Abstract
Seasonal and diurnal flight patterns of the invasive walnut twig beetle, Pityophthorus juglandis, were assessed between 2011 and 2014 in northern California, USA in the context of the effects of ambient temperature, light intensity, wind speed, and barometric pressure. Pityophthorus juglandis generally initiated flight in late January and continued until late November. This seasonal flight could be divided approximately into three phases (emergence: January–March; primary flight: May–July; and secondary flight: September–October). The seasonal flight response to the male-produced aggregation pheromone was consistently female-biased (mean of 58.9% females). Diurnal flight followed a bimodal pattern with a minor peak in mid-morning and a major peak at dusk (76.4% caught between 1800 and 2200 h). The primarily crepuscular flight activity had a Gaussian relationship with ambient temperature and barometric pressure but a negative exponential relationship with increasing light intensity and wind speed. A model selection procedure indicated that the four abiotic factors collectively and interactively governed P. juglandis diurnal flight. For both sexes, flight peaked under the following second-order interactions among the factors when: 1) temperature between was 25 and 30°C and light intensity was less than 2000 lux; 2) temperature was between 25 and 35°C and barometric pressure was between 752 and 762 mba (and declined otherwise); 3) barometric pressure was between 755 and 761 mba and light intensity was less than 2000 lux (and declined otherwise); and 4) temperature was ca. 30°C and wind speed was ca. 2 km/h. Thus, crepuscular flight activity of this insect can be best explained by the coincidence of moderately high temperature, low light intensity, moderate wind speed, and low to moderate barometric pressure. The new knowledge provides physical and temporal guidelines for the application of semiochemical-based control techniques as part of an IPM program for this invasive pest.
Highlights
The invasive walnut twig beetle, Pityophthorus juglandis Blackman (Coleoptera: Scolytidae) [1,2], is native to the southwestern USA and Mexico [3], but it has expanded its range in the USA to include nine western and five eastern states [4,5]
Underscoring the potential international significance of thousand cankers disease (TCD) to the world’s walnut culture, P. juglandis and G. morbida were reported in 2013 in northern Italy, in association with black walnut trees grown in plantations for timber production [8]
Pityophthorus juglandis flew at very low levels in December and January but generally initiated seasonal flight between late January and late February and ceased flight at the end of November (Fig. 1A)
Summary
The invasive walnut twig beetle, Pityophthorus juglandis Blackman (Coleoptera: Scolytidae) [1,2], is native to the southwestern USA and Mexico [3], but it has expanded its range in the USA to include nine western and five eastern states [4,5]. (Ascomycota: Hypocreales) [6] [known collectively as thousand cankers disease (TCD)], the phloeophagous P. juglandis has driven an expanding pattern of mortality of black walnut trees (Juglans spp.) in the western USA [5,7]. Underscoring the potential international significance of TCD to the world’s walnut culture, P. juglandis and G. morbida were reported in 2013 in northern Italy, in association with black walnut trees grown in plantations for timber production [8]
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