Colorado potato beetle
Beginner
Scientific Name
Leptinotarsa decemlineata
Identification
Adult beetles are somewhat rounded, about 10 mm long and 7 mm wide. Males are a few millimetres smaller than females. On the wing covers, 10 black stripes run lengthwise over a yellow-cream background.
Eggs are yellow, elongated and cylindrical. Egg masses have 25–40 eggs and are usually laid on the underside of the leaves. Recently laid eggs are bright yellow. Eggs turn dark orange close to hatching time.
Larvae are orange red and humpbacked, with two rows of black spots on each side of the body. There are four larval stages (instars).
First instar or newly hatched larvae are very tiny, about 1.5–2 mm long. First instar larvae feed first on the egg shells. After feeding on egg shells, first instars migrate to feed on the tender tissues of the growing point of the potato plant.
Second instar larvae are up to 5 mm long.
Third instar larvae are about 8 mm long.
Fourth instar larvae reach a maximum length of 12 mm. Fourth instar larvae are extremely voracious. Large larvae cause severe defoliation if left uncontrolled. Mature larvae drop to the ground to pupate.
Pupae, found only in the soil, are an inactive stage during which the mature fourth instar larva transforms into an adult.
Often Confused With
This is an insect that is never confused with any other pest.
Period of Activity
Beetles that overwinter and emerge in the spring are usually called “first generation beetles” and die 4–5 weeks after emergence. The beetles that emerge from pupae during the season—usually in July—are called “second generation beetles.” These second generation beetles feed continuously to accumulate enough energy to survive the winter buried in the soil. In southwestern Ontario, a partial third generation may develop if summer weather is unusually hot.
Scouting Notes
Begin checking for Colorado Potato beetles when the crop is emerging. Early in the season you probably will find adults and egg masses concentrated on border rows while the rest of the field is clean. If this is the case, record the number of rows where the beetles are concentrated and determine the average number of beetles per plant by examining 10 plants selected at random. This is important because it may be possible to treat only the border rows and not the entire field. Write this information on a data sheet, e.g. 8 rows in the west border of the field are heavily infested, with an average number of 5 beetles/ plant. Draw a map indicating the problem areas.
On sunny days, larvae and adults tend to feed on upper leaves. On cool days, they hide under the foliage.
Larvae and adults leave black droppings on the foliage
When no leaves are left, beetles eat pieces of stems. They also may feed on tubers left in the field after harvest.
Scout the field for CPBs even if a systemic insecticide was used as a seed treatment or in furrow. Collect any beetles found in the field before the expected loss of activity of the systemic insecticide.
Those beetles should be tested for resistance.
Thresholds
ECONOMIC THRESHOLDS FOR COLORADO POTATO BEETLE
| Number of CPB per 50 plant/stems | |||
|
Low |
Medium |
High |
Small Larvae |
- |
0-74 |
75 |
Large Larvae |
0-30 |
31-74 |
75 |
Adults |
0-15 |
16-24 |
25 |
Egg Masses |
4 egg masses in 50 plants is a potential problem |
||
Advanced
Scientific Name
Leptinotarsa decemlineata
Identification
Adult beetles are somewhat rounded, about 10 mm long and 7 mm wide. Males are a few millimetres smaller than females. On the wing covers, 10 black stripes run lengthwise over a yellow-cream background.
Eggs are yellow, elongated and cylindrical. Egg masses have 25–40 eggs and are usually laid on the underside of the leaves. Recently laid eggs are bright yellow. Eggs turn dark orange close to hatching time.
Larvae are orange red and humpbacked, with two rows of black spots on each side of the body. There are four larval stages (instars).
First instar or newly hatched larvae are very tiny, about 1.5–2 mm long. First instar larvae feed first on the egg shells. After feeding on egg shells, first instars migrate to feed on the tender tissues of the growing point of the potato plant.
Second instar larvae are up to 5 mm long.
Third instar larvae are about 8 mm long.
Fourth instar larvae reach a maximum length of 12 mm. Fourth instar larvae are extremely voracious. Large larvae cause severe defoliation if left uncontrolled. Mature larvae drop to the ground to pupate.
Pupae, found only in the soil, are an inactive stage during which the mature fourth instar larva transforms into an adult.
Often Confused With
This is an insect that is never confused with any other pest.
Biology
Life stages: eggs, larvae, pupae, adult.
The Colorado potato beetle (CPB) is one of the most serious insect pests of potatoes. The feeding damage caused by CPB will drastically reduce yield if no effective control is applied.
Weather conditions determine the number of CPB generations per season. If cool temperatures prevail (15–16°C), CPB completes its life cycle in about 8 weeks. By contrast, at high temperatures (30–33°C), CPB populations increase rapidly because the incubation period of the eggs and the time for development of larvae and pupae is shortened. In Ontario, CPB generally completes two generations during the growing season. In warm summers, a third generation may develop.
In the fall, adult beetles burrow into the soil either in potato fields or in protected places surrounding the fields to overwinter at depths of 25–35 cm. When beetles emerge in the spring, most walk to the crop. If the weather is warm, a few beetles will fly directly to the fields.
The infestation and feeding damage of CPB is first noticed along the edges of potato fields close to overwintering sites. If spring weather is warm, beetle emergence may be very rapid; during cool springs, beetle emergence may be quite slow.
On warm, sunny days, beetles are easily observed feeding on top of the plants, but on cool days they hide under soil clods or foliage.
Mating and egg laying occur shortly after emergence. Females may lay as many as 400 eggs during their life span of 4–5 weeks. The yellow eggs are laid in clusters, usually on the underside of leaves. Frost will kill the eggs, as will sandy soil splashed by heavy rain onto the egg masses.
Eggs hatch into larvae within 4–9 days, depending on temperature. Larvae are reddish with a distinct black head, humped back and double row of black dots on each side of their bodies. The larvae pass through 4 stages (instars), reaching maturity in 7–20 days, depending on temperature. Once the fourth-instar larvae have matured, they crawl down to the ground and bury themselves in the soil to a depth of 5–10 cm to pupate. The pupal stage lasts 5–9 days. The next generation of adults then emerges.
Period of Activity
Beetles that overwinter and emerge in the spring are usually called “first generation beetles” and die 4–5 weeks after emergence. The beetles that emerge from pupae during the season—usually in July—are called “second generation beetles.” These second generation beetles feed continuously to accumulate enough energy to survive the winter buried in the soil. In southwestern Ontario, a partial third generation may develop if summer weather is unusually hot.
Scouting Notes
Begin checking for Colorado Potato beetles when the crop is emerging. Early in the season you probably will find adults and egg masses concentrated on border rows while the rest of the field is clean. If this is the case, record the number of rows where the beetles are concentrated and determine the average number of beetles per plant by examining 10 plants selected at random. This is important because it may be possible to treat only the border rows and not the entire field. Write this information on a data sheet, e.g. 8 rows in the west border of the field are heavily infested, with an average number of 5 beetles/ plant. Draw a map indicating the problem areas.
On sunny days, larvae and adults tend to feed on upper leaves. On cool days, they hide under the foliage.
Larvae and adults leave black droppings on the foliage.
When no leaves are left, beetles eat pieces of stems. They also may feed on tubers left in the field after harvest.
Scout the field for CPBs even if a systemic insecticide was used as a seed treatment or in furrow. Collect any beetles found in the field before the expected loss of activity of the systemic insecticide.
Those beetles should be tested for resistance.
Thresholds
ECONOMIC THRESHOLDS FOR COLORADO POTATO BEETLE
| Number of CPB per 50 plant/stems | |||
|
Low |
Medium |
High |
Small Larvae |
- |
0-74 |
75 |
Large Larvae |
0-30 |
31-74 |
75 |
Adults |
0-15 |
16-24 |
25 |
Egg Masses |
4 egg masses in 50 plants is a potential problem |
||
Management Notes
Rotate crops and avoid planting potatoes adjacent to beetle overwintering sites (previous year’s potato or tomato field).
Conduct tests for resistance (dip tests, spraying tests) before applying insecticides. CPB has a tremendous ability to develop resistance to crop protection materials.
Effective insecticides applied at planting either as seed treatment or in-furrow are recommended when first generation CPB are expected to be high.
A number of cultural control practices such as trenches lined with plastic or trap cropping can help to reduce pesticide use.
