Influence of cropping cycles and plant strata of French bean, Phaseolus vulgaris (Fabaceae) on oviposition behaviour of legume pod borer, Maruca vitrata (Fabricius) (Lepidoptera: Pyralidae) and its parasitoid association from highland ecosystem

Abstract: The legume pod borer, Maruca vitrata (Fabricius), is a major pest of legume vegetables including French bean (Phaseolus vulgaris) and can cause significant yield losses if left unmanaged. However, there is limited data on its oviposition behaviour across different cropping cycles and plant strata as are influenced by weather conditions and plant strata by food availability. This study investigated the oviposition patterns of M. vitrata in five cropping cycles (C1–C5) and three vertical plant strata (60, 90, and 120 cm) of P. vulgaris by egg abundance in the Cameron Highlands, Malaysia and examined their relationships with recorded rainfall data. Larval abundance was also monitored to complement the oviposition data. Weekly rainfall and humidity data were also recorded for each cycle. French bean flowers were collected from nine planting beds (22 planting points per bed), dissected under a stereomicroscope, and the number of M. vitrata eggs was counted. Data were analysed using two-way ANOVA and Tukey’s test (p < 0.05). Results showed no significant difference in the number of eggs oviposited between cropping cycles (p = 0.853), although the highest egg count (235.7 ± 44.6) occurred during the cycle with the lowest rainfall (94.4 mm), and the lowest egg count (185.1 ± 90.5) during the cycle with the highest rainfall (307.4 mm). In contrast, egg numbers differed significantly between plant strata. The number of larvae also varied significantly between cycles (p = 0.01). Additionally, the parasitoids Triclistus aitikini and Therophilus javanus were recorded in the three crop cycles, with no significant difference in their occurrence across cycles (p = 0.56), but a significant difference between strata (p = 0.01). These findings highlight the importance of managing plant height or supporting structures to reduce M. vitrata infestation effectively.

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