Challenges from the European Wireworm

By Joanna MacKenzie, M.Sc.

Walking through a recently planted grain field, your eyes fall upon a stretch of yellowed seedlings. Bending over to look more closely, you tug at a plant only to pull it out of the ground, its roots severed. Looking closer still, you see it: It lurks just beneath the surface of the soil, a seemingly innocent although ubiquitous, worm-like creature with a hardened yellow surface. Plucking it out of the soil, the creature lays quietly in your hand, seeming to pose no threat. Yet, in your hand you now hold the insect responsible for countless crop losses across Canada: the wireworm. The two eyespots on its hind end betray its true identity…it is a European wireworm, the most ravenous of the species. They were introduced to Canada in the soil ballast once used to steady empty ships as they returned from the Old to the New World to load up on lumber. Unfortunately, these small creatures have had a profound effect on agricultural systems.

After many destructive years in the soil, the wireworm pupates, emerging the following spring as a click beetle. In contrast to the larval stage, the adult click beetle is short-lived, inconspicuous and docile. Named for their ability to right themselves by flipping into the air with an audible snap, click beetles survive only long enough to mate and lay their eggs that hatch to release wireworms.

Wireworms are notoriously indiscriminate in their food choices, being attracted to the carbon dioxide emitted by any growing vegetation in the soil. Combine this voracious appetite with a lengthy lifecycle, up to five years, spent dwelling in the soil and you have a very destructive creature. Countless crops are vulnerable to attack. Preferring the warm, damp soil conditions that prevail in the spring and autumn the wireworm migrates to the soil surface, only to retreat to the depths when the soil becomes too dry or cold. This movement renders crops such as grains susceptible to wireworm attack in the early stages of growth, and also puts late harvested root crops at risk in the fall feeding period. It has been suggested that up to a quarter of potato crop losses in North America can be attributed to wireworm feeding, riddling the surface and flesh of the tuber with holes and rendering the crop unmarketable.

Potent and environmentally persistent insecticides were once used to silence the wireworm, but the removal of many organophosphate-based pesticides from the Canadian market has left crops vulnerable to wireworm attack. Alternative strategies have been attempted with varying levels of success, such as altering the timing of planting or harvest in an attempt to avoid peak feeding periods, timing tillage operations to target the eggs and newly hatched larvae that constitute the most susceptible periods in the wireworm life history, instituting biological control measures, and the employment of trap crops.

Many farmers’ crops, as well as the Organic Agriculture Centre of Canada (OACC) research plots, have been seriously challenged by wireworm feeding. Therefore, staff rallied to develop alternative cultural management strategies to tame the wireworm and mitigate damage, strategies that can be employed by organic and conventional producers alike.

OACC, in conjunction with Agriculture and Agri-Food Canada, is examining the potential for the incorporation of unattractive or damaging crops in a cash crop rotation to reduce wireworm levels in infested fields. Crops under evaluation include brown mustard that contains compounds harmful to the wireworm, flax that may be nutritionally inadequate to support larvae, alfalfa that may create an inhospitable soil environment with its water wicking root system, and buckwheat with a rapid growth rate that may be amenable to tillage at those times at which wireworms are most susceptible. Research is also targeted at the development of a strategy in which wireworms can be pulled away from a root cash crop through the use of an attractive bait crop, pushed away through the use of compounds that may invoke plant defenses against herbivory or otherwise limit wireworm feeding, or immobilize through the disruption of the wireworm lifecycle.

Contemplating the history and significance of the creature that you still hold in your hand, you decide to take action. With a satisfying squish, one less wireworm will damage your crop. Now to tackle the rest!

 

Joanna MacKenzie, M.Sc., is a Research Associate at the Organic Agriculture Centre of Canada. Please send comments or questions by phone to 902-893-7256 or by email to oacc@nsac.ca.

Posted September 2008

 

“We gratefully acknowledge funding support from Agriculture and Agri-Food Canada for for production of this publication. Agriculture and Agri-Food Canada (AAFC) is pleased to participate in this project. AAFC is committed to working with industry partners to increase public awareness of the importance of the agriculture and agri-food industry to Canada. Opinions expressed in this document not necessarily those of the OACC or AAFC.”