Effect of Trap-Nest Installation on Megachile Bee Abundance in Cowpea (Vigna unguiculata L.)

Abstract

Background: Megachile bees are important solitary pollinators of cowpea (Vigna unguiculata L. Walp.), however information on their species composition, abundance, effect of trap-nest installation, and impact of abiotic factors under subtropical environments remains limited. Aim: The present study was undertaken to assess the effect of trap-nest installation on above ground cavity-nesting Megachile bee abundance in flowering cowpea and to evaluate the impact of abiotic factors on their foraging activity. Methods: Observations on Megachile bees foraging on cowpea flowers were noted during two consecutive flowering seasons as pre- and post-trap-nest installation phases. The abundance was observed within a 1 m² area for 5 min at four-day interval, weekly abundance was calculated later. Analysis of variance, Pearson's correlation, and simple linear regression were employed to assess seasonal variation and the influence of weather parameters. Results: Four Megachile species (M. albifrons, M. bicolor, M. lanata and M. relata) were recorded foraging on cowpea flowers, with M. lanata being the dominant species during both seasons. The abundance of all species increased following trap-nest installation, with overall mean abundance increasing from 1.46±1.22 to 2.24±1.79 bees/m2/5 min. Bee foraging peaked in the 38th Standard Meteorological Week (SMW) during both phases before declining towards the end of flowering. The Megachile abundance exhibited a significant positive association with Minimum temperature (r = 0.931 and 0.936 during pre- and post-trap-nest installation phases, respectively) and explained the highest degree of variation in bee abundance. Conclusion: Trap-nest installation improved the abundance of Megachile bees in cowpea without altering species composition, while minimum temperature emerged as the key abiotic factor governing bee foraging. The outcomes highlight the potential of these trap nests as a tool for safeguarding above ground cavity-nesting pollinators and promoting sustainable pollinator management in cowpea agroecosystems.