Influência de visitantes florais de Bertholletia excelsa Humb. & Bonpl. (Lecythidaceae), castanheira-do-Brasil, sobre o comportamento de forrageio de Xylocopa frontalis e Eulaema rnocsaryi (Hymenoptera: Apidae)

Abstract

Bertholletia excelsa Humb. & Bonpl. (Lecythidaceae), has self-incompatible flowers, and therefore needs the efficiency of its pollinators to successfully implement its pollination. This study was conducted at the farrn Aruanã (3 O S 58 O 45 "W), in the municipality of Itacoatiara, Amazonas, and aimed to investigate the influence of flower visitors on visits and stays of Xylocopa frontalis (Xylocopini) and Eulaema mocsaryi (Euglossina) to flowers of B. excelsa. The observations and collections of data were made on three different trees during a period of three months fiom November 2006 to January 2007. Voucher collections of flower visitors and behavioral observations of visits X fiontalis and El. mocsaryi were made on three consecutive days in each of the three individuals during the period from 05:OO a.m. to 11 :O0 a.m.. Seven behaviors were selected for each of the bees, X frontalis and El. mocsaryi, which were: a) hovering in front of the flower in the presence of stingless bees; b) opening (or not) the flower; c) abandoning (or not) the flower; d) running off stingless bees from inflorescences; e) withdrawing from flowers occupied by beetles and trips; f ) evaluating the frequency of consecutive visits to flowers where the two individuals alternate between X frontalis and El. Mocsaryi; g) antagonism between X frontalis and El. mocsaryi. Each of the seven behaviors studied (a, b, c, d, e, f, g) was recorded 60 times in each period of observation from November 2006 to January 2007 totaling to 1260 records of activities for each of the focal bee species. Individuals of X frontalis (n = 1 8) and El. mocsaryi (n = 18) had their palynological loads acetolyzed. After this, the pollen loads were mounted on glass slides with glycerinade gelatin and then fixed the slides with paraffin. Palynologial samples were identified by comparison with reference material fiom the Pollen Library at INPA. The results show that: a) 37% of X frontalis and 20% of El. mocsaryi display hovering behavior in fiont of the flowers in the presence of stingless bees (x2 = 37.09, p <0.01); b) 15% of X frontalis and 2% of El. mocsaryi opened the flowers in the presence of stingless bees (x2 = 18.67, p <0.01); c) 85.5% of X frontalis and 94% of El. mocsaryi left the flowers when they noticed the presence of stingless bees (x2 = 224.45, p <0.01); d) 3% of X frontalis and 0% of El. mocsaryi ran off the stingless bees from inflorescences (x2 = 6.10, p <0.05); e) 3% of X frontalis and 2% El. mocsaryi not left the flowers with beetles and trips housed (x2 = 1.02, p> 0.05); f ) 97% of X j?ontalis and 99% El. mocsaryi not visited flowers where both visited (x2 = 1.3 1, p> 0.05); g) 1% of X fiontalis and 4% of El. mocsaryi tried to move away fiom each other (X2 = 4.60, p <0.05). The palynological analysis indicated that X frontalis transported large quantities of grains of B. excelsa (> 79%) in the crop, while El. mocsaryi transported less than 7.5% of the pollen loads of B. excelsa. However, the plants of secondary vegetation belonging to the family Solanaceae and Melastomataceae have been widely exploited by El. mocsaryi. It follows that the X pontalis and El. mocsaryi are significantly influenced in their visiting behaviors to the flowers of B. excelsa when in the presence of other insect visitors-primarily stingless bees. In the presence of stingless bees, X frontalis and El. mocsaryi avoid visiting many flowers of a single individual and therefore are "forced" to visit other plants within the crop, including other Brazil nuts (B. excelsa). Thus, the influence exerted by stingless bees can contribute, eventually, to cross-pollination of B. excelsa. The secondary vegetation has been important in keeping the pollinators in the area of cultivation and possible raising of X JTontalis in the town can be promoted.