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Bug of the Month – Potato Psyllids


By: Dan Johnson

Insect pest monitoring offers some interesting lessons in how we might benefit from keeping close tabs on the crop environment. This year was a good example. Surveyors continued sampling potato fields for an invasive combination, the potato psyllid (Bactericera cockerelli) and the bacteria this small bug can transmit, Candidatus Liberibacter solanacearum (Lso). The pathogen can cause zebra chip of potato, a recent problem in the USA, and it is also considered a high priority pest of potatoes and tomatoes in New Zealand and Australia.

Sampling in Canada began in 2013 with sticky cards at locations across southern Alberta, by a network of University of Lethbridge staff, Scott Meers and staff at Alberta Agriculture and Forestry, agronomists, sampling services, and growers. No potato psyllids were found. The survey was expanded to more potato fields in 2014, and still no potato psyllids were found. In 2015, small numbers of the potato psyllids (but free from the Lso bacterium) turned up in late summer in Alberta, and the following year we also found potato psyllids on sticky cards sent by network participants in Manitoba (Vikram Bisht and staff) and Saskatchewan (Jazeem Wahab and Greg Larson). 

In 2017, potato psyllid numbers greatly increased, and appeared in 70% of 45 sites that we regularly sampled in southern Alberta. Unfortunately, potato psyllids at several locations were found to contain the Lso bacterium, detected by analysis of DNA in Larry Kawchuk’s lab, at the Lethbridge Research and Development Centre.

The good news is that the community of natural enemies that kill aphids, leafhoppers, thrips, and psyllids was healthy and active, offering some crop protection. These natural enemies, mainly predaceous bugs, beetles, spiders, and parasitoids (mainly small wasps), thrive where insecticide spraying is kept to a minimum.

We assembled basic methods for forecasting development and activity of potato psyllids and their enemies, using weather data, but the results of 2018 still came as a surprise. The cool weather in April and May set back development of plants and insects more than in any year in the past decade. Temperature swings from warm conditions in early April, to the deep freeze of -14 C in mid-April, followed by 15-20 C, probably caused disruption and mortality for many insect pests that were waking up from winter hibernation (diapause). Very few potato psyllids survived, and the offspring of the survivors were well behind schedule. We found other species that could carry the pathogen, but also in very low numbers. Natural enemies of pests, such as ladybird beetles and predaceous bugs, were also reduced in numbers, but seemed to recover. I checked with Hugh MacLean, weather research technician at the Lethbridge Research and Development Centre, and he noted that the cold spring also hit a lot of trees and crops hard this spring. If I am right that we owe this break in the potato insect problem to a combination of weather and natural enemies, it would make sense that we continue to monitor these conditions with valid scientific approaches, to help predict future challenges, and find sustainable solutions.