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Coffee white stem borer (Xylotrechus quadripes) Photo: placeholder pending image-fill pass

Coffee white stem borer (Xylotrechus quadripes)

The white stem borer (WSB), Xylotrechus quadripes Chevrolat (Coleoptera: Cerambycidae), is the single most destructive insect pest of arabica coffee in India and is endemic to South Asia. Larvae tunnel through the main stem of mature arabica bushes, often killing the entire plant; in heavy infestations CCRI Balehonnur has recorded plant mortality of up to 5,000 plants/ha per year in unmanaged blocks. The pest does not attack robusta, which is a key reason for robusta's expansion at lower elevations.

Identification and symptoms

  • Adult beetle: 15-22 mm long, dark with two pale yellow transverse bands across the elytra; active April-June and September-November (twin emergence peaks coinciding with post-monsoon dry spells)
  • Eggs: laid singly in crevices and under loose bark on the lower 60 cm of the main stem
  • Larvae: cream-white, legless, robust, up to 30 mm; tunnel longitudinally through the heartwood
  • Symptoms: irregular wilt and yellowing of leaves on a single primary or the whole bush; ridge-like splits ("scars") down the bark; coarse frass at the base; hollow sound on tapping the stem; on heavy attack the bush snaps off at ground level

Hosts and life cycle

WSB is specific to Coffea arabica. C. canephora (robusta), C. liberica and C. dewevrei are non-hosts. Mature, sun-exposed bushes are most vulnerable; well-shaded blocks with intact two-tier shade (Coffee Shade Cultivation Silver Oak) suffer markedly less damage. The life cycle is univoltine in most of Karnataka, with eggs laid in summer hatching into larvae that tunnel through the winter and emerge as adults the following dry season.

Damage and economic impact

Adult emergence coincides with post-blossom dryness when stems are most exposed. A single larva can kill a 6-10 year-old bush. Coffee Board surveys in Chikmagalur estimate that WSB causes 5-10% annual plant loss in unmanaged arabica blocks and up to 20% mortality during outbreak years, with cumulative loss being the principal reason for shortened arabica replanting cycles in India.

Management

The Coffee Board IPM package centres on prevention rather than chemical cure (which is largely ineffective once larvae are inside the heartwood):

  • Cultural (primary): maintain adequate two-tier shade — shade is the most consistent suppressor of WSB pressure; bark-swabbing the lower 60 cm of stem with lime + lindane substitute (chlorpyriphos 0.05%) before each adult emergence peak; mechanical removal and burning of infested bushes during summer-handpicking operations
  • Mechanical: tracing larvae through frass exit-holes and killing them with a wire-probe in the off-season
  • Resistant interplanting: progressively replacing arabica with robusta or CCRI selections under heavy WSB pressure; CCRI work on partial resistance is ongoing but no commercial fully-resistant arabica is yet released
  • Sanitation: complete uprooting of dead and severely infested bushes by April to prevent adult emergence

See also: Coffee Arabica S 795 Selection, Coffee Arabica Cauvery Catimor, Coffee Arabica Vs Robusta India, Coffee Robusta Cxr Coffea Canephora, Coffee Berry Borer Hypothenemus, Coffee Shade Cultivation Silver Oak.

Sources

  1. White Stem Borer Management - CCRI Balehonnur. Central Coffee Research Institute.
  2. Coffee Board WSB Advisory. Coffee Board of India.