Biston, Leach, 1815

Assessment of Biston View in CoL and Clanis damage in Erythrophleum fordii trees

Field observations were carried out on Biston and Clanis during 2024 in 2 to 16-year-old E. fordii plantations in Hanoi, Hoa Binh and Bac Giang provinces, Vietnam. Life-cycle laboratory studies were used to compliment the field studies, and this was undertaken in the SPFH, Hanoi, Vietnam. The E. fordii plantations examined being damaged by Biston and Clanis were 10 – 20 hectares in size, typically with 1,660 trees per hectare. In each province, 10 plots/age (each 500 m 2) were randomly selected and leaf damage from Biston and Clanis larvae was recorded on 60 trees in each plot. The damage was classified at five levels as follows: 0 = no leaf damage; 1 = leaf area loss <25%; 2 = leaf area loss 25 to <50%; 3 = leaf area loss 50 to <75%; and 4 = leaf area loss ≥ 75%.

Data analysis

Following the results of damage classification, the damage incidence (P%) was calculated using Equation 1 ( Chi et al. 2021):

P% = (n/N) × 100 (1) where: n is the number of trees attacked by leaf-feeders; N is total number of trees assessed.

The damage severity (R%) in each plot was calculated using Equation 2 (VAFS 2023):

R% = (( Ʃni × vi)/(N × V)) × 100 (2) where ni is the number of infected trees at damage index i, vi is the damage index at level i, N is total number of trees assessed, and V is the maximum damage index used for classification.

The damage severity level was ranked based on the average damage index as follows: very severe damage (R%> 75%); severe damage (75% ≥ R%> 50%); medium damage (50% ≥ R%> 25%); slight damage (25% ≥ R%> 0%) and no damage (R% = 0%).

Results