Factors influencing flea beetle damage
Flea beetle feeding damage was similar for striped and crucifer species. Carabid and spider predators helped to reduce feeding damage, especially at low plant populations. Feeding damage increased as temperatures increased, while less damage was observed at higher plant populations.
Striped and crucifer flea beetles are chronic pests of seedling canola that cause millions of dollars feeding damage, in addition to the millions of dollars spent on seed and foliar insecticides. However, predatory feeding might help to control or slow flea beetle feeding. Research was conducted at the University of Manitoba, Department of Entomology, to fill knowledge gaps in how generalist predators and ambient temperatures affect flea beetle feeding on canola.
Striped and crucifer flea beetles were collected with sweep nets one to two weeks before each trial, and striped flea beetles were also collected from colony-reared cages. Colony-reared striped flea beetles used in the research were four to nine days of age. Predators were collected using live pitfall traps set in canola fields. All flea beetles and predators were not fed for 24 hours before the trials.
Canola seeds were planted into plastic trays and grown until they reached the cotyledon growth stage. Two seedlings were then grown in a covered microcosm pots for experiments 1, 2 and 4.
Temperature and flea beetle species effects
Experiment 1 looked at the effect of temperature and flea beetle species on canola damage. Four constant temperatures of 13C, 18C, 23C, and 28C were compared at 70 ± 5 per cent relative humidity, and a 16:8 light:dark rotation. Damage from five introduced striped or crucifer were assessed and compared to a control with no flea beetles.
As temperature increased so did the amount of flea beetle damage with by far the most damage occurring at 28C. The least damage occurred at 13C and damage at 18C and 23C were intermediate and similar. Damage from both species increased similarly as temperatures increased. Feeding damage on the upper and lower cotyledon surfaces were similar at all temperatures.
Temperature and plant density effects
Experiment 2 looked at the effect of temperature and plant density on canola damage. Two temperatures of 18C and 28C were compared at the same relative humidity and light:dark rotation as Experiment 1. Two plant densities of five or 10 canola plants were compared. Five colony-reared striped flea beetles were introduced to the microcosm, and compared to a no-flea beetle control. Flea beetles were removed after 24 hours.
Defoliation damage was greater at the low plant density and a temperature of 28C. At 18C, cotyledon damage was similar at both low and high plant densities. There was also more stem damage at 28C with a low plant density, but damage was similar at low and high plant densities at 18C. Cotyledon defoliation significantly predicted stem damage.
Flea beetle predation
Experiment 3 looked at the effect of predation on flea beetle survival. Generalist predators included carabids and spiders. One predator and three striped plus three crucifer flea beetles were placed in plastic petri dishes with two canola cotyledon plant materials. Flea beetle survival was counted after 24 and 48 hours.
Two carabid species, Harpalus amputatus, Pterostichus melanarius, and two spider species, Pardosa spp. and Pirata spp., significantly reduced the number of flea beetles in the petri dish trials.
Mean number of flea beetles alive after 48 hours with a variety of predator genera from the families Carabidae and Lycosidae
Source: Woodland et al. 2025.
Predation and plant density effects
Experiment 4 looked at the effect of predation and plant density on canola damage. Twelve rounds of microcosm experiments were conducted, with the first seven rounds having three plants per pot, while the last five rounds also included six plants per plot. One predator and six flea beetles were added to each pot, and compared to a predator-free control after 48 hours.
In the first seven rounds with low canola plant density, P. melanarius and Pardosa spp. reduced flea beetle abundances. P. melanarius also reduced the mean number of flea beetles at high plant densities.
The presence of predators Pardosa spp. and P. melanarius resulted in less overall cotyledon defoliation and damage intensity (percent defoliation when only considering damaged plants) from flea beetles compared to the predator-free control group. Flea beetles also caused less overall stem damage and stem damage intensity with P. melanarius than in the controls.
Overall, the four experiments showed the value predators in helping to control flea beetle populations and in reducing their feeding damage, especially at low plant populations. Feeding damage for both crucifer and striped species increased with higher temperatures. Both flea beetle species preferred feeding on the undersides of cotyledons; however, the difference in percent damage was less than 1%, suggesting that current scouting techniques that assess surface damage is adequate.
The researchers concluded by recommending that “field studies are needed to determine the potential of increasing generalist predator field populations through conservation biological control approaches, in combination with increasing seeding rates and other agronomic techniques, to reduce flea beetle damage to canola crops.”
This work was supported by the Canola AgriScience Cluster Program. Shayla Woodland received research funding from the University of Manitoba Undergraduate Research Award, the James Gordon Fletcher Graduate Fellowship, and the University of Manitoba Graduate Completion Award. Denice Geverink received funding from the Dr. J.A Garland Summer Research Award in Agricultural and Food Sciences.
Woodland S, Geverink D, Costamagna AC. Generalist predators, increased plant density, and lower temperature reduce flea beetle (Coleoptera: Chrysomelidae) damage to canola (Brassicaceae) stems and cotyledons. The Canadian Entomologist. 2025;157:e41. OPEN ACCESS: https://doi.org/10.4039/tce.2025.10023
Photo courtesy Canola Council of Canada
