Biology, ecology and dynamics of Deborrea malgassa (Heylarts 1884) (Lepidoptera: Psychidae), the main threat to apple Malus domestica Borkh growing in Madagascar

Abstract The biology, ecology and population dynamics of Deborrea malgassa (Heylarts 1884) (Lepidoptera: Psychidae), a bagworm moth increasingly impacting apple orchards in the Highlands of Madagascar, were studied with a view to seeking control strategies. A combination of larval rearing under semi‐controlled glasshouse conditions and systematic field surveys over several regions of the Highlands of Madagascar, including monthly monitoring of infestation across three apple‐growing sites in Antsirabe II district over 2 years, was implemented. The results showed that the distribution of D. malgassa is mainly found in the Vakinankaratra region as polyphagous. The lifecycle was 177 to 233 days, development for the species, marked by a long larval stage with a low survival rate compared with the other stages. The wingless female can lay an average of 796.07 ± 28.96 larvae. The sex ratio is skewed in favour of the males, with 2.39:1. Population dynamics showed marked seasonal fluctuations, with infestation peaks in May to August corresponding to the cold dry season and apple tree phenological stages of leaf fall and dormancy. These findings provide insights into the bioecology of D. malgassa and support the design of environmentally friendly pest management strategies adapted to highland orchard systems.