In recent years, the poplar industry has seen rapid growth, particularly in fast-growing poplar species. Planting forestation in the fall or spring requires more time and attention, especially when it comes to preventing and controlling sprouts. Early spring is a critical period, as drought conditions often lead to an increase in pests that can cause significant damage to young poplar shoots. Among these, the black cashmere beetle, the large gray elephant beetle, and the Mongolian longhorn beetle are particularly destructive.
The black cashmere beetle belongs to the scarab family. It has one generation per year, with adults spending winter in the soil. By early April, the adults emerge, initially feeding on early-sprouting weeds before spreading further. From late April to late May, this pest reaches its peak activity period. Adult beetles are nocturnal, remaining hidden in soil crevices during the day and showing phototaxis. Eggs are laid in mid-May at depths of 16-20 cm, and larvae hatch in mid-June. By early August, older larvae burrow deeper into the soil, making cocoons. The pupal stage lasts about ten days, after which new adults remain underground.
The large gray elephant beetle, also a type of weevil, completes two generations annually. These beetles overwinter as both adults and larvae in the soil. They emerge in mid-to-late April and feed on seedlings, laying eggs on leaves in late May. Larvae hatch in early June. By late September, larvae prepare their winter nests. The next spring, they continue feeding until mid-June before emerging as adults in mid-July. The entire lifecycle, from egg to adult, takes two years, with adults unable to fly and relying on crawling movement. At the start of April, they hide in soil crevices or under plant debris. Rainfall can cause some adults to perish due to mud sticking. These beetles are active mostly in the early morning and evening, with females laying around 702 eggs on average. Larvae feed on humus and fine roots in loose topsoil, causing minimal harm to seedlings.
The Mongolian longhorn beetle, another coleopteran, also has two generations annually. Both adults and larvae overwinter. Adults emerge in mid-April, often appearing in the morning or evening. During the day, they hide under clods of soil or near the base of seedlings. The larval stage is most severe from mid-April to mid-May, with over 50 insects found on a single small seedling. Adults lay eggs in the topsoil, and new larvae emerge in late May. Adult beetles reappear in early September. New adults do not emerge from the soil but overwinter in their original nests until April of the following year.
For pest control, several strategies can be employed. Light traps can be used during the adult stage. When pest populations are dense, spraying solutions such as 6000 times dilution of nematocide, 1000 times dilution of 80% trichlorfon emulsion, or 1500 times dilution of 50% carbamate oil can be effective. Seedlings can be treated with poisoned soil using 15 kg of 3% carbofuran granules mixed with 450 kg of fine soil. Root irrigation with 50% phoxim or 80% dichlorvos at 2000 times dilution is another method. Additionally, placing plastic bags over the roots of seedlings not only protects them from pests but also helps retain moisture and promotes growth.
The author's affiliation is with the Forestry Bureau of Kangping County.
This text highlights the importance of understanding and managing these pests to ensure successful afforestation efforts. Each pest presents unique challenges, requiring tailored approaches to minimize damage and maximize survival rates of young poplar trees.
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