Pinhole borers in tree crops Kerala

Abstract

The study entitled ‘Pinhole borers in tree crops of Kerala’ was conducted at Department of Entomology, College of Agriculture, Vellayani, during 2022-2024. The main objectives of the study were to assess the distribution of pinhole borers in Kerala and the fungal diversity associated with it. Survey conducted across different districts of Kerala, revealed pinhole borer infestation in tree crops such as coconut (Cocos nucifera L.), arecanut (Areca catechu L.), rubber (Hevea brasiliensis Mull.Arg.), jack (Artocarpus heterophyllus Lam.), rambutan (Nephelium lappaceum Linn.) and teak (Tectona grandis Linn.f.). Maximum number of pinholes was recorded at a height of 100-200 cm of the infected main trunk. Typical symptoms of infestation included yellowing and drooping leaves, gum exudation, and the presence of toothpick-like frass extruded from boreholes. Powdery frass accumulation was also observed around the base of affected trees. The study identified five species of pinhole borers from four genera belonging to the subfamilies Scolytinae and Platypodinae: Xylosandrus crassiusculus (Motschulsky), Xyleborus perforans (Wollaston), Euplatypus parallelus (Fabricius), Euwallacea similis (Ferrari) and Xyleborus sp. The survey recorded 16.60 percentage incidence of X. crassiusculus and Xyleborus sp, in rambootan from Thiruvanthapuram. In coconut, 12 percentage incidence of X. perforans was reported from Malappuram. E. parallelus incidence was reported in arecanut from Thiruvanthapuram () and Kasargode () as well as and rubber in Kannur (). E. similis incidence (16.60-25 %) was recorded in jack from different locations of Thiruvanthapuram. Widespread pinhole borer infestation was observed in rubber plantations in Kannur district, recording the highest incidence (62%). Notably, Xylosandrus crassiusculus was recorded as the first pinhole borer infesting rambutan which is 2.17−2.42 times as long as wide. Posterolateral margins of elytra carinate to interstriae 7. Declivity densely granulate, granules spaced by less than one diameter of a granule. Euplatypus parallelus was recorded from both arecanut and rubber, distinguished by the absence of pores on either side of the i longitudinal sulcus on the pronotum in both sexes, a tri-dentate elytral apex in males, and deeply impressed male elytral striae that are subequal in width to the interstriae at the base of the declivity. Xyleborus perforans, reported from coconut, is identified by its obliquely triangular protibia and declivital interstriae 1 and 3, each armed with 2–3 pairs of moderate tubercles. Euwallacea similis, characterized by its laterally broadened declivital interstriae 1 with a prominent median tubercle and several small granules, is reported for the first time as a pinhole borer in jackfruit. DNA barcodes of Xylosandrus crassiusculus and Euplatypus parallelus were deposited in NCBI (Accession Numbers PQ463778 and PQ463786). The isolation of associated fungal organisms was carried out from the galleries of pinhole borers. The identified species included Fusarium oxysporum from rambutan, Fusarium sp. from jackfruit, Aspergillus sp. from coconut, Penicillium sp. from arecanut, and Trichoderma harzianum from jackfruit. In conclusion, the study identified five species of pinhole borers from four genera belonging to the subfamilies Scolytinae and Platypodinae across various districts of Kerala. Their host plants included rubber, arecanut, rambutan, coconut, and jackfruit. Fusarium oxysporum and a related Fusarium species were associated with Xylosandrus crassiusculus in rambutan and Euwallacea similis in jackfruit, highlighting the diverse fungal associations linked to these borers.