Pests of Sugar Beet

Flea beetles

Species spectrum

Flea beetles (Coleoptera: Chrysomelidae) are tiny beetles, 1.5 – 4 mm long, they have enlarged thighs of the 3rd pair of legs and jump well (Šefrová, 2006). Larvae as well as adults are phytopagous, most of them oligophagous. Larvae tend to be more specialized. Adults can even be found on such plants where larvae do not develop. Usually, adults hibernate and form one generation (Čížek & Douget, 2008). More species of flea beetles from the genera Chaetocnema, Phyllotreta and Psylliodes can be found on beet (Novák, 1968). For flea beetles from the genus Chaetocnema is typical the following: oval body with noticeably bulging elytra, a tooth-shaped protuberance and distinctive ciliated incisures on the shins of the hind pair of legs used for jumping. The antennae are composed of eleven segments, the pronotum is without longitudinal grooves and the spots on elytra are arranged in longitudinal rows. Flea beetles in the genus Phyllotreta have oval-shaped body, eleven-segment antennae, pronotum with two longitudinal grooves and randomly arranged spots on the elytra. Hind shins are narrow, only at the end slightly concave. Flea beetles in the genus Psylliodes have an elongated arched body, antennae composed of ten segments, pronotum with two longitudinal grooves and spots on the elytra arranged in longitudinal grooves. The feet of hind legs are set in the shin. Distinctive features of the individual species are summarized in Tab. II. Only Chaetocnema concinna causes significant damage to beet. Very similar flea beetle Ch. picipes with the same bionomics differs, apart from the genitalia, also in the last spindle-shaped antennae segment. Ch. concinna has a flattened one. Ch. tibialis is found only infrequently in the warmest areas of our territory. Flea beetles of the genera Phyllotreta and Psylliodes are found on beet in dependence on weed infestation and the occurrence on neighbouring growths, but their damage to beet is insignificant (Fig. 3) (Novák, 1968; Šefrová, 2006; Čížek & Douget, 2008).

 

II: Main features of flea beetles occurring on beet (Novák, 1968; Čížek & Douget, 2008) 

Scientific name

English

name

Length of imago

Colour of imago

Preferred host plants

Chaetocnema concinna (Marsham, 1802)

brassy flea beetle, toothlegged flea beetle

1.82.5

bronze-coloured, less commonly greenish or copper-coloured

Polygonaceae

Chaetocnema picipes

Stephens, 1831

flea beetle

1.72.3

black bronze, rarely greenish or copper-coloured

Polygonaceae

Chaetocnema tibialis

(Illiger, 1807)

mangold flea beetle

1.62.2

black bronze, sometimes with copper or bluish shine

Amaranthaceae

Phyllotreta atra

(F., 1775)

turnip flea beetle

1.72.6

black

Brassicaceae, Resedaceae

Phyllotretanemorum

(L., 1758)

turnip flea beetle, large-striped flea beetle

2.43.1

black, yellow stripes on elytra, slightly inward curving at base, more prominently at apex

Brassicaceae

Phyllotreta nigripes

(F., 1775)

-

1.82.5

metallic blue, blue-green, rarely black

Brassicaceae, Resedaceae

Phyllotreta striolata

(F., 1803)

-

2.02.5

black, yellow stripes on elytra, narrowed in the middle from the outer side

Brassicaceae

Phyllotreta undulata Kutchera, 1860

small-striped flea beetle

1.82.5

black, longitudinal stripes on elytra, prominently curved towards the apex

Brassicaceae

Phyllotreta vittula (Redtenbacher, 1849)

-

1.52.0

black, pronotum with green or bronze shine, narrow stripes on the elytra

Brassicaceae, Poaceae, Asteraceae

Psylliodes chrysocephalus (L., 1758)

rape flea beetle, cabbage stem flea beetle

3.04.6

dark metallic blue, front part of the head reddish, forehead and vertex often dark

Brassicaceae

 

Fig 3: Damage caused by Flea beetles (photo by Šefrová)

 

 

Brassy flee beetle Chaetocnema concinna (Marsham, 1802)

 

Synonyms Chaetocnema dentipes (Koch, 1803), Chaetocnema laevicollis (C. G. Thomson, 1866), Tlanoma concinna Marsham, 1802. In German Rübenerdfloh, in Slovak skočka stavikrvová (Kůdela & Kocourek, 2002; Zicha, 2013).

 

Morphology

Imago is 1.8 – 2.5 mm long, shiny black-bronze, rarely metallic green or copper-coloured (Fig. 4) The ventral side is black. Dark filiform antennae are composed of eleven segments, the basal section is yellowish brown. The last segment of the antennae is flattened, especially in males. The pronotum is arched, narrowed in the front. The surface of the pronotum is matt and densely spotted. The elytra are widely oval and arched. On the elytra are longitudinal rows of spots, the gaps are shiny, very finely spotted. Thighs are black, shines brown, darker at the base, the feet are brown. The first segment of the feet of the first and second pair of legs is greatly enlarged in males (Čížek & Douget, 2008).The eggs are yellow, of elongated oval shape, 0.6 – 0.7 mm long and 0.2 – 0.3 mm wide. The surface of chorion is finely spotted and crinkled and composed of pentagon-shaped patches. Elongated white oligopod larvae (Fig. 23a) grow up to 4 – 5 mm long, the head, legs and sclerites on the prothorax and abdomen are black. The pupa is exarate (Fig. 23b), has three pairs of long setae on the head, and two pairs of setae on the mesothorax, metathorax and first six abdomen segments. The end of the body is protected by long urogomphi (Miller, 1956; Lasage & Majka, 2010).

 

Bionomics

Adults hibernate in different shelters, under leaves, moss, grass, under plant debris, in bushy areas and edges of forests. They leave their winter habitat in late March or early April, at temperatures above 8 – 9 °C. They start flying at the temperatures between 19 and 20 °C, at the height of 0.3 m. In sunny weather they fly, under worse weather conditions they hide at the base of plants, on the bottom side of leaves and in soil. After hibernation, they are not sexually mature, they copulate after maturation feeding. Soon after coupling, the females lay 1 – 6 eggs in the soil in the depth of 3 – 5 cm. From early June to July, each female lays 16 – 40 eggs. The eggs require high humidity, they perish quickly in dry conditions. Approximately after 2 – 3 weeks, larvae hatch, they develop on the roots and go through four instars. They pupate after 40 – 60 days in a fragile soil cocoon in the depth of 6 – 30 cm, deeper in drier soils. The pupa stage lasts 15 – 18 days. New adults hatch in late August, until September they feed on the leaves of plants from Polygonaceae and Amaranthaceae family, and then they seek winter shelters (Miller, 1956; Novák, 1968).

 

Distribution and Ecological Requirements

Chaetocnema concinna can be found in the whole of Europe with the exception of Iceland and Sardinia, in north Africa, in the Middle East, central Asia, in Kazakhstan, Mongolia, Russia and Siberia and Far East, in China, Korea and Japan. In 1980, it was introduced in North America. In the Czech Republic and Slovakia, it is one of the most abundant flea beetles in different biotops, in low-lands and uplands, preferring light sandy soils. Its development is favourably influenced by high temperatures in the summer and autumn. Chaetocnema concinna has, similarly to other flea beetles, a high number of antagonists attacking all developmental stages. As predators act the vertebrates (Grey Partdrige – Perdix perdix L., 1758) as well as invertebrates (Green LacewingChrysopa perla L., 1758); larvae of Entomognathus brevis (Van der Linden, 1829) develop on larvae of Chaetocnema concinna. Nematode Neoaplectana carpocapsae Weiser, 1955, infects larvae of Chaetocnema concinna with bacterium Achromobacter nematophilus Poinar & Thomas. Adults are infested by entomopathogenic fungi of the genera Laboulbenia and Dimeromyces (Čížek & Douget, 2008; Lasage & Majka, 2010).

 

Host Spectrum and Symptoms

Chaetocnema concinna was found on plants from different families (Amaranthaceae, Brassicaceae, Cannabaceae, Fabaceae, Poaceae, Polygonaceae, Rosaceae, Salicaceae), it prefers Polygonaceae plants and causes damage to beet. Females give preference to laying eggs to pale persicaria (Persicaria lapathifolia). Larvae develop on roots, adults gnaw out small pits in leaves, epidermis on the bottom side remains intact. Later, this epidermis dries out, so light green spots become apparent on the leaves. During growth, the epidermis cracks, and holes with browned edges 1 – 1.5 mm in diameter are formed . The feeding takes place mostly on leaves exposed to sun spread in horizontal or diagonal position. The least damaged leaves are those of the growing tip if obscured by larger leaves. In addition to gnawing out leaf tissue, they also suck its content. In more humid weather and light wind, adults usually damage the edges of leaf blades by gnawing out small pits. In warm and dry weather, when the soil is well heated up, adults settle on the bases of leaves and the feeding is also accompanied by sucking which causes dying of leaves and their parts. In good weather, one imago consumes on average 7 mm2 of leaf surface. The most significant damage occurs in young plants, later, from five-leaf stage onwards, the feeding of leaf beetles is less dangerous.

 

Importance

Chaetocnema concinna is a pest of germinating beet, the damage is caused by hibernating adults which gnaw out pits in the leaves in all areas of beet cultivation. Symptoms are more visible than damage caused by Atomaria linearis. The plants are weakened by the loss of leaf surface and delayed in their growth. In the case of outbreak, total defoliation may occur. Their harmfulness increases in dry periods. Larvae develop on roots, but are not harmful. In late summer, newly hatched adults consume different plants from the Amaranthaceae and Polygonaceae families, but have no significance in relation to beet (Novák, 1968). The first data on the harmfulness of flea beetles to beet in our territory comes from the year 1923 from Kolín (Fytopathologický ústav, 1924). Flea beetles as beet pests are also mentioned by Baudyš (1935) who assigned them a Czech name "brvorýžec", based on their characteristic ciliated incisures on middle and hind shins. Harmful occurrence of flea beetles on beet in the second half of the 20th century in our territory, according to the monitoring of ÚKZÚZ and SRS, is shown (Šefrová, 2004). In recent years, flea beetles have not been causing significant damage to beet. In 2008, low occurrence was detected in north Moravia and Silesia, moderate in south Moravia and high in Kutná Hora. In 2009, damage of germinating plants in the districts Brno – venkov and Blansko was observed. In 2010, Chaetocnema concinna was found on sugar beet in the districts of Karviná and Bruntál. In 2011 low occurrence was observed in early April in the districts of Pardubice, Česká Lípa, Liberec, Kladno and Kutná Hora and moderate in the districts of Olomouc and Opava in late April. In 2012 and 2013 isolated low occurrence was detected in several localities of our territory (Ministerstvo zemědělsvtí, 2013a).

 

Detection of Occurrence

 The occurrence of flea beetles on beet is detected from the beginning of growth germination until the formation of the first pair of leaves, i.e. until the beginning of the formation of the second pair of leaves in at least 50% of plants. The whole period lasts approximately 15 days. Adults can be observed in sunny weather by careful walking through the growth. In order to detect the occurrence of adults, sticky card traps can be used (in a vertical position or hanging transparent ones) or entomological nests spread 50 cm above the growth in sunny weather. In order to determine the number of adults on one plant based on feed marks, the following formula can be applied:

 

number of adults per plant = (the increase of feed marks on 1 plant / the number of days of adults' activity) x 1/7

 

Feed marks are counted during germination on plants in a bed 5x1m, the increase is usually determined 1 – 4 days after the first observation. Days of activity are sunny ones with temperatures above 7 °C. The increase of feed marks is divided by seven because one imago forms approximately seven feed marks per day (Novák, 1968; Kolektiv SRS, 1999).

 

Pest Control

Agrotechnical measures: Timely sowing in well-prepared soils speeds up the growth of young plants and decreases the danger of their damage because the plants can already be mature enough at the time of flea beetles invasion. Another principle is following crop rotation and deep ploughing. Sometimes the usage of weeds as so called distraction plants is recommended as well as the band application of herbicides, but only after germination.

Chemical protection: An effective protection against flea beetles is using treated seed material. As of 2013, the following substances are registered as effective against Atomaria linearis: tefluthrin (trade name Force 20 CS), thiamethoxam (Cruiser 70 WS), two-component instecticide of beta-cyfthurin and clothianidin (Poncho Beta FS 453.3). When the number of adults in the period from the start of germination until the start of the formation of the second pair of true leaves reaches critical levels, efficient two-component insecticide can be applied, with active substances chlorpyrifos and cypermethrin (Agrosales – Chlorpyrifos 550 EC, Nurelle D, Rapsody Duo, Runelle, Sniper – 550 EC, Spider – 550 EC). The critical number changes in dependence on the growth of beet, ranging between 0.08 on average per one plant with 3 mm long cotyledons and 18 with 45 mm long cotyledons (Ackermann et al., 2013; MINISTERSTVO ZEMĚDĚLSTVÍ, 2013b).

 

 

 

Fig.4: Imago of Chaetocnema concinna (Čížek and Douget, 2008)

 

 

 

 

 

 


 

 

The document was created: 28. 03. 2024 12:59:22
Source: http://web2.mendelu.cz/af_291_projekty2/vseo/