Effect of the western conifer seed bug <i>Leptoglossus occidentalis</i>, an invasive alien insect, on seed production reduction in Japanese black pine <i>Pinus thunbergii</i>

To determine the potential reduction of the seed productivity of Japanese black pine (Pinus thunbergii) by the western conifer seed bug (Leptoglossus occidentalis), two feeding experiments were conducted in the center of Kyushu Island, southwestern Japan, in fall of 2020. First, L. occidentalis individuals and a preharvested P. thunbergii cone were enclosed in a nonwoven fabric bag for 2 weeks, which yielded a mean filled seed rate of 18.8% compared with that of 35.6% in the control. Second, L. occidentalis individuals and harvested cones were enclosed in a plastic case for 1 week, affording a mean filled seed rate of 25.7% compared with that of 36.4% in the control. These results suggest that L. occidentalis feeding reduces the filled seed rate of P. thunbergii and damages the seed orchards of this species. Additionally, P. thunbergii seeds from cones damaged by L. occidentalis could be distinguished by their germination ability when sorted using an ethanol floatation technique. Overall, these findings suggest the importance of carefully monitoring L. occidentalis infestation in P. thunbergii seed orchards.</p

Principal component analysis (PCA) plot of eight <i>Myrica gale</i> var. <i>tomentosa</i> populations.

Red arrows indicate the parameters used as variables of soil water chemistry. Black characters indicate the abbreviation of populations in Table 1; Oike: Oike, Po: Po, Ochi: Ochiishi, Bek_C: Bekanbeushi_Center, Bek_E: Bekanabeushi_Edge, Oikan: Oikanamai, Kimon: Kimonto, Benten: Bentennnuma.</p

Summary of chemical analyses of soil water in eight habitats of <i>Myrica gale</i>.

Summary of chemical analyses of soil water in eight habitats of Myrica gale.</p

Transections of leaves of representative <i>Myrica gale</i>.

Transections of leaves of representative Myrica gale.</p

Leaf characteristics.

Leaf characteristics.</p

Summary of habitat characteristics based on concentrations of soil water chemistry using PCA.

Summary of habitat characteristics based on concentrations of soil water chemistry using PCA.</p

Standard partial regression coefficient for LMA and AIC based on the GLMs.

Standard partial regression coefficient for LMA and AIC based on the GLMs.</p

Fig 4 -

Relationship between thickness of palisade layer per mesophyll layer and sexes (a), mesophyll porosity, PC3, and sexes (b), and δ13C values and PC2 (c). The line and shading indicate the mean and the 95% confidence intervals of GLMs. Red circles and lines: females, blue triangles, lines: males.</p

Schematic overview of the relationship between leaf characteristics and habitat environmental conditions.

Schematic overview of the relationship between leaf characteristics and habitat environmental conditions.</p

Mean leaf mass per leaf area (LMA; μg / cm²), thickness of the palisade layer per mesophyll layer (P/M; mm/mm), and δ¹³C (‰) of male and female leaves in eight habitats of <i>Myrica gale</i>.

(DOCX)</p