Aspects of the ecology and behaviour of Hylastes ater (Paykull) (Coleoptera: Scolytidae) in second rotation Pinus radiata forests in the central North Island, New Zealand, and options for control

Abstract

This study examined aspects of the pest status and ecology of Hylastes ater in Pinus radiata reforestation sites. Aspects of the flight activity, larval survival and adult emergence from stumps by Hylastes ater and Hylurgus ligniperda were investigated. H .ater was found to be univoltine with a peak of flight activity in autumn. Competition from H. ligniperda has displaced H. ater from sites harvested during the spring and summer months. H ligniperda was bivoltine with peaks of flight activity in spring and summer. The establishment of H. ligniperda in New Zealand has resulted in changes in the lifecycle of H. ater. Attack by Hater on P. radiata seedlings was found to be the dominant cause of seedling mortality in the first year after planting. Although high mortality of seedlings has been recorded from some sites, seedling mortality greater than 10% was found to be uncommon in this study. However, high levels of sub-lethal feeding were common in many plantings. High-risk sites were those harvested in autumn and planted the following winter. Seedlings treated at planting with the insecticide Marshal suSCon® demonstrated a significant reduction in mortality due to Hater attack. Marshal suSCon® had a repellent effect on H. ater. Sub-lethal attack did not effect the growth of seedlings in the first two years after planting. Six species of sapstain fungi were isolated from sub-lethally attacked seedlings. There was a significant relationship between severity of attack and invasion of the seedling by sapstain fungi. A seventh species of sapstain was isolated from H. ater but was not found in any of the experimental seedlings. Because of the potential economic significance of these findings, further research is required to unequivocally demonstrate whether or not H. ater vectors sap stain fungi to seedlings during attacks. Six unrelated P. radiata seedling types were assessed for resistance to Hater attack. Seedling types exhibited varying levels of resistance to attack. The frequency of attack was not different between resistant and non-resistant seedlings, indicating that Hater did not make a selection prior to attack. Further research is required to fully understand the mechanisms of resistance, but opportunities exist for resistant seedlings to be used in management programmes. H. ater and H. ligniperda were attracted to volatiles in the field. Ethanol added to α-pinene, β-pinene and raw turpentine had a synergistic effect by enhancing attraction. Although there were differences in numbers trapped by the different treatments, sex ratios of Hater attracted to volatiles and the control were equal in number. This indicates that aggregation or sex pheromones are not likely to be produced by Hater, and it is attracted to host volatiles. The information generated during this research was used to suggest strategies to manage the risks associated with Hater in second rotation forests in New Zealand.