Distribution of threshold values of harmfulness of larvae of lamellar phytophages in time

Goal. Clarification of the threshold of harmful larvae for 2-year-old pine seedlings at different stages of the growing season. Methods. Phenological observation of the complex of plates of the phylogenetic phytophages: eastern and western, marble, red and shaggy worms. Methods of compilation of phenological maps and graphic modeling of harmfulness thresholds of phytophages. Results It has been established that the period of harmfulness for larvae of the plates of the breeding phytophages, depending on their phenology, during the vegetation is expediently divided into three stages: A (spring), B (mostly summer), C (autumn), which correspond to different models of thresholds of harmfulness. In particular, the model for the autumn period takes into account the increased likelihood of plant death due to the suppression of larvae of the crust in the spring and summer period and the effectiveness of the measures implemented to regulate their numbers. The system for regulating the number of phytophages should be aimed at maximal protection of the pine culture in period A — prevention of damaging the root system of larvae (chemical insecticide) and preventive saturation of the ecosystem with biological agents in such a way that their maximum efficiency is at period B. Conclusions. For the spring, mainly summer and autumn periods, it is expedient to use different models of hazard thresholds: for the spring and summer x = (0.96y + 0.63) / 3, and for the autumn x = ((0.96y + 0.63) / 3) × 0.577, where — x — ratio of the biomass of the root system to the biomass of the larvae; y — biomass of the root system. The hazard threshold model for the autumn period takes into account the increase in the likelihood of plant death due to the weakening of the crustal larvae in previous periods (spring, summer) and the effectiveness of the measures taken to regulate the number of these phytophages.