3.5

HOW TO DETERMINE SIZE IN ALIVE STINGLESS BEES

By Márcia Ribeiro

Objective
In many situations is useful to determine the size of bees (see for example Ribeiro & Alves, 2001), but not always we can, or have the intention of sacrificing them in order to measure their size after they are dead. Therefore, this simple and quick method was developed to get the measurements from alive animals. Using a special apparatus (easy to build), it is possible to get some morphometric measurements without causing any harm to the bees, such as queens, workers or males. Manipulation causes no harm to the bees and they can be returned to their colonies soon after the measurements.

Fresh weight can also be obtained in order to determine the bees' size, because usually mass and morphometric measurements present a high Spearman's rank correlation coefficient (a non-parametric method is used because often these data are not normally distributed, for details on statistics see Zar, 1999).

Material
1. insect collector
2. plastic tubes with spongeous material at the extremities
3. analytical balance
4. stereomicroscope equipped with an ocular micrometer
5. apparatus for measurements (described bellow)
6. entomological tweezers
7. refrigerator

Fresh weight
Using a insect collector (fig. 1), the bee(s) to be measured can be easily collected at the nest, and placed into a plastic tube, previously weighed in the analytical balance (0.1mg) (fig. 2).

Morphometric measurements
Before the measurements each animal must be immobilized by low temperature (one minute at -8.0oC), at the freezer of the refrigerator. Then it must be put immediately into the apparatus and taken to the stereomicroscope equipped with an ocular micrometer. Usually, the bee will wake up quickly and therefore, the measurements must be done as soon as possible. Three measurements are normally easy and fast to do: maximum head width, medium interorbital distance (i.e., the distance between the eyes), and intertegular distance (i.e., the distance between the tegula, the insertion of the wings). When possible, a length measurement is also useful, but not always is easy to determine clearly where the thorax finishes and the abdomen starts (see Michener, 1965, for details on bee morphometry).

Description of the apparatus used to measure
This apparatus is made of a spongeous material, containing concavities of different sizes to accommodate the bee abdomen (obviously the larger cavities are adequate for queens, and the smaller ones for virgin queens, workers and males) (fig. 3). The spongeous material is supported by a metal structure, and when the bee is already placed in the cavity, a piece of glass must be put over it, in such a way to keep its head and thorax in a horizontal position for doing the measurements (fig. 4).


Fig.1. Bee collector with some bees already collected	Fig.2. Analytical balance

Fig. 3. Apparatus to measure the bees	Fig. 4. Queen in an adequate position, ready to be measured.

References

MICHENER, C.D. 1965. A classification of bees of the Australian and South Pacific regions. Bull. Amer. Mus. of Natural History, 130: 1-362.

RIBEIRO, M. DE F. & ALVES, D. DE A. 2001. Rev. Etologia, 3(1): 59-65.

ZAR, J.H. 1999. Biostatistical analysis. New Jersey. Prentice-Hall