Seasonal Flight Phenology of Native and Exotic Scolytinae
Initial flight, measured by cumulative degree days (DD), was not affected by year (χ2 = 0.29; df = 1; P = 0.5891) or stand type (χ2 = 3.77; df = 1; P = 0.0522), but was affected by site (χ2 = 16.46; df = 2; P = 0.0003) and species (χ2 = 485.72; df = 26; P < 0.0001; Table 2). Native species had a later average initial flight at 273 DD compared to only 188 DD for exotic species (P < 0.05). One of the earliest beetles to begin flying in spring was X. germanus at 41.1 DD, but with slightly earlier initial flight each year; mid-May in 2014 and 2015 and the last week of April in 2016 and 2019, respectively (Fig. 2), corresponding to a slight increase in degree days each year. Interestingly, A. maiche and X. crassiusculus were later flyers. X. crassiusculus typically began flying mid- to late-May (Fig. 3), around 423.5 DD (Table 2), but the variability was relatively high due to some location-years having low overall captures. A. maiche initial flight occurred consistently within the first week of June (Fig. 4) or 309.9 DD (Table 2).
Flight duration was affected by year (χ2 = 4.41; df = 1; P = 0.0357), site (χ2 = 41.01; df = 2; P < 0.0001) and species (χ2 = 628.31; df = 26; P < 0.0001; Table 2), but not by stand type (χ2 = 0.59; df = 1; P = 0.4418). Exotic Scolytinae species had an average fight duration of 49 d compared to only 10 d flight duration for native beetles (P < 0.05). Anisandrus sayi and X. politus had the longest flight duration for native species at 55.4 and 33.3 d respectively. In comparison, exotic species X. germanus had the longest flight duration of 167.8 d, followed by X. saxesenii at 86.2 d and A. maiche at 81.5 d (P < 0.05; Table 2).
Peak flight of native species occurred around 40‒170 DD with a smaller, secondary peak around 690‒790 DD (Fig. 5A). Generally, two flight peaks were observed for X. germanus–late April to late May or 50–360 DD and then a smaller peak in mid-July or 680–970 DD (Fig. 5B). X. crassiusculus peak flight is difficult to pin-point because overall numbers were quite low in 2014 and 2015, but the largest flight peak was 550–710 DD and smaller peaks occurred as early as 120 DD and as late as 1250 DD (Fig. 5C; Fig. 3). Captures of X. crassiusculus in 2016 were much higher and a peak can be clearly observed at the end of June. In comparison, peak flight occurs in mid-August in 2019, but this could be explained by a warmer spring in 2016 compared to 2019. Peak flight duration of A. maiche was much longer – from approximately 250–1100 DD (Fig. 5D), occurring mid-July in 2014, but with two peak flights observed in 2015 and 2016, from mid- or late-June and again in the first week of August. An earlier peak flight was observed in 2019 during the last week in June, with no large second peak (Fig. 4).
Abundance of Native vs. Exotic Scolytinae
Of the 145,882 total Scolytinae beetles captured across the four trapping years, 622 (0.43%) were native beetles, which was significantly fewer than the 145,260 (99.57%) exotic beetles captured (χ2 = 12489; df = 1; P < 0.0001). There were ~ 340x more cumulative exotic species captured per trap each year (138.1 beetles) than native beetles (0.4 beetles; P < 0.05). Within each year, significantly more exotic vs. native cumulative beetles were caught in both the coniferous (χ2 = 4383; df = 1; P < 0.0001) and deciduous habitats (χ2 = 8216; df = 1; P < 0.0001; Fig. 6).
Total beetles captured per year was significantly affected by year (χ2 = 4.6; df = 1; P = 0.0325), site (χ2 = 25.5; df = 2; P < 0.0001), beetle species (χ2 = 7325.1; df = 26; P < 0.0001), but not by stand type (χ2 = 0.1; df = 1; P = 0.8152). Considering just coniferous woodlots, total beetle captures were affected by year (χ2 = 6.28; df = 1; P = 0.0122), site (χ2 = 17.98; df = 2; P = 0.0001) and species (χ2 = 2252; df = 26; P < 0.0001; Table 2). In deciduous woodlots, beetle captures were not affected by year (χ2 = 0.6; df = 1; P = 0.4386), but were affected site (χ2 = 12.7; df = 2; P = 0.0018) and species (χ2 = 5885; df = 26; P < 0.0001; Table 2). Of the total native beetles collected, 61.1% were captured in coniferous woodlots compared to 38.9% captured in deciduous woodlots (χ2 = 4.053; df = 1; P = 0.0441). Notably, the native bark beetles Cnesinus strigicollis, Conophthorus coniperda, Ips grandicollis, Micracis suturalis, and Pityogenes hopkinsi, and the native ambrosia beetle Gnathotrichus materiarius, were only captured in the coniferous woodlots (Table 2). In contrast, the native ambrosia beetles Anisandrus obesus, Monarthrum fasciatum, Xyleborus pubescens and the exotic bark beetle Hylastes opacus were only captured in the deciduous woodlots (Table 2). Of the total exotic beetles collected, 40.6% were captured in the coniferous woodlots compared to 59.4% in the deciduous woodlots (χ2 = 2.18; df = 1; P = 0.1402).
Overall flight patterns of all native ambrosia beetle species combined showed low numbers of captured beetles, typically under 1 beetle per day with one peak of almost 4 beetles per day (Fig. 5A). The two most abundant native species in both coniferous and deciduous woodlots (P < 0.05), Xyleborinus politus and Anisandrus sayi, represented 3.0 and 1.9 cumulative individuals captured per trap per year, respectively; whereas, the two most abundant exotic species in the coniferous and deciduous habitats, X. germanus and A. maiche, represented 1347.8 and 132.2 cumulative individuals per trap per year, respectively. X. germanus had significantly higher cumulative captures per site per year than any other Scolytinae species in either deciduous or coniferous woodlots (P < 0.0001); with up to 238 beetles per day (Fig. 5B). Across the four trapping years, X. germanus represented a mean of 82.8% and 82.4% of the cumulative beetle captures in the coniferous and deciduous woodlots, respectively (Fig. 6) but were inconsistently higher in deciduous and coniferous woodlots across years (Fig. 2). Number of captured X. crassiusculus were up to 59 beetles per day with similar captures in coniferous and deciduous woodlots, albeit, with very low overall numbers, in 2014 and 2015 and slightly more captures in deciduous woodlots in 2016 and in coniferous woodlots in 2019. It is notable that the Metz location captured zero X. crassiusculus in 2014, 0.25 beetles per trap in 2015 (and much later in the season) and up to just 1 beetle per trap in 2016, then 20 beetles per trap in 2019. However, these numbers were similar in both the coniferous and deciduous Metz woodlots indicating X. crassiusculus likely was introduced into this area sometime between around 2015 and was initially slow to increase in population. Anisandrus maiche represented a mean of 14.6% and 14.3% of the cumulative beetle captures in the coniferous and deciduous woodlots, respectively (Fig. 6). Deciduous woodlots yielded slightly higher captures of A. maiche, with a few exceptions in 2015 and 2019 (Table 2; Fig. 4).
Scolytinae Community Diversity
Over the course of the study, 16 native species and 11 exotic species of Scolytinae were captured (Table 2). Eight of the 27 species were bark beetles of which seven species were native and one species (Hylastes opacus E.) was exotic (Table 2). Of the 19 species of ambrosia beetles, nine were native and 10 were exotic (Table 2).
No significant difference was detected in the total number of native vs. exotic Scolytinae species collected in the coniferous habitats within each trapping year (i.e., 2014, 2015, 2016, 2019; P > 0.05); however, significantly more exotic vs. native species were collected in the coniferous habitats when pooled across the four sampling years (χ2 = 4.72; df = 1; P = 0.03; Table 3). Significantly more exotic than native Scolytinae were collected in the deciduous habitats in 2015 (χ2 = 6.85; df = 1; P = 0.01) and 2019 (χ2 = 7.16; df = 1; P = 0.01), but not 2014 (χ2 = 3.31; df = 1; P = 0.07) and 2016 (χ2 = 1.81; df = 1; P = 0.18); significantly more exotic vs. native species were collected in the deciduous habitats when pooled across the four years (χ2 = 17.23; df = 1; P < 0.001; Table 3). No significant difference in Shannon’s Index (H) or Evenness (Eh) was detected between the coniferous and deciduous habitats within each of the four sampling years or when pooled across years (P > 0.05; Table 3).
Table 3
Species diversity of Scolytinae captured within coniferous and deciduous woodlots in Ohio, USA
|
|
Mean (± SE)
|
Year
|
Stand Type
|
Total No.
Native
Scolytinae Species
|
Total No.
Exotic
Scolytinae Species
|
Statisticsa
χ2; P
|
Shannon’s Index (H)
|
Statisticsb
χ2; P
|
Evenness (Eh)
|
Statisticsb
χ2; P
|
2014
|
Conif.
|
3.0
|
± 0.6a
|
6.0
|
± 1.0a
|
3.06; 0.08
|
0.68
|
± 0.06a
|
0.41; 0.52
|
0.32
|
± 0.04a
|
0.15; 0.70
|
2014
|
Decid.
|
2.7
|
± 0.3a
|
5.7
|
± 0.7a
|
3.31; 0.07
|
0.59
|
± 0.16a
|
0.29
|
± 0.09a
|
2015
|
Conif.
|
3.3
|
± 0.7a
|
7.0
|
± 0.6b
|
3.99; 0.05
|
0.54
|
± 0.14a
|
0.04; 0.85
|
0.23
|
± 0.06a
|
0.00; 0.99
|
2015
|
Decid.
|
2.7
|
± 0.9a
|
7.7
|
± 0.9b
|
6.85; 0.01
|
0.51
|
± 0.15a
|
0.23
|
± 0.08a
|
2016
|
Conif.
|
8.3
|
± 1.5a
|
8.0
|
± 0.6a
|
0.02; 0.89
|
0.44
|
± 0.04a
|
2.11; 0.15
|
0.16
|
± 0.02a
|
1.96; 0.16
|
2016
|
Decid.
|
6.0
|
± 1.0a
|
9.0
|
± 0.0a
|
1.81; 0.18
|
0.58
|
± 0.11a
|
0.22
|
± 0.04a
|
2019
|
Conif.
|
5.0
|
± 1.2a
|
7.3
|
± 0.3a
|
1.33; 0.25
|
0.36
|
± 0.09a
|
2.68; 0.10
|
0.15
|
± 0.04a
|
2.58; 0.11
|
2019
|
Decid.
|
2.7
|
± 0.7a
|
7.7
|
± 0.7b
|
7.16; 0.01
|
0.50
|
± 0.02a
|
0.21
|
± 0.02a
|
Pooled
|
Conif.
|
4.9
|
± 1.0a
|
7.1
|
± 0.6b
|
4.72; 0.03
|
0.51
|
± 0.08a
|
0.31; 0.58
|
0.21
|
± 0.04a
|
0.37; 0.54
|
Pooled
|
Decid.
|
3.5
|
± 0.7a
|
7.5
|
± 0.6b
|
17.23; <0.001
|
0.55
|
± 0.11a
|
0.24
|
± 0.06a
|
a Different lowercase letters within years and rows indicate significant differences in total number of native vs. exotic Scolytinae species using a general linear model and lsmeans (⍺ = 0.05; df = 1).
b Different lowercase letters within years and columns indicate significant differences in Shannon’s index and evenness separately using a general linear model and lsmeans (⍺ = 0.05; df = 1).
|