Through our feedback mechanism on the BioProtection Portal, CABI has recently discovered that growers in Kenya are experiencing problems with bean fly (Ophiomyia spp.). We have put together this information article about the fly to help you recognize it, prevent it from becoming a pest, and manage it effectively once it has become a pest.
How can you identify bean fly?
Known commonly as bean fly or bean stem maggot, this insect’s scientific name is Ophiomyia spp. including O. phaseoli, O. spencerella and O. centrosematis.
Bean fly is a small shiny, metallic bluish-black fly, about 2mm in length with clear wings. The larvae are yellow-white in colour and 3mm in length. Pupae are barrel shaped and 2-3mm long. They are initially yellow with dark ends but become dark brown (O. phaseoli) or shiny black (O. spencerella) or red-orange (O. centrosematis).
Which plants does bean fly attack?
The larvae of this small, bluish-black fly attack the stems and leaves of leguminous plants, including Common bean (Phaseolus vulgaris).
What damage does bean fly do?
Initial damage shows on the leaf surface with small pale yellow areas due to adult feeding and ovipositioning (egg-laying). Heavy infestation may lead to leaf drop.
Emergence of the larvae leads to the development of mines (lined marks) on the leaf, as the larvae feed. The main damage is caused by the larvae feeding in the stem as the larvae move down to the lower stem. This may cause swelling and splitting of the stem. In severe attacks the plant can lodge (collapse), wilt and die. If the plant survives, it will have reduced growth and yield. It may produce adventitious roots (roots that form from non-root tissue) to compensate for the damage. Yield loss can be up to 100%.
What is the bean fly’s life-cycle?
The bean fly life-cycle consists of egg, larva, pupal and adult stages.
Larvae create feeding tunnels and just beneath the epidermis of the leaf and/or stem. The larval stage (three instars) can last from 8-10 days depending on the temperature (up to 11 days for O. centrosematis).
Pupae are formed in the stem feeding tunnels and the period of pupation can vary depending on conditions from 7-20 days. Adults emerge and mating begins within 2-3 days.
How do you manage bean fly?
You can manage bean fly through prevention and direct control. Non-chemical methods include:
Direct biological control options are also available. For more information, see: www.bioprotectionportal.com
Direct control may also include conventional chemicals (systemic). Check local pesticide lists for availability.
More information on the bean fly, its distribution, life-cycle and management can be found on the Plantwise Knowledge Bank, Infonet biovision, Plantix, Business Queensland and in a recent review by Nkhata et al. (2018)