FLEA BEETLES
(Coleoptera: Chrysomelidae)
Flea beetles are common posts of cruciferous crops on the prairies. Flea beetles are characterized by enlarged hind femora and their jumping behaviour (Burgess, 1977).
A field key for separating the 5 flea beetle species commonly attacking canola in the prairies is given in Burgess (1977).
Flea beetle eggs are small (0.4 mm), elongate, and yellow. Larvae are a dirty-white color with brown heads and end plates. Mature larvae are slender, up to 6 mm long, with three pairs of short legs on the thorax. The pupae are white and about 2.4 mm in length.
The adult beetles of the 3 most common species are described below: i.e.,
Cabbage Flea Beetle
The cabbage flea beetle, Phyllotreta albionica, is a small, shining, metallic-green or bronze beetle, measuring slightly over 2.5 mm in length (Dustan, 1932). There are 11 antennae segments. The 5th antennae segment is longer than the 4th or 6th in the female beetle and longer and broader than the 4th or 6th in the male beetle Burgess, 1977). There are no stripes on the elytra.
Crucifer Flea Beetle
The crucifer flea beetle, Phyllotreta cruciferae, is a small, blakish beetle with a bright blue lustre, measuring about 2-3 mm in length. There are 11 antennal segments. The 5th antennal segment is not longer or broader than the 6th in either sex of this flea beetle (Burgess, 1977). There are no stripes on the elytra.
Striped Flea Beetle
The striped flea beetle, Phyllotreta striolata, is a small, blackish beetle with a distinct yellowish stripe on the elytra, measuring about 2-3 mm in length. The elytral stripe is narrow, incurved at the base, and does not extend to the posterior edge of the elytron. There are 11 antennal segments. The 5th antennal segment is not longer or broader than the 6th in either sex of this flea beetle (Burgess, 1977).
Cabbage Flea Beetle
The cabbage flea beetle is distributed across southern Canada (Chittenden, 1927; Beirne, 1971).
Crucifer Flea Beetle
Introduced into North America from Eurasia in the 1920's, the crucifer flea beetle is now distributed across the grasslands of southern Canada and the northern U.S.A. (Chittenden, 1927; Brown, 1967;Beirne, 1971, Burgess, 1981).
Striped Flea Beetle
Introduced into North America from Eurasia before 1801, this species is now distributed across southern Canada and the northern U.S.A., southward into California (Chittenden, 1927; Brown, 1967, Beirne, 1971;Burgess, 1931). It is most common in the parkland areas across the northern edge of the prairies.
Adult beetles overwinter under dead leaves and crop remnants, often in hedges and woodlots near their host plants (Burgess, 1977, Turnock et al., 1987).
Cabbage Flea Beetle
The cabbage flea beetle's hosts include cabbage, turnip, cauliflower, kale, Brussels sprouts, canola, and related vegetables (e.g., sugar beets; tomatoes; radish-, potatoes) and weeds (e.g., flixweed, wild mustard) in the cruciferid group (Dustan, 1932; Burgess, 1977,1982).
Crucifer Flea Beetle
The crucifer flea beetle's hosts include cabbage, turnip, cauliflower, kale, Brussels sprouts, canola, and
related vegetables (e.g., sugar beets; tomatoes; horseradish radish, potatoes) and weeds (e.g., fixweed; peppergrass; wild mustard; stinkweed; lamb's quarters) in the cruciferid group (Dustan, 1932; Burgess,1977, 1982). It has often been reported as the most abundant flea beetle on canola in the prairies (Burgess, 1977).
Striped Flea Beetle
Host plants include cabbage, turnip, cauliflower, kale, Brussels sprouts, canola, and related vegetables (e.g., sugar beets; tomatoes; horseradish; radish; potatoes), weeds (e.g., fixweed; peppergrass; wildmustard; stinkweed, lamb's quarters), and even mosses (Dustan, 1932; Burgess, 1977, 1982).
It has often been reported as the second most abundant flea beetle on canola in the prairies (Burgess, 1977, 1982).
Burgess and Wiens (1976) describe their method of rearing the striped flea beetle on horseradish in the greenhouse.
Generally, flea beetles overwinter as adults under leaf litter, along fence rows, and in shelterbelts and woodlots. They become active again in April and early May. Initially, they may feed on volunteer canola and mustard or on weeds (e.g., wild mustard, fixweed or peppergrass). Later, the flea beetles move to seedling canola or other cruciferous crops.
Mating occurs in May. Egg-laying follows in late May and early June. Their eggs are laid in batches of up to 25, on or in the soil. Subsequently, the overwintered adults begin to die off. The young larvae feed on the roots of the developing canola for 3 or 4 weeks. They are present from about mid-June to late-July.
After feeding, the larvae form earthen cells in which they pupate. The new adult flea beetles begin emerging in late-July and early-August. These adults feed on the green tissue of suitable host plants that are still present. The feeding activity of these adults can continue into mid-October. However, by mid-September, most adults have usually entered a dormant, overwintering stage. Only one generation of flea beetles is produced each year.
Cabbage Flea Beetle
Adult cabbage flea beetles overwinter in the soil in fields, fence-rows and woodlots. Mating and egg-laying occur in the early spring. The eggs are laid in the ground at the bases of host plants. The overwintered adults die in late June or early July.
The newly-hatched larvae live in the soil, feeding on the roots of host plants. Root feeding does not usually cause much commercial damage. Mature larvae pupae in the soil. The now adults emerge in late July or early August. These adults may damage late-maturing crops. There is only one generation per year.
Crucifer Flea Beetle
Adult crucifer flea beetles overwinter in the soil in fields, fence-rows, hedges, shelterbelts, and woodlots (Westdal and Romanow, 1972; Burgess, 1977, 1981; Surge: and Spurr, 1984). Turnock et al. (1987) examined winter survival of flea beetle adults.
Mating and egg-laying occur in the early spring, adults first appearing in early April (Burgess, 1977). The eggs are laid in batches of about 25 eggs in moist soil at the bases of host plants (Westdal and Romanow, 1972). The overwintered adults die in late June or early July.
The newly-hatched larvae live in the soil between early June and early August, feeding on the roots of host plants. Root feeding does not usually cause much commercial damage.
Mature larvae pupae in the soil in mid-July. The new adult emerge in late July or early August. These adults may damage late-maturing crops. Burgess (1977) reported that they will attack any green host plants that exist. On canola, they may riddle the leaves with holes and chew the epidermis from stems and pods. There is only one generation per year.
Striped Flea Beetle
Adult striped flea beetles overwinter in grass and leaf litter in fence-rows, hedges, shelterbelts, and woodlots (Westdal and Romanow, 1972; Burgess, 1977, 1981; Burgess and Spurr, 1984). Turnock et al. (1987) examined the winter survival of striped flea beetle adults.
Mating and egg-laying occur in the early springs adults first appearing in mid- to late-April (Burgess, 1977). The eggs are laid in moist soil or on the roots of host plants (Westdal and Romanow, 1972;Burgess, 1977). The overwintered adults die by late June (Burgess, 1977).
The newly-hatched larvae live in the soil between early June and late July, feeding on the roots of host plants. Root feeding can cause serious damage (Burgess, 1977).
Mature larvae begin to pupate in the soil in mid-July. The new adults emerge in late July or early August. These adults may damage late-maturing crops. Burgess (1977) reported that, on canola, they may riddle the leaves with holes and chew the epidermis from stems and pods.
Development from egg to adult may take 26-28 days (Burgess, 1977). There appears to be only one generation per year (Burgess and Wiens, 1975).
6. Seasonal Abundance:
Flea beetles are most noticeable in the early spring, when the leave overwintering sites to feed on seedlings, and in mid-August, when the new generation of adults emerge. Lamb (1983), using suction traps, found that the highest catch of crucifer flea beetles occurred in late August and early September. In home gardens, they are most noticeable when they invade gardens as they are forced off nearby swathed fields.
7. Responses to Environmental Factors:
Flea beetles feed most actively when the weather is sunny, warm and dry. Cool, damp weather reduces the intensity of attack and favours plant growth.
Shade, as found in a dense crop stand, discourages feeding (Burgess, 1977). In such situations, feeding is usually limited to the tops of plants that are exposed to direct sunshine.
Burgess (1 977) noted that adults of the crucifer flea beetle were netted on the wing from early May until early October in Saskatoon; 14C was the lowest temperature at which flight was observed.
Similar findings were reported by Lamb (1983) for overwintered adults but not for newly-emerged adults. He found these adults flying at temperatures as low as 4.7C. He also observed a negative correlation with, windspeed and flight.
Turnock et al. (1987) found that temperature has an effect oil fall emergence and survival but not on the overwintering survival of crucifer flea beetles.
However, shade, as found in a dense crop stand, does not seem to discourage feeding by the striped flea beetle, as reflected in its presence in parkland and boreal forest habitats (Burgess, 1982).
Burgess (1 977) noted 15C was the lowest temperature at which flight of the striped flea beetle was observed. Most flight activity occurs below 6.5 m above ground (Burgess, 1982).
Most damage to canola is done by the overwintered adult beetles just before or soon after the seedlings have emerged from the soil. Flea beetles move into newly emerging canola crops from the borders by hopping when the temperature is below about 18C and flying when the temperature is higher. Other species attack potatoes, peppers, tomatoes and sugarbeets but the life cycles and damage are similar.
They feed by chewing small holes in the cotyledons or leaves. Damaged plants typically have a "shot-hole' appearance when the tissues around the feeding sites in the cotyledons and leaves die.
Losses, from flea beetle feeding on young seedlings, include reduced number of plants surviving, smaller and weaker plants, and delayed plant development. All of these losses contribute to reduced yield, especially if the weather is hot and dry.
Canola seedlings can withstand significant leaf area remove in the cotyledon stage under good plant growing conditions without significant reduction in yield. With heavy and continuous attacks, seedlings may wilt and die. This is especially true when feeding is combined with poor plant growth during hot, dry weather. Heavy infestations may destroy the entire crop and reseeding may be necessary. Once the crop reaches the 3- or 4-leaf stage, the plants are generally established and can outgrow the feeding damage. Also the number of adult flea beetles often begin to decline at that time.
Flea beetle damage to garden crops is similar in the spring but may be more serious in the fall because the leaves remain greener longer. Much damage can occur when field crops are harvested and horded of hungry flea beetles move in to home gardens to feed.
Cabbage Flea Beetle
Cabbage flea beetles attack the roots and leaves of crucifers. The larval stage lives in the ground and feeds on the roots; the adults feed on the leaves, producing ‘shot holes’. The most serious damage is caused by the overwintered adults that attack seedlings in he spring. Movement of these beetles into crops often takes the form of a creeping invasion moving from plant to plant into the field or of a mass invasion flight into the field (Burgess, 1977). Serious feeding damage results in wilting and death of the affected seedlings. Partial or complete crop failures can occur.
In western Canada, this species occasionally attacks canola but is not as important as Phyllotreta cruciferae, the most abundant and serious pest. Flea beetles will cause damage to canola pods and stems in mid-August.
Crucifer Flea Beetle
Crucifer flea beetles attack the roots and leaves of crucifers. The larval stage lives in the ground and feeds on the roots; the adults feed on the leaves, producing ‘shot holes’.
The most serious damage is caused by the overwintered adults that attack seedlings in the spring. They can reduce plant stands, reduce plant vigour, delay maturity and reduce the quality and quantity of crop yield.
Movement into canola crops often takes the form of a creeping invasion moving from plant to plant into the field or of a mass invasion flight into the field (Burgess, 977). Serious feeding damage results in wilting and death of the affected seedlings. Partial or complete crop failures can occur.
In western Canada, Phyllotreta cruciferae is the most abundant and serious flea beetle post attacking canola. Flea beetles will cause damage to canola pods and stems in mid-August. Damaged pods may ripen and shatter earlier than undamaged pods.
Striped Flea Beetle
Striped flea beetles attack the roots and leaves of crucifers. The larval stage lives in the ground and feeds on the roots; the adults feed on the leaves, producing ‘shot holes’.
The most serious damage is caused by the overwintered adults that attack seedlings in the spring. They can reduce plant stands, reduce plant vigour, delay maturity and reduce the quality and quantity of crop yield.
Movement of flea beetles into canola crops often takes the form of a creeping invasion moving from
plant to plant into the field or of a mass invasion flight into the field (Burgess, 1977). Serious feeding damage results in wilting and death of the affected seedlings. Partial or complete crop failures can occur.
In western Canada, Phyllotreta striolata is the second most abundant and serious flea beetle pest attacking canola. Flea beetles will cause damage to canola pods and stems in mid-August. Damaged pods may ripen and shatter earlier than undamaged pods.
Cabbage Flea Beetle
Cabbage flea beetles are likely preyed on by big-eyed bugs, larvae of the green lacewing, melyrid beetles, field crickets, and damsel bugs, based on various studies of the crucifer flea beetle (Gerber and Osgood, 1975; Burgess, 1977, 1980, 1982; Burgess and Hinks, 1987).
Crucifer Flea Beetle
Crucifer flea beetles are likely preyed on by big-eyed bugs (Geocoris bullatus), larvae of the green lacewing (Chrysopa carnea), melyrid beetles (Collops vittatus), field crickets (Gryllus pennsylvanicus), and damsel bugs (Nabis alternatus), based on various studies of flea beetle predation (Gerber and Osgood, 1975; Burgess, 1977, 1980, 1982; Burgess and Hinks, 1987). However, it is unlikely that these predators have much impact on flea beetle infestations.
Striped Flea Beetle
Striped flea beetles are likely preyed on by big-eyed bugs (Geocoris bullatus), larvae of the green lacewing (Chrysopa carnea), melyrid beetles (Collops vittatus, field crickets (Gryllus pennsylvanicus), and damsel bugs (Nabis alternatus), based on various studies of flea beetle predation (Garber and Osgood, 1975, Burgess, 1977, 1980, 1982; Burgess and Hink, 1987). However, it is unlikely that these predators have much impact on flea beetle infestations.
II. MANAGEMENT
1. Population Monitoring Techniques:
A variety of techniques have been used for estimating populations and studying behaviour in the field (Burgess, 1977). Adult flea beetles can be collected with a sweep net, suction traps and sticky traps (Lamb, 1983). Larvae and pupae can be recovered from soil by water flotation. Emergence cages can be placed over the soil in overwintering sites or field crops to capture adults. Saucer traps, containing water and some detergent, can be placed in fields to follow flea beetle movements.
Burgess (1981) and Burgess and Spurr (1984) describe their methods for collecting flea beetles from the soil-trash of overwintering sites. They collected as many as 2 million overwintering beetles per hectare.
Allyl isothyocyanate, a mustard oil, has been used as an attractant for trapping crucifer-feeding flea beetles (Burgess, 1980, 1981).
Flea beetle abundance and related damage can be assessed in a variety of ways also. One can count the number of plants per meter of crop row, collect all beetles down the center row of a test plot, count the number of feeding holes on collected leaves, etc.
Although the different sampling methods and materials used help to understand the behaviour and ecology of crucifer flea beetles, none of them seem to provide reliable estimates of population density. Most methods yield highly variable results.
2. Threshold/Action Population Level:
No economic thresholds guidelines are available for most crops attacked by flea beetles.
Daily inspection of newly-emerged crops is necessary to identify flea beetle damage as it develops. Generally, if flea beetles are numerous on the plants or on the soil, if beetle feeding damage is over 50%of the cotyledon or leaf area, and if the weather is warm and dry, a foliar-applied insecticide may be necessary. If damage is only along the field margins, then controls may be restricted to damaged areas only.
Foliar-applied chemicals may be required to protect susceptible vegetable seedlings in the spring. In canola, control is usually warranted when typical damage is seen on 15-20% of the pods.
3. Management Alternatives - Non-Chemical:
Cultural controls have little effect on flea beetle populations. Clearing cruciferous weeds from fence-rows and headlands may help by removing alternative sources of food. Removing vegetative trash from fields may reduce overwintering sites.
Increasing seeding rates and allowing cruciferous weeds to grow in summerfallow fields may help in reducing damage if flea beetle populations are high.
Attempts to develop flea beetle resistant crops are being made by Agriculture Canada (e.g., scientists are trying to produce a canola that is resistant, because of a repellent or anti-feedant, to the crucifer flea beetle in Manitoba).
4. Management Alternatives -Chemical:
Flea beetles can be controlled by using in-furrow granular treatments, seed treatments, residual foliar insecticides, or combinations of these treatments, being sure to observe any pro-harvest intervals.
The use of recommended seed treatments will provide some control and protection to the emerging canola seedlings.
Foliar-applied chemicals may be required to protect susceptible vegetable seedlings in the spring.
Agricultural insecticides registered for flea beetle control include the following active ingredients: i.e.,
Note that some of the above insecticides are restricted to use against certain flea beetles and specific crops. Always check the container label to be sure the right material is being used.
Flea beetles invading home gardens in late August, moving from swathed canola fields, can be controlled using rotenone dusts. Rotenone has a 1-day wait period on garden produce.
In-Furrow and Seed-Coating Treatments
The following recommendations are for seed-drill application and are not valid for application with discer seeders. The lindane treatment may have to be followed by a post-emergence foliage spray about 7 days after seedling emergence).
Rate Preharvest
(g Al/ha) Interval
Carbofuran
(Granular)..... 225-280 -
Lindane (seed
dressing)...... 16 g/kg -
Terbufos (granular)
(granules mixed with seed).. 280-560 -
The granular formulations of Furadan include Furadan 5G and Furadan CR-10.
Foliar Sprays for Canola
Yellow mustard seedlings are fairly resistant to flea beetle attack and should not require treatments with insecticides at seeding. The foliar insecticides usually recommended for flea beetles on canola are given below: i.e.,
Rate Preharvest
(g @NI/ha) Interval
BEFORE POD FORMATION:
Azinphos-methyl
Canola........... 70 30
Carbaryl
Canola........... 540 -
Carbofuran
Canola........... 70-140 60
Mustard.......... 70-140 21
Cypermethrin......... 35 30
Deltamethrin......... 5-7.5 14
Malathion
Canola and
Mustard.......... 560 7
Methidathion
Canola and
Mustard.......... 175 30
Malathion............ 560 7
Restrictions and Precautions -
Azinphos-methyl: Do not apply when bees are foraging. Do not re-enter treated fields without protective equipment within 2 days of application.
Carbaryl: Seedling application only. Do not apply tank-mix combinations unless your previous experience indicates the mixture is effective and will not result in application problems, excessive residues, or plant injury.
Carbofuran: Do not apply at 70 g/ha more than twice to the same crop, nor at the 140 g/ha rate more than once. May be applied by air or ground equipment. Has both systemic and contact action usually with quick results. Furadan 48OF is compatible with fungicides commonly used on the same crops. May be tank mixed with phenoxy ester or amine herbicides and used only on crops listed on both labels. Highly toxic to bees, waterfowl, birds, fish and other wildlife. Do not apply Furadan to areas where bees are actively foraging or near apiaries. The use of Furadan 48OF may be hazardous to burrowing owls. Do not apply within 250 m of known burrowing owl nests.
Cypermethrin: Avoid application at temperatures above 25c. Only one application per year by air. Very toxic to bees, fish, and aquatic organisms.
Deltamethrin: Do not feed treated crop to livestock. Do not apply at temperatures above 25c. Do not make more than 3 applications per year (Only one application per year by air). Both Decis 5ECand Decis 5F are registered for the control of flea beetles in canola. Note that only the Decis 5EC formulation is registered for flea beetles in mustard.
Malathion: Do not apply at air temperatures below 20c. Do not apply when bees are foraging.
Methidathion: Observe a 100 m setback from any body of water or environmentally sensitive area when applying by air. Toxic to birds, bees, fish and other wildlife. Do not apply to crops in bloom. Do not enter treated fields on the same day of application. Do not f led or allow animals to graze on treated crops. Apply in minimum of 110 L water/ha by ground, or 22 L water/ha by air.
Terbufos granules (Counter [2.2-4 kg/acre]) are also register for flea beetle control in canola and mustard. Apply by blending the seed and granules in a mechanical mixer or stirring with a stick in the drill box. Use higher rates for flea beetle control if extreme infestations are anticipated or if using a discer or air seeder. Counter 5G may be mixed with fungicide treated seed. Treated seed must not be used for feed or oil processing. Excess treated seed should be used up by double planting.
Flea Beetles in Potatoes
Carbaryl (e.g., Sevin XLR Plus [0.5 1/acre]) is registered for the control of flea beetles in potato. There is a 7-day waiting period before harvest. Sevin is of moderate acute mammalian toxicity and is highly toxic to bees. Avoid contamination of food, food, water supplies, streams and ponds.
Cypermathrin (e.g., Cymbush [0.055 1/acre]) is also registered for flea beetles in this crop. There is a 7-day waiting period before harvest.
Deltamethrin (e.g., Decis 5EC [0.04-0.06 1/acrai) is registered for the control of the potato flea beetle in potatoes. There is a 23-day waiting period before harvest.
Disulfoton (e.g., Di-Syston [6-9 kg/acre with granules or 1.1-1.9 1/acre with the liquid concentrate]) is also registered for the control of the potato flea beetle in potatoes. There is a 90-day waiting period before harvest. For granular applications, place granules in the seed furrow or in a band on each side of the seed furrow at planting. Application may also be me de as a side dressing either above or with fertilizer after plants become established. Use higher rates in organic soils. For liquid applications, apply as a water emulsion or with liquid fertilizer as an in-furrow spray or injection on each side of the seed furrow at planting, or inject as a side-dressing after plants become established. Use higher rates inorganic soils.
Carbofuran (e.g., Furadan 48OF [0.445 1/acre]) is also registered for the control of potato flea beetle in potatoes. There is a 7-day waiting period before harvest.
Chlorpyrifos (Lorsban 4E [0.405 1/acre]) is also registered for the control of potato flea beetle in potatoes. There is a 7-day wafting period before harvest. It may be applied by air or ground equipment. Lorsban 4E has a high acute mammalian toxicity. It is very toxic to bees, fish, birds, aquatic organisms and other wildlife. Do not apply or drift on to workers or other persons. Do not apply directly to water or where runoff could occur to adjacent aquatic sites. Avoid use when bees are actively foraging.
Methidathion (Supracide 10.5 1/acre]) is also registered for the control of potato flea beetle in potatoes. There is a 14-day wafting period before harvest. It may be applied by air or ground equipment. It works as a contact and stomach poison. Observe a l00 m setback from any body of water or environmentally sensitive area when applying by air. Do not apply to crops in bloom. Do not enter treated fields on the same day of application. Do not feed or allow livestock to raze on treated canola or sunflower crops.
Phorate (Thimet) is registered for the control of potato flea beetle in potatoes. Distribute granules evenly in furrow or granules may be banded on each side of the row at planting time. Use the low rate for sandy or light soils and the high rate for silt or heavy soils. Phorate works as a systemic poison with effective initial residual activity on soil and foliar insects.
Endosulfan (Thiodan) is registered for the control of flea beetles on potatoes. There is no pre-harvest interval. It may be applied by air or ground equipment. Thiodan has a high acute mammalian toxicity, is toxic to bees and is highly toxic to fish.