Snake gourd (Trichosanthes anguina L.) is an important cucurbitaceous vegetable valued for its nutritional, medicinal and functional properties; however, its productivity is constrained by limited availability of superior planting materials and infestation by diverse insect pests. The present investigation was undertaken to evaluate yield and yield-attributing traits, determine the seasonal incidence and infestation pattern of major insect pests, and identify promising putative mutant lines of snake gourd with superior agronomic performance. The experiment was conducted at the Horticultural Research Station, Mondouri, Nadia, West Bengal, during January–May 2020–2021. Fifteen genotypes comprising 14 putative mutant lines and the Nilgunj local control were evaluated in a randomized block design with three replications. Observations were recorded on vine length, internodal length, days to first male and female flowering, days to first fruit harvest, sex ratio, fruit length, fruit girth, number of fruits per plant, average fruit weight and fruit yield per plant. The incidence of major insect pests was monitored at five-day intervals throughout the crop period. Substantial variability was observed among the mutant lines for growth, flowering, fruit and yield attributes. Vine length at 90 days after sowing ranged from 265.0 to 427.7 cm, with ML6 recording the maximum value. ML13 exhibited the shortest internodal length (11.11 cm), whereas ML7 showed the longest (16.04 cm). ML11 and ML5 were the earliest lines for first fruit harvest, requiring 88.34 and 89.32 days, respectively. ML3, ML11 and ML13 recorded comparatively lower male: female sex ratios than the control. Fruit length ranged from 38.32 to 56.00 cm, while fruit girth varied from 9.47 to 12.64 cm. ML13 produced the maximum number of fruits per plant (11.50), whereas ML7 recorded the highest average fruit weight (503.34 g) and fruit yield (2.87 kg plant⁻¹), followed by ML13 (2.59 kg plant⁻¹) and ML12 (2.54 kg plant⁻¹). A diverse insect-pest complex comprising red pumpkin beetle, fruit fly, Epilachna beetle, aphids, whitefly, caterpillar, thrips, mirid bug, snake gourd semilooper and leaf miner was recorded. Red pumpkin beetle was most abundant during early February, whereas fruit fly incidence increased markedly after fruit formation and reached a peak during late April (11.11 flies plant⁻¹). Epilachna beetle population increased during April, while whitefly, thrips and semilooper populations were comparatively higher towards May. Pest incidence showed varying relationships with temperature, relative humidity and rainfall. Overall, the study demonstrated considerable genetic variability among the putative mutant lines and identified ML7, ML13 and ML12 as promising genotypes for further evaluation and utilization in snake gourd breeding programmes, particularly for improving yield under insect-pest-prone conditions.