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

Abstract

The Walnut Twig Beetle (WTB), Pityophthorus juglandis Blackman, is a small bark beetle native to Mexico and Southwestern USA recorded for the first time in Europe (NE Italy) in 2013. WTB attacks walnut (Juglans spp.) and wingnut trees (Pterocarya spp.) and is the vector of Geosmithia morbida Kolarík et al., a pathogen causing the thousand cankers disease (TCD). WTB and TCD represent a serious threat for walnut orchards in Europe. Spatiotemporal data of the WTB-TCD infestations recorded from an 8-year-long (2013–2020) monitoring conducted in 106 walnut orchards of NE Italy were used to develop a model in order to analyze: (i) the effective dispersal capacity of WTB, (ii) the factors affecting dispersal and (iii) the colonization risk of healthy walnut orchards. We registered a mean annual dispersal of 9.4 km, with peaks of about 40 km. Pest dispersal is affected by distance of suitable hosts from the nearest infested site, number of walnut orchards in the surroundings (both infested and healthy), orchard size and walnut species in the orchard. Using the model, it was also possible to calculate the colonization risk of a specific walnut orchard according to its characteristics showing, for instance, that a medium-size (5,000 trees) black walnut orchard located at 25 km from the nearest infested orchard has an infestation risk of about 50% of probability.

Thousand Cankers Disease in Walnut Trees in Europe: Current Status and Management

“…Its flight capacity is not very high; in fact, one-third of the individuals of the same population were estimated to fly less than 100 m [ 26 ]. Thus, the dispersal of the beetle is mainly sustained by human-mediated transport, as demonstrated in Italy, where a mean annual dispersal of 9.4 km was recorded [ 27 ]. The WTB preferentially attacks stressed trees; however, it can also exploit healthy ones [ 11 ].…”

Enhancement of Boring Vibrations Based on Cascaded Dual-Domain Features Extraction for Insect Pest Agrilus planipennis Monitoring

“…The constant increase in the volume of goods shipped internationally has caused an impressive number of non-native species introductions worldwide [5]. Wood-boring beetles, such as bark and ambrosia beetles (Scolytinae), longhorn beetles (Cerambycidae), and jewel beetles (Buprestidae), are one of the most successful guilds of alien species invasive to forest habitats [6]. Hidden within wood-packaging materials, round wood logs, and live plants, these beetle larvae are often moved both throughout their native biogeographic region and among continents.…”

The spread of Carpophilus truncatus is on the razor's edge between an outbreak and a pest invasion

“…To identify the possible areas of origin for the spreading of the population of sap beetle in Campania, a Geographic Profiling (GP) approach was used [66][67][68] . Although several GP algorithms include the presence of a buffer area, we used the Dragnet algorithm that excludes a buffer zone, because the dispersal capabilities of small coleopterans are rather limited 67,69,70 and the spreading of small coleopteran pests is often more dependent on human activities than dispersal capabilities of the species 71 , but see exceptions 72,73 . To gain a more robust prediction, we used a bootstrap approach 74 by repeating the Dragnet algorithm on 30 subsamples of the whole dataset, with each subsample including a random amount of the original data ranging between 25 and 75%.…”