Wild bees of Brunei Darussalam

Abstract

The wild bee fauna of Borneo and Brunei is singularly depauperate compared with other tropical areas but very rich in the two bee groups at the zenith of social insects. In the forests of Belalong I found 4 Apis and 22 stingless bee species; the latter, mostly Trigona, included 76% of all stingless bee species known from Borneo, and all three endemics. Other bee species probably number about 80 if the proportions of the highly social bees found in Indonesia apply to Belalong. A ‘rapid assessment’ of the highly social bee fauna was possible in Brunei, even during rainy weather in November, by spraying sugar and salt baits on vegetation. Virtually every species of Trigona, Apis and Pariotrigona came to these baits during a few days. Assays of various salt solutions revealed the following preferences by the stingless bees (predominantly Trigona melina) and honey bees (predominantly Apis koschevnikovi and A. dorsata): Na > Mg > K > NH₄ > PO₄. Preference for sodium, magnesium, and potassium is possibly linked to neural transmission requirements, osmotic water balance and low levels of these elements in soil, expressed directly in the nectar and pollen that bees consume. Apis koschevnikovi was found to be similar to African and other tropical cavity-nesting Apis in showing the highest profitability (measured as energy harvest rate of sucrose solutions) at 45% sugar solutions, compared with solutions as low as 15% and as high as 65% sugar. Ground-level surveys of bee nests located 33 colonies of stingless bees along 12 km of trails. I calculate the density of stingless bee colonies to be approximately 3 per hectare - lower than the 4 to 6 colonies in each hectare found in some Neotropical forests. The sugar-salt baiting technique also revealed the first known association between an orchid and the genus Apis. Apis koschevnikovi was found with a small orchid pollinarium attached to its scutellum, thus it may have a pollinator role often played by Trigona in the neotropics for a few orchid genera. Other noteworthly bees were the large, nocturnal Xylocopa myops, megachilids and long-tongued Amegilla, all likely principal pollinators of obligately outcrossing tree species.