Brevicoryne brassicae Family: Aphididae
Common name: cabbage aphid
Life cycle: Generations per year: up to 15 during growing season
Description: A minute, soft-bodied, sap-sucking insect; elliptical in shape, becoming more round as it matures through the nymph stages. Has six, long, thin legs; two long, six-segmented antennae which are carried over the body; sucking mouthparts called stylets which are enclosed in a sheath called a rostrum; a pair of very short, upright, backward-pointing tubes called cornicles (or siphunculi) located on the 5th or 6th segment of the abdomen; a shorter projection called cauda located above the anal plate. The cabbage aphid is greyish-green in colour.
Aphids have a complicated life cycle. In temperate climates, overwintering eggs hatch in spring. The first generation of wingless females (called stem mothers) are already pregnant…reproducing by parthenogenesis (without fertilization). The offspring are born live, called viviparity…a unique phenomenon in this insect. Stem mothers continue to reproduce throughout the summer, typically giving birth to 5 or 6 nymphs per day.
When the host plant becomes overcrowded, or its resources reduced, some of the offspring will develop into adults and grow two pairs of large, clear, membranous wings. Once able to fly, these winged adults, called alates, leave the host plant in search of another, fresh plant.
In northern climates, towards the end of the season, the stem mothers produce both male and female offspring. This is timed to dropping temperatures and lowering light levels as the season winds down. After mating, the females lay their eggs in the plant debris of the host plants at soil level, where the eggs will overwinter. (In warmer climates, there is no egg stage in the aphid life cycle. The stem females reproduce continuously throughout the year.) Cabbage aphid eggs are black in colour.
Special Notes: Originally native to Europe, the cabbage aphid is now found worldwide.
It is generally thought aphids have been on the planet for roughly 280 million years, placing them in the early Permian period. The oldest aphid fossil was found several years ago in China…an almost complete insect, minus part of the antennae and part of its legs. It has been determined to be a completely new species of aphid and named Dracaphis angustata. The aphid fossil was dated and found to have actually lived during the Middle Triassic Age…after the Permian period.
To explain some of the body parts on the aphid…the cornicles, or siphunculi, those slightly elevated, slender protrusions on the back of an aphid, are defensive apparatuses which will exude a fluid that hardens when it comes in contact with air as a deterrent to predators. The substance is also thought to contain alarm pheromones.
The shorter cauda tube, located above the anal opening, serves to collect the honeydew excreted from the anus and hold it raised so it does not foul the body.
Host plant list: Cabbage aphids are a particular pest to cabbage, cauliflower, broccoli, Brussels sprouts, rape, radishes, numerous mustards, and kale.
Remedial Actions: There are several predator insects which hunt aphids…lady beetles, ant-lions (green lacewing larvae), yellow jackets, European paper wasps, and others.
Organically…usually a strong jet of water from the hose, repeated every few days, will dislodge these pests. If possible, and if there are no beneficial insects feasting on the aphids, grasping the affected area of branch between two fingers and sliding them up the branch will squish many of the offenders. Same goes for rubbing fingers over infested leaves.
Another plan of attack is to hit the aphids with a soapy water solution…2 teaspoons (10 ml) of dish soap into 4 cups (1 L) of water, but first check to see if there are any beneficial insects present before you start spraying.
Concentrated, repeat forays against this pest are required in order to eradicate them. With the fast turnaround in their reproduction cycle, their numbers can get out of hand very quickly.
Posted on November 8, 2018