Alfalfa leafcutting bee-Sapygid wasp

Sapyga pumila

Pest description and damage Sapygid wasps are tiny and black with yellow markings along the body. The first instar larvae of this wasp-like parasite is only about one tenth the size of the bee egg, but it is able to puncture the bee egg, either parasitizing the host or causing the host egg to collapse.

Management-emergence traps

Sapygid wasps will spend the night in bee holes but prefer to dwell in smaller holes. Night station traps target this behavior and are effective. They are made of hollow plastic pipes, containing insecticide inside, with small (2.5 mm diameter) holes. Sapygid wasps are attracted to the holes at night but once inside they are killed by the insecticide. White, light blue or green painted emergence traps placed in front of the bee nest are also effective at capturing sapygid wasps. Watch for these wasps in the spring and summer as that is when they are most active.

For more information:

Pitts-Singer T.L. and J.H. Cane. 2011. The alfalfa leafcutting bee, Megachile rotundata: the world's most intensively managed solitary bee. Annu. Rev. Entomol 56: 221-237.

R. R. James and T. L. Pitts-Singer. 2013. Health status of alfalfa leafcutting bee larvae (Hymenoptera: Megachilidae) in United States alfalfa seed fields. Environmental Entomology 42 (6): 1166-1173.

Pollen balls

Pollen ball is a common term used in the industry, which are basically failed (dead or no brood) provision filled cells in the nest. In United States losses vary from 4 to 42%. There can be many reasons for a specific pollen ball formation such as limited availability of nectar in foraging area and its relative concentration in the mass provision. Presence of weather conditions that are not suitable such as high temperature and humidity, problem gets aggravated in the presence of fungi. Position of the bee domiciles in the field, disorientation of the nesting bees, limited availability of the foraging resources in the fields which in turn can affect the relative concentration of nectar in the mass provision. overcrowding or high bee density of the bees in domiciles are some of the reasons for the formation of the pollen balls.

For more information:

M.S. Goettel, G.M. Duke, and G.C. Kozub. 2014. Characterization of "pollen balls" in commercial populations of the alfalfa leafcutting bee, Megachile rotundata in Canada, Journal of Apicultural Research 53:4, 496-499

T.L. Pitts-Singer. 2004. Examination of 'pollen balls' in nests of the alfalfa leafcutting bee, Megachile rotundata. Journal of Apicultural Research, 43:2, 40-46.

Pesticide poisoning

Pesticide poisoning is caused by the chemicals that are toxic or remain toxic in the environment for the longer periods. Leaf cutting bees are more sensitive to pesticide poisoning because they not only utilize nectar and pollen for feeding but also use leaf as building material for their nest. Due to which mother bee and brood remain in contact with the leaves for fairly long period of time. Neonicotinoids, fungicides, organophosphates, phenypyrazole (fipronil), growth regulator (Novaluron) have been reported to have negative impacts. Systemic insecticides like neonicotinoids are particularly have longer residual periods in the environment varying from few months to years.

Signs of pesticide poisoning:

Reduction in nesting by females

Presence of large mass of dead males near field domiciles


  1. Spray only when it is necessary and avoid spraying near and around flowers
  2. Follow the instructions on the label
  3. Spray, when bees are inactive (evening)
  4. Avoid spraying during windy, high dew point and low temperature days. Pesticides remain more persistent under such conditions
  5. Avoid buying chemically treated seeds especially neonicotinoid treated (being systemic they can express themselves in plant parts such as leaves, flowers and can be present in nectar and pollen)

For more information:

T.L. Pitts-Singer and J.H. Cane. 2011. The alfalfa leafcutting bee, Megachile rotundata: the world's most intensively managed solitary bee. Annu. Rev. Entomol 56: 221-237.

T. L. Pitts-Singer and J. H. Cane. 2011. Annual Review of Entomology 2011 56:1, 221-237

E. W. Hodgson, T. L. Pitts-Singer, J. D. Barbour. 2011. Effects of the insect growth regulator, novaluron on immature alfalfa leafcutting bees, Megachile rotundata, Journal of Insect Science, Volume 11, Issue 1, 1 January 2011, 43.