Poplar stem borer (Apriona)
A long-horned beetle grub that tunnels deep into the poplar trunk — the leading insect cause of downgraded logs and standing tree loss in Indian poplar plantations.
- Pest
- Apriona cinerea (long-horned beetle)
- Damages
- Trunk sapwood and heartwood
- Peak activity
- Adult egg-laying June–September
- Main risk
- Downgraded peeler logs; standing tree loss
Overview
Poplar stem borer (Apriona cinerea) is the single most damaging insect on farm-grown poplar across the north-Indian belt of Punjab, Haryana, western Uttar Pradesh and the tarai. The adult is a large greyish-brown long-horned beetle, active in the warm monsoon months (June to September), that lays its eggs in slits it cuts into the bark of a young growing tree. The grub that hatches is pale, thick and up to about 5 cm long by the time it is mature, and spends most of its year-plus life tunnelling upward through the sapwood and heartwood of the trunk.
The clearest field sign is a mound or wet mass of coarse, chewed-out frass pushed out of a bore hole on the bark, usually within the first few metres of the trunk. Fresh sap oozing from the same hole in the growing season is a second warning. Inside, the widening tunnel breaks the peeler-grade continuity of the log — a badly bored tree that would have sold as veneer at felling is downgraded to packing-wood grade or rejected outright at the mill gate, so even a moderate attack in a WIMCO/Trident buy-back block is a real rupee loss. Because the grub feeds hidden inside the trunk, control leans on inspection, physically killing grubs in fresh bore holes, and protecting the trunk during the adult egg-laying window — not calendar sprays.
How to identify it
- A mound or wet mass of coarse, chewed-out frass pushed out of a bore hole on the bark within the first few metres of the trunk.
- Fresh sap oozing from the same hole during the growing season, and a small round exit hole later when the adult beetle emerges.
- The greyish-brown adult long-horned beetle on the trunk or lower branches through the monsoon months.
- On felling, a broad tunnel running up through the sapwood and heartwood that ruins the peeler-grade log — the definitive confirmation.
What causes it and when
- The grub of the long-horned beetle Apriona cinerea, laid by the adult in slits it cuts into the bark of a young growing tree.
- The grub spends more than a year tunnelling upward through the sapwood and heartwood of the trunk before it emerges.
- Adult beetle activity, and therefore fresh egg-laying on the block, peaks in the warm monsoon months (June to September).
- Blocks stressed by water shortage, poor establishment or nearby dead poplar/mulberry stumps carry heavier attack.
Cultural & organic control
- Walk the block every 15–20 days from June to September looking for fresh frass and sap flow on the trunk — this is the only reliable early detection.
- Where a bore hole is found early, insert a stiff wire, a bicycle spoke or a length of clutch cable up the tunnel and rotate it to mechanically kill the grub inside.
- Remove and burn any dead or beyond-recovery poplar tree, plus dead mulberry (Apriona also breeds on mulberry) within and around the block, so they stop breeding fresh beetles.
- Keep the trunk healthy — irrigate young blocks through the first two summers and avoid mechanical wounds — since stressed and injured trees attract more egg-laying.
Chemical control
- Plug each fresh bore hole with a piece of cotton wool soaked in kerosene or in a CIB&RC-registered insecticide such as dichlorvos, then seal the mouth with clay or mud to hold the fumes and kill the grub inside.
- A trunk swab or spray with a recommended contact insecticide (a synthetic pyrethroid or a chlorpyriphos formulation) on the lower 3–4 m of the trunk, timed to June–July when the adults are laying, cuts fresh egg deposition.
- Confirm the currently recommended insecticide, concentration and safe-use precautions for poplar stem borer with your state forest research institute (FRI Dehradun) or the nearest KVK.
- Broad-spectrum calendar spraying of a poplar block is neither necessary nor economic — target detection and the two months of adult activity, not the whole rotation.
Prevent it coming back
- Keep the fortnightly monsoon-window inspection as a fixed routine, every year of the rotation, not just after damage is suspected.
- Remove and destroy dead poplar and mulberry trunks and stumps from around the block promptly, so they stop seeding the next generation of beetles.
- Keep the block well-watered and un-wounded in its first two summers; stressed young trees attract disproportionately heavy egg-laying.
- On a fresh planting, use only healthy ETPs from a WIMCO/PFRI-linked nursery — poor plants stressed at establishment carry attack for the whole rotation.
Crops most at risk
Where this problem is called out in our crop guides — open a crop for the full package of practices.
Frequently asked questions
I see a wet mound of coarse frass on the bark of my poplar tree — is this borer?
Yes — a mound or wet mass of coarse, chewed-out frass pushed out of a bore hole in the trunk is the classic first sign of poplar stem borer (Apriona cinerea). The grub is inside the tunnel behind that frass. Act immediately: probe the hole with a stiff wire or clutch cable to kill the grub mechanically, or plug the hole with kerosene-soaked cotton wool and seal it with clay. Leaving the grub in place for another season lets the tunnel widen and downgrades the log at felling.
Does one bored tree spread the pest to the whole block?
Not directly through the tree, but yes indirectly — the grub takes more than a year inside the trunk, and when the adult beetle emerges through a small round exit hole it flies to fresh young poplar (and mulberry) in and around the block to lay its next generation of eggs. That is why removing and burning dead or beyond-recovery poplar and mulberry trunks promptly matters so much: they are the source of next year's adults.
Will a peeler-grade log survive a light Apriona attack?
Usually not at full peeler value. Peeler grade at a WIMCO/Trident-type mill requires a clean, straight, unblemished bole; even a moderate borer tunnel breaks the veneer-cutting continuity and the log is downgraded to packing-wood grade or rejected at the gate. That is why the fortnightly monsoon inspection and prompt killing of grubs in fresh bore holes pays back so sharply on a buy-back block, even though it looks like a small task.
Symptoms and control measures follow ICAR, KVK and state agricultural-university package-of-practices; any named chemical is a registered use. Always read the product label and confirm the dose for your crop and zone. editorial policy.