Abstract:

Objective: This study examined the correlation between the living habits of a newly recorded pest, the birch leaf miner, in Jilin, and the environment, in order to provide a strategic basis for controlling the dispersal of the pest. Method: A combination method of DNA molecular identification with morphological characteristics was used to clarify the taxonomic status of the insect. The indoor and field comparative observation methods were used to record the habits of the pest and describe various insect stages. A fixed sample survey was performed in the forest to assess the number of mature larvae, cocoons and adult moths in the soil before overwintering. The test plots were artificially watered at 3 days intervals to imitate the average monthly precipitation during the adult moulting season until adult moulting. We measured and recorded the effects of soil water content, soil temperature and soil chemical properties on moulting. Result: The results showed that the insect is Profenusa thomsoni, which was for the first time found to infest birch trees in Jilin. The insect had two generations a year in Jilin, with irregular generations. In early June, the emergence of adult occurred. The larvae were discovered in the lower leaves of birch trees, and the first generation of larvae was observed from late June to early July, during which most of the larvae shed their leaves and fell into the shallow soil layer, while a few of them pupated in the leaves and emerged as adults. From late August to early September, the mature larvae escaped from the leaves into the soil and made soil cocoons mainly in the 5–10 cm layer for overwinter. The first generation of adult pinnipeds started to lay eggs near the birch leaves, and the adults laid 4–6 eggs in a single leaf. The first generation of mature larvae pupated between the upper epidermis and the fence layer of birch leaves or on the soil surface. The second generation of adults migrated to the upper canopy to lay eggs after eclosion. The egg incubation cycle was 10 days and the larvae had 6 instars. In drought years, the eclosion was delayed in the field until rainfall, when the adults were able to successively moult. Through correlation and redundancy analyses between soil physical and chemical properties and adult eclosion in the following year, it was showed that soil water content was the key determinant of the occurrence and amount of birch leafminer pests, and a relatively high soil water content significantly promoted adult eclosion. There was a positive correlation between soil pH, nitrogen content, and eclosion rate, while soil temperature had little impact on adult eclosion after overwintering. The other factors, such as soil total carbon, nitrogen and phosphorus content, posed no impacts on the survival of last instar larvae of the birch leafminer in soil. Conclusion: The birch leafminer has been found for the first time in the Jilin area and has formed a regional infestation. In this study, the life history and soil ecological adaptations of the insect have been evaluated, and the spread of the insect is mainly restricted by environmental factors and soil water content, among which soil water content controls the amount and timing of adult eclosion, followed by soil pH and nitrogen content, while other physical and chemical properties basically presents little effect on adult eclosion after overwintering.

Key words: Profenusa thomsoni, soil water content, soil temperature, eclosion