Diversity, Development and Management of Insect Galls: Insights into Gall Infestation on Silkworm Food Plants

Abstract

Galls are unusual swellings or outgrowths of plant tissues that result from the activity of various organisms such as insects, mites, fungi, and bacteria. These structures arise due to chemical and mechanical stimuli that disrupt the plant’s hormonal balance, particularly involving growth regulators such as auxins and cytokinins. Among all causative agents, insects are the predominant gall inducers, manipulating plant tissues to form nutritive and protective habitats for their immature stages. The North Eastern Region of India, being rich in sericultural biodiversity, supports the rearing of all four commercially important silks—Mulberry, Eri, Muga, and Tsar—where host plant health plays a critical role in silk yield and quality.Gall-inducing insects, such as midges and psyllids, attack economically important silkworm host plants like Persea bombycina (Som), Litsea polyantha (Soalu), and Litsea salicifolia (Digloti), leading to gall formation that adversely affects the nutritional value of leaves and thereby impacts silkworm development. Notably, Asphondylia spp. and Pauropsylla beesoni are identified as key pests forming galls on Som and Soalu, respectively. The "Nutrition Hypothesis" suggests that gall tissues offer enhanced nutritional value over regular plant tissues, supporting insect growth and reproduction. While galls are generally host- and organ-specific, their formation results in physiological stress and damage to the host plants, including reduced photosynthesis and structural deformities. Understanding gall formation, insect-plant specificity, and effective management strategies is crucial for maintaining the health of silkworm host plants, especially in sericulture-dependent regions. Sustainable control methods and continued research into resistant plant varieties are key to mitigating the impact of gall-inducing insects on silk productivity.