Cubital Index

Close-up of Apis mellifera forewing showing natural venation used in morphometric analysis.

Apis mellifera, F, wing, MD, Beltsville_2013-04-25, USGS Bee Lab

Introduction

In the world of biodynamic and sustainable beekeeping, preserving the genetic integrity of native honeybee breeds is of vital importance. One of the morphological markers used to assess breed purity is the cubital index (CI). This index, based on the geometry of wing veins, offers valuable insights into the ancestry and potential hybridization of honeybee colonies—without requiring advanced genetic testing.

The beauty of this method is that any beekeeper interested in the topic can learn how to determine the cubital index on their own bees, using simple and accessible tools (and plenty of patience).

Preliminary note

All the described methods are performed on dead bees, ethically sourced from within the hive or collected during hive work. The forewing can be removed immediately after finding a dead bee and stored in a labeled container until measurement.

The label should include hive ID, and if known, the genetic lineage (queen and drone origin), as well as the collection date.

Diagram of a honey bee wing showing labeled veins A and B for calculating the cubital index.

By Karl Udo Gerth - Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=8511129

What is the Cubital Index?

There’s already a wealth of information online about the cubital index, so we’ll keep it concise. The cubital index (CI) is a ratio derived from the lengths of two specific veins in the forewing of a honeybee. These veins form the cubital cell, a recognizable area near the wing’s leading edge.

Formula:

Cubital Index (CI) = Length of Vein A / Length of Vein B

Where:

• Vein A = the first cubital segment (longer segment)

• Vein B = the second cubital segment (shorter segment)

Cubital Index Labeling Confusion

Different sources use different labels for the two veins forming the third cubital cell in a bee’s wing.On this blog, the longer vein is labeled A, the shorter B (older convention), and the index is:

Cubital Index = A / B

Newer systems (like DAWINO) reverse this: A is the shorter, B the longer — same anatomy, different letters.

To avoid confusion, always check how A and B are defined before comparing values between studies.

Cubital index ranges and averages for four Apis mellifera subspecies used in wing morphometrics.

Microscope on wooden table in a beekeeping-themed lab with honeycomb decor and a bee at the window.

Microscope used for wing measurement and analysis.

Method 1: Measuring with a Microscope

The most accurate way to determine the cubital index is by removing a bee’s forewing and examining it under a stereomicroscope with at least 20x magnification.

The wing is mounted on a microscope slide using a drop of glycerin or a standard mounting medium and carefully positioned to expose the cubital cell. If a mounting medium is unavailable, clear adhesive tape (selotape) works as a temporary alternative.

Using a calibrated eyepiece or digital imaging software (affordable cameras that fit into the eyepiece slot are available), the beekeeper can measure the vein lengths and calculate the CI.

Pros:

✔ High precision

✔ Excellent for scientific documentation and breeding selection

Cons:

✘ Initial costs for microscope and measuring eyepiece (school-grade setups can suffice)

✘ Additional cost for camera

Note: If your apiary does not control drone lines and your queens are freely mated in nature, CI values may vary throughout the year depending on the mix of sperm in the queen’s spermatheca. In such cases, investing in expensive equipment might not be worthwhile.

Slide projector used to display enlarged bee wings for cubital index analysis on a white background.

Projector for displaying bee wings to measure cubital index.

Method 2: DIY Projection Technique

For those without lab access, here’s an effective, low-cost way to measure CI at home or in the field:

1. Wing Preparation:

Carefully detach the forewing from a dead bee. Mount it between two slide glasses, or tape it onto an empty slide glass (like a 35mm film slide) using clear adhesive tape.

2. Slide Projection:

Place the mounted slide into a slide holder and use a classic dia-projector to project the image onto a white screen or wall, just like projecting a photographic positive. The projector must be aligned precisely so that the light beam remains perpendicular to the wall in both horizontal and vertical planes. Any deviation in alignment may lead to distortion, compromising the accuracy of the results

3. Wall Projection:

The projected shadow reveals the cubital cell clearly enough to measure.

4. Manual Measurement:

Use a ruler to measure Vein A and Vein B directly on the projected image, and apply the same CI formula.

Pros:

✔ No need for lab-grade equipment

✔ Great for educational and personal use

Cons:

✘ Less accurate than microscopy

✘ Relies on older, often harder-to-find equipment

✘ Measurements may be affected by projection angle and focus

💾 Click the button below to download the Excel template for calculating the cubital index (CI) and analyzing wing vein data.