The Heterobostrychus aequalis, also known as the "slender powderpost beetle", belongs to the genus Heteropterygium in the family Bostrichidae. It is a wood-boring pest that causes significant damage to timber, bamboo, rattan and their derivatives (including artificial boards, packaging materials, furniture, etc.). It has been listed by China as an entry quarantine pest and a national forestry quarantine pest. It is primarily distributed in tropical and subtropical regions, with hosts predominantly being tropical and subtropical plants.
I. Morphological Characteristics
The adult Heterobostrychus aequalis has a cylindrical body shape and a reddish-brown coloration. Its head is black with fine granular protrusions, the frontal ridge is raised horizontally at the front, and a longitudinal ridge runs along the center of the head's dorsal surface. Its antennae have 10 segments, the anterior margin of the pronotum is concavely arched, and each side has a prominent, tooth-like projection. The elytra feature distinct striations arranged in rows and have a shiny appearance. The larvae are milky white, plump, with wrinkled body walls, consisting of 12 segments. The pupae are 7 to 10 millimeters in length.
II. Biological Characteristics
The Heterobostrychus aequalis is a xylophagous pest that spends almost its entire life inside hosts such as wood, venturing outside only for adult mating and egg-laying. It can produce 2 to 3 generations annually, with mature larvae or adults overwintering inside the host. Overwintering larvae pupate in mid-to-late March of the following year, with the peak eclosion period occurring between late March and late April. The first generation of adults emerges as early as late June to early July, requiring approximately 100 days to complete one generation. Some larvae extend their developmental period and overwinter as mature larvae. The final batch of adults emerges by mid-to-late March, overlapping with the overwintering stage of the third-generation adults. As a result, both larvae and adults of the Heterobostrychus aequalis are present year-round, with adult activity also observed in winter, showing no signs of hibernation.
III. Transmission Pathways
Adult Heterobostrychus aequalis possess moderate flying ability and can spread over short distances by crawling and flight. Long-distance dispersal primarily occurs through human-mediated transport of wood, bamboo, rattan, their derivatives, and related transportation equipment.
IV. Damage
The Heterobostrychus aequalis has a wide range of hosts, exhibits strong boring ability, and is omnivorous. It can damage living trees, timber, and wood products, and can even bore through glass sealant. The boreholes are mostly round. In mild cases, they consist of multiple holes, whereas in severe cases, the holes resemble a honeycomb pattern, leaving only a thin, paper-like shell that breaks upon touch, rendering the wood completely unusable. Most larval tunnels extend longitudinally along the wood, often bending and interweaving. They can reach lengths of up to 30 cm and have a diameter of approximately 6 mm. The tunnels are filled with powder-like excrement and can penetrate to a depth of 5 to 7 cm.
V. Prevention and Control Measures
(I) Strengthen inspections of host plants and wood preferred by the Heterobostrychus aequalis. The 2nd instar larvae infected with the Steinernema carpocapsae A24 strain can be used to control the pest.
(II) Where feasible, wood can be soaked in water for a duration of no less than 1 month.
(III) In the epidemic-affected area, building materials can be soaked in a 5% boron-phenol solution for 40 to 160 minutes for protective treatment, or heated at a temperature of 93°C for 10 to 20 minutes to sterilize infested materials.
(IV) In areas where wooden boxes are stacked and may potentially be exposed to the pest plague, including all items, walls, columns, floors, and roofs within the premises, apply a thorough spray of a 500-fold dilution of dichlorvos every 10 years, repeating three consecutive times.
(V) Wood (including logs and sawn timber) and bamboo should undergo fumigation with methyl bromide or aluminum phosphide. Wood products (including furniture, plywood, etc.) with a thickness of 2 to 3 cm should be heat-treated for at least 2 hours at drying room temperatures of 65 to 67°C with a relative humidity of 80%.
(VI) Wooden packaging boxes, skids, and similar materials infected with the pest should be destroyed.
VI. Methods for Customs Quarantine and Inspection
(I) Surface inspection: Examine the surface of wood, bamboo, rattan, or their products, packaging materials, and transportation vehicles for signs of live insects crawling, dead insects attached, holes, or residues caused by boring. For wood with bark, peel off the bark to examine for the presence of wormholes and debris.
(II) Dissection inspection: (1) Use saws and knives to dissect suspicious wood or wood with wormholes and debris to check for the presence of adult insects, larvae, or pupae. Check for larvae feeding tunnels that run parallel to the grain of the material. These tunnels are often found in multiples, either side-by-side or interwoven, and are typically filled with powder. (2) Determine the condition of rattan materials by assessing their toughness. Damaged rattan becomes less tough and is prone to breaking easily, which helps in identifying wormholes and insect bodies. (3) Perform a tapping inspection on rattan and willow products: spread a layer of white plastic cloth on flat ground, tap the sample to dislodge hidden insects onto the cloth, and then collect them using a brush and finger-shaped tube.
(III) Feeding and observation: Place the discovered larvae along with their damaged host into an insect-rearing container. Keep them at a constant temperature (20 to 30°C) for observation, and proceed with further identification after the adult eclosion.
(Author Affiliation: Tianjin Customs)
Disclaimer：The above content is translated from Chinese version of China Inspection and Quarantine Times. The China Inspection and Quarantine Times version shall prevail.
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