The Effects of Weather on the Flight of an Invasive Bark Beetle, Pityophthorus juglandis

Abstract

The walnut twig beetle, Pityophthorus juglandis Blackman (Coleoptera: Scolytidae), vectors the fungus Geosmithia morbida, which has been implicated in thousand cankers disease of walnut. Little is known about the flight behavior of the insect across seasons, or about the variability in its flight patterns with weekly fluctuations in weather. We sampled flying adults weekly over a 142-week period (from 29 August, 2011 to 2 June, 2014) with 12-unit black plastic multiple funnel traps baited with a male-produced aggregation pheromone in California, USA. Up to 5000 beetles were captured per trap per week, although catches in most weeks were less than 100 insects. Trap catches were regressed against terms for precipitation, solar radiation, vapor pressure, air temperature, relative humidity, wind speed, and trap catches in preceding weeks. The number of beetles captured in each of the preceding two weeks explained most variation in a current week's catch. This strong temporal autocorrelation was present in regression models developed for males, females, and both sexes pooled. These models were improved by including two environmental variables. Captures of P. juglandis increased with mean weekly air temperature and decreased with increasing mean minimum relative humidity. The percentage of variation in male, female, or total trap catch explained by the temporal variables and the two environmental variables in these multiple regression models ranged from 72% to 76%. While the flight of this invasive insect will likely be affected by site-specific factors as it spreads to new areas, the strong temporal correlation present in this system may provide a useful starting point for developing flight models for newly invaded areas.

Competitive Advantage of Geosmithia morbida in Low-Moisture Wood May Explain Historical Outbreaks of Thousand Cankers Disease and Predict the Future Fate of Juglans nigra Within Its Native Range

“…Nevertheless, wood MC is not the only abiotic factor likely to limit the potential geographic range of G. morbida and P. juglandis in J. nigra (Kolařík et al, 2011;Sitz et al, 2017). Most importantly, climatic differences may impact the flight activity and survival of P. juglandis (Luna et al, 2013;Hefty et al, 2017Hefty et al, , 2018Chen et al, 2020). Within the native range of black walnut, it is also possible that xerophilic and thermotolerant fungi such as Xylariaceae and Aspergillus spp.…”

“…Seybold et al, 2019;Moricca et al, 2020). Moreover, the failure of P. juglandis to successfully establish in the native range of J. nigra despite incidental introductions and high host susceptibility may be due to unfavorable conditions for its symbiont (Utley et al, 2013;Moore et al, 2019), in addition to differences in temperature and seasonal precipitation that may affect beetle flight, dispersal, and survival (Luna et al, 2013;Hefty et al, 2017Hefty et al, , 2018Chen et al, 2020).…”

“…For example, in Tippecanoe Co., Indiana (IN), in the humid midwestern United States, summer MC of J. nigra wood was much higher, at 14.9 ± 0.20% (n = 156) for air-dried lumber and 20.1 ± 0.29% (n = 180) for retail firewood (Williams and Ginzel, unpublished data), the predominant pathway for the movement of invasive woodboring pests (Newton and Fowler, 2009;Jacobi et al, 2012). Furthermore, the peak flight of P. juglandis typically occurs in the spring (Sitz et al, 2017;Chen et al, 2020), coinciding with high levels of precipitation in the Midwest.…”

Dispersal and colonization risk of the Walnut Twig Beetle, Pityophthorus juglandis, in southern Europe

“…Although some of the most important factors affecting WTB presence and its dispersal probability have been clarified (distance from nearest attacked site, attack index, available host index, orchard size and tree species), the role of other variables-such as environmental conditions (e.g., dominant winds) and human-related activities (e.g., main trade routes, volume and type of potentially infected goods)-should be carefully considered to better understand the potential spread of this relatively new invasive pest across Europe and to establish effective containment and local eradication measures. Help in this regard may come from the recent work of Chen et al (2020) presenting the effects of climatic variables (i.e., precipitation, solar radiation, vapor pressure, air temperature, relative humidity and wind speed) on the flight activity of WTB. Considering also the other Italian regions where WTB was found, after its first record in 2013 the insect traveled over 320 km westwards reaching the Piedmont region in 2014 (Bosio and Cooke-McEwen 2018) and about 200 km southwards reaching the Tuscany region in 2018 (Moricca et al 2019).…”

Bark and Wood Boring Insects—Past, Present, and the Future Knowledge We Need

“…The walnut twig beetle, Pityophthorus juglandis is native to the southwestern USA and Mexico but in less than a decade, it has managed to expand northwards to other western and eastern States [ 12 ] and also invade Italy [ 13 ]. As a recent study has shown [ 14 ], P. juglandis captures in pheromone traps increased together with the mean weekly air temperature and decreased as the mean minimum relative humidity increased, evincing a strong dependency on the local temperature and rainfall regime. Indirectly, drought periods manipulate the interaction between carbon allocation and secondary metabolites (a component of plant defense against insects and pathogens) in plants [ 15 ], something that has largely defined the large-scale bark beetle outbreaks which have intensified in the last decades.…”