Xylosandrus crassiusculus ( Motschulsky, 1866 )

Buhroo, Abdul Ahad, 2024, A taxonomic monograph of subfamily Scolytinae (Coleoptera: Curculionidae) in the Western Himalaya, Zootaxa 5533 (1), pp. 1-82 : 72-76

57. Xylosandrus crassiusculus ( Motschulsky, 1866)

( Figure 71 )

= Phloeotrogus crassiusculus Motschulsky, 1866

= semiopacus Eichhoff, 1878b ( Xyleborus )

= semigranosus Blandford, 1896b ( Xyleborus )

= bengalensis Stebbing, 1908 ( Dryocoetes )

= mascarenus Hagedorn, 1908 ( Xyleborus )

= ebriosus Niisima, 1909 ( Xyleborus )

= okoumeensis Schedl, 1935 ( Xyleborus )

This species is diagnosed by the following morphological characters: ♀ frons weakly convex with a distinct median line, surface coarsely granulate, a few distinct carinulae on either side of median line converging towards epistomal margin; vertex finely reticulate punctate; vestiture of long, sparse hairs on frons, denser on epistomal margin; eyes elongately oval, rather deeply emarginate; antennal club obliquely truncate on anterior face (type 1); pronotum as long as wide, rounded (type 1) from dorsal view and basic (type 0) from lateral view; anterior margin narrowly rounded armed with ten asperities; summit feebly marked at middle; anterior two-thirds with small asperities; posterior portion finely reticulate with distinct punctures; vestiture of sparse, long hairs antero-laterally and dense mycangial tuft towards pronotal base; scutellum large, shiny and tongue-shaped; elytra 1.25× as long as pronotum, 1.30× as long as wide; basal margin substraight; lateral sides sub-parallel up to basal two-thirds, broadly rounded posteriorly; postero-lateral margins of elytra distinctly carinate and confluent with interstria 7; disc smooth and shiny; striae not so impressed and marked by small and shallow punctures, each with a microhair; interstriae more than three times as wide as striae with irregular two to three rows of punctures as in striae with fine, semi-recumbent hairs; declivity somewhat convex, gradually sloping, feebly elevated towards sutural apex; surface dull with obsolete strial punctures, rather with confused granules throughout; vestiture of small fine hairs and uniseriate rows of long stout setae; color dark-brown; body length: 2.53–2.55 mm, 2.16× as long as wide.

Male deformed in shape and smaller in size; pronotum without asperities; elytra more gradually arched towards apex.

Material examined: New record: India: 3 ♀ ′s. Himachal Pradesh, Palampur, Tanda (32° 06.141′ N, 076° 32.036′ E, 4008 ft.), A.A. Buhroo, 25.09.2018 ( KUIC) .

Distribution: India: Himachal Pradesh (Palampur); wide distribution range from Oriental region to Japan, Pacific islands to Hawaii, tropical Africa and North America

Hosts: Albizia chinensis ( Fabaceae ) and Grevillea robusta ( Proteaceae ) (new host records). Acrocarpus fraxinifolius ( Fabaceae ), Cryptocarya wightiana ( Lauraceae ), Toona hexandra ( Meliaceae )

Remark: Apart from the five species of Xyleborini mentioned above, there are 17 additional species of this tribe that are found in Uttarakhand, according to the recently released Monograph of Indochinese Xyleborini by Smith et al. (2020), which are given in the comparison Table 1.

......continued on the next page ......continued on the next page

The endemism and distribution of scolytine fauna in the Western Himalaya

Bark and ambrosia beetles spread throughout the world’s forests around 120 million years ago, when vast distances of ocean separated most of the continents ( Kirejtshuk et al. 2009). Furthermore, as indicated by periodic radiation bursts, geographic isolation had a significant role in the diversification of species ( Jordal & Cognato 2012). These beetle adults and larvae consume plant tissues such as twigs, branches, trunks, roots, xylem, piths, fruits, and cones. Bark beetles act as the primary decomposers of this plant tissue, which is typically dead or dying ( Stokland et al. 2012). They also provide channels for other decomposers to enter the wood.

The previous studies on the diversity of bark beetles in the northwestern Himalayan region remain fragmentary (e.g., Schedl 1957; Buhroo & Lakatos 2007, 2011; Maiti & Saha 2009; Buhroo et al. 2020; Buhroo & Knížek 2020). To verify the accuracy of the identification and build taxonomic keys, the specimens in the current study were compared and verified with all known Palaearctic and Oriental species that were gathered from different locations throughout the region and at FRI Dehradun. There are 165 species of Scolytinae known to exist in the Himalaya, according to current research and reliable literature ( Knížek 2011; Beaver & Liu 2018; Smith et al. 2020; Beaver & Smith 2022; Knížek & Tshering 2024). The Western Himalayan region yielded 74 scolytine species in the current study, including five new species ( Table 1), while 122 species exist in the Eastern Himalaya ( Nepal, Sikkim, Darjeeling and Bhutan) including 70 species from Nepal ( Beaver & Liu 2018) and 35 species from Bhutan ( Beaver & Smith 2022; Knížek & Tshering 2024). The following species are exclusive to the Western Himalaya: Pityophthorus cedri , P. chilgoza . Cryphalus fulmineus , C. himalayensis sp. nov., C. mangiferae , Crypturgus beesoni , Sphaerotrypes montanus , Coccotrypes cinnamomi , Dryocoetes asperatus sp. nov., D. brownei , D. himalayensis , D. quadrisulcatus , Taphrorychus betulae , Eidophelus indicus , Ernoporus squamosus sp. nov., Hylesinus macmahoni , Hylurgus indicus , Xylechinus padus , Ips stebbingi , Pityogenes spessivtsevi , Pseudothysanoes kashmirica , Carphoborus costatus , C. zhobi , Polygraphus aterrimus , P. difficilis , P. trenchi , Scolytus kashmirensis , S. major , S. stepheni , Scolytoplatypus daimio , S. denticauda sp. nov., S. kunala , S. minimus , Hypothenemus birmanus , H. ficivorus sp. nov., Amasa eugeniae , Diuncus haberkorni , Euwallacea malloti , Planiculus bicolor , Webbia pabo , Xyleborinus saxesenii , Xyleborus cognatus and Xylosandrus mesuae . The genera Dryocoetiops , Pseudoxylechinus , Pseudohyorrhynchus , Phloeosinus , Ambrosiophilus , Arixyleborus , Cnestus , Leptoxyleborus , Microperus , Scolytomimus , Indocryphalus and Trypodendron are found only in the Eastern Himalayan region.

Both Himalayan regions share the 31 scolytine species mentioned in Table 1. In fact, the newly discovered Ernoporus squamosus sp. nov. marks the first record of this genus on Ficus palmata and Morus alba from the Indian sub-continent. Along with Pseudothysanoes modestus , which has previously been recorded from the Far- Eastern Palaearctic subregion ( Mandelshtam et al. 2007; Knížek 2011), P. kashmirica is just the second species of this genus to be reported from all of Eurasia. The species Sphaerotrypes montanus was only observed on its host in the hilly Pir Panjal range, which has a nearly semi-temperate climate, rather than in the main region of Kashmir. Therefore, it is suggested that its range can be the semi-temperate zone of Northwestern Himalaya including the Pir Panjal range until found from some other localities.

Based on the taxonomic comparison presented above and more recent research ( Smith et al. 2020), it appears that the Eastern Himalayan fauna is similar to that of southern China and Southeast Asia, regions with tropical and subtropical climates. Distribution records also show that the majority of ambrosia beetles are found in the aforementioned Himalayan area. Many of those species are found in tropical forests, with just secondary adaptations to the subtropical, mountain, and temperate climates found in the drier western regions and at higher elevations. However, the fauna of the Western Himalaya is diverse and exhibits endemic nature because of altitudinal variations and different types of climatic circumstances. As a result, there is still much to learn about the biodiversity of Scolytinae from a variety of host plants, and this work offers a baseline for future research on the fauna of the Himalayas.

Acknowledgement

This research work was supported by the Science and Engineering Research Board ( SERB), Govt. of India, New Delhi under project File No. EMR/2015/000888. Special thanks are due to Dr. Roger Beaver and to Dr. Miloš Knížek for helpful comments and timely advice during the progress of the work. Dr. Sarah M. Smith and Dr. Alexander V. Petrov are also thanked for help during the handling of the current monographic work. The services and facilities that Dr. Sudhir Singh has provided at FRI Dehradun are commendable. We truly appreciate Dr. Michael Yu. Mandelshtam for his insightful and helpful critique of the monograph, as well as for helping to reshape it .

Figures

FIGURE 71. Xylosandrus crassiusculus. Female: dorsal view A, lateral view B, frons C.