Studies on the flight capabilities of Pityophthorus juglandis
Pityophthorus juglandis (Coleoptera: Scolytidae) and its associated fungus Geosmithia morbida together cause thousand cankers disease (EPPO A2 List) on walnut (Juglans spp.) and wingnut (Pterocarya spp.). Laboratory studies using flight mills have been conducted in the USA to assess the flight capabilities of P. juglandis. In total, 654 P. juglandis were placed on the flight mills for a 24 h trial period. Results showed that the mean flight distance was 372 m (median distance 158 m), with a maximum flight distance of 3.6 km. During the 24 h trial period, beetles flew on average for 34 min. It was also observed that male and female flight capacities were similar, even though males are larger than females. The age after emergence had no effect on flight distance, flight time, or mean flight velocity. However, the propensity to fly decreased with age. Extrapolations were made (Monte Carlo simulation) and it was estimated that over 5 days (without mortality) only 1% of the insects would fly > 2 km, and that 1/3 of the insects would fly < 100 m. These results suggest that without anthropogenic transport or wind-aided dispersal, the capacity of P. juglandis for natural spread is limited. However, it is stressed that caution should be taken when relating laboratory-based flight potential to natural dispersal.
Sources
Kees AM, Hefty A, Venette RC, Seybold SJ, Aukema BH (2017) Flight capacity of the walnut twig beetle (Coleoptera: Scolytidae) on a laboratory flight mill. Environmental Entomology 46(3), 633-641.