted on this insect in the city of Valencia (east Spain) in six streets that house trees of the species Ulmus minor. Four larvae increases were found that peaked in mid-May, the first half of July, the second half of August and the end of September/beginning of October. The mean degree-days accumulations required for completion one generation were 612°D±24.98, and 461.12°D±43.95 were needed between the oviposition peaks and adult emergence peaks. Larvae caused a higher degree of defoliation than adults. The defoliation levels caused by generations 1 and 2 were similar, and higher than those caused by generations 3 and 4. Defoliation ranged between 30% and 100% in September. The degree of defoliation and citizen pressure led to treatment, performed by injecting trunks with abamectin in the first generation in three streets under study. This treatment did not allow the level of defoliation to increase with each new generation, and the mean degree of defoliation remained below 30% throughout the study period. Two parasitoid species were identified: Oomyzus gallerucae (Fonscolombe) (Hymenoptera, Eulophidae) from the eggs and Erynniopsis antennata (Rondani) (Diptera, Tachinidae) from larvae, prepupae and pupae of ELB. Nonetheless, during the year of this study, and after considering the defoliation undergone by elms, the parasitism level was low and insufficient to keep Elm leaf beetle at tolerable levels. The integrated ELB management involved regularly monitoring defoliation levels with each new ELB generation by setting the treatment threshold at 20% defoliation and favouring biological control by increasing the quantity and diversity of plants in urban green areas to provide natural enemies with refuges and food.