The distribution and management of two invasive pests of Eucalyptus: the red gum lerp psyllid, Glycaspis brimblecombei (Hemiptera: Psylloidae), and the blue gum chalcid wasp, Leptocybe invasa (Hymenoptera: Eulophidae), in Zimbabwe

摘要

Eucalyptus species are indigenous to Australia but arenowgrown worldwide due to their fast growth rate and various uses as timber and fuel wood. Insect pests of Eucalyptus have since followed their host and, in most cases, leaving behind the natural enemies which usually regulate them below economic injury. This is the case with Glycaspis brimblecombei and Leptocybe invasa which are now resident in most parts of the world including Zimbabwe. Damage as a result of the two pests currently poses a threat to reforestation efforts to provide alternative sources of firewood for curing tobacco. The objective of this study was to determine the distribution of the two pests as well as assess the possibility of managing L. invasa through biological control by releasing and recovering successive generations of the natural enemy Selitrichodes neseri in selected L. invasa-infested areas. Surveys were therefore carried out in Zimbabwe and GPS coordinates for pest presence recorded and used to determine the current distribution and future projections of the two pests using Maximum Entropy (maxent) ecological niche modelling. In preliminary studies to manage L. invasa, the natural wasp enemy S. neseri was released in Eucalyptus plantations and recovery studies done to establish their perpetuation in the field. Based on temperature and precipitation averages for Zimbabwe, the model predicted widespread distribution of the two pests especially in Mashonaland West, Bulawayo, Harare, Midlands province and parts of Manicaland province. This predicted range was projected to shrink due to climate change by the year 2055. In terms of relative contribution in predicting the distribution of the occurrence data, the three most important variables were mean annual temperature (39 %), mean temperature coolest month (18.3%) and annual moisture index (18 %). The performance of the model was high, with an AUC value of 0.884. Selitrichodes neseri wasps were recovered in infested Eucalyptus samples 4- 6 generations after the initial release, indicating a high possibility of the natural enemy being able to establish in the future. Our findings are therefore important in understanding the current and projected distribution of both L. invasa and G. brimblecombei in Zimbabwe and formulating management measures for the two pests.