Dynamics of pest populations in winter rapeseed crops in Belarus

Winter turnip rape (Brassica campestris var. oleifera) is becoming an increasingly sought-after oil crop in the Republic of Belarus. Its seed is used for the production of vegetable oil, which is used for food purposes, the manufacture of margarine, canned goods, confectionery and bakery products, as well as for technical needs and the production of biofuel. Oilcake and meal are processed into valuable protein concentrates for feed production.

Why winter turnip rape needs protection from pests

The soil and climatic conditions of the republic are very favorable for the cultivation of this crop. However, the expansion of sown areas and the achievement of stable yields are hindered by the lack of phytosanitary data. Until recently, there was no detailed information in Belarusian farms on the species composition and the number of pests specifically on turnip rape crops.

For timely crop protection, it is necessary to constantly monitor the phytosanitary situation. Monitoring of the entomological situation was carried out in 2022–2023 in various agro-climatic zones on winter turnip rape crops of the Veronika cultivar. Specialists recorded the population density of dominant pests during the autumn and spring growing seasons, noting phenological growth stages according to the BBCH scale.

Weather dynamics and species composition of phytophages in crops

Weather directly affects insect activity. For example, the warm autumn of 2022, with air temperatures 5.2–6.6 °C above the long-term average and precipitation within 103–115%, created optimal conditions for the spread of pests. In contrast, the spring of 2022, with cold weather in April and May, slowed down vegetative processes.

In the spring of 2022, the transition of the average daily temperature through +10 °C was delayed. It occurred only in the third ten-day period of April to the first ten-day period of May, which is one to two weeks later than usual. The hydrothermal conditions of the 2023 spring period were also heterogeneous: while the first ten-day period of May turned out to be cold, the subsequent ten-day periods passed with a precipitation deficit.

• Flea beetle activity period — germination – emergence
• Appearance of turnip sawfly — 3–4 leaf phase
• Average temperature of winter 2022/2023 — -1.6 °C
• Precipitation for winter 2022/2023 — 187 mm
• Temperature of May 2023 — +13.3 °C

During the autumn growing season, flea beetles are among the first to appear in the crops. During seed germination and seedling emergence, the crop is attacked by the cabbage stem flea beetle (Psylliodes chrysocephalus L.), as well as cruciferous flea beetles — the wavy flea beetle (Phyllotreta undulata Kutsch.), the blue flea beetle (Ph. nigripes F.), and the black flea beetle (Ph. atra F.). Later, starting from the 3–4 true leaf phase of the winter turnip rape, the false caterpillars of the turnip sawfly (Athalia rosae L.) begin to cause damage to the plants.

Our studies established that in the autumn period of 2022–2023, an increase in the population of the cabbage stem flea beetle was observed in winter turnip rape crops. The cabbage stem flea beetle belongs to the Coleoptera order. The beetle is bluish-black in color and 3–4 mm long. The larva has a brown-black head, three pairs of legs, and two terminal projections at the rear of the abdomen. The host plant for the phytophage is many overwintering cruciferous weeds, such as wild mustard, shepherd's purse, etc. Feeding, oviposition, and larval development can occur at both high and low temperatures. The imago gnaws circular holes in the cotyledons and the first pair of true leaves, leaving the epidermis intact. But the main damage is caused by larvae, which damage the growing point by mining it from the inside, which in turn becomes a site for the penetration of various fungal diseases, subsequently leading to significant winterkilling of plants. In August–September, the cabbage stem flea beetle leaves its summer habitat and infests young plants. After 10–15 days, the females begin to lay eggs at a depth of 1–2 cm into the soil near the plants. At the experimental field of the RUE "Institute for Plant Protection," it was found that the pest population in the 4–5 leaf phase of the crop was 0.3–0.4 imago/m2, and in the 6–8 leaf phase — 0.5–1.0 imago/m2.

According to D. Spaar, Volker et al., the period from egg-laying to the emergence of the turnip sawfly false caterpillar depends on weather conditions and can average 5–12 days. Our observations have established that, under the conditions of the experimental field, this period in September 2022 and 2023 was 10–20 days, with an average daily air temperature of +11.4…+16.3 °С. By the 3–4 true leaf phase of winter winter cress, an increase in the number of false caterpillars was noted as they emerged.

Figure 1 – Dynamics of turnip sawfly population in winter winter cress crops (RUE "Institute of Plant Protection", autumn 2022–2023)

In the 5–6 true leaf phase, due to low average daily air temperatures (+4.0…+4.1 °С) in the years studied, there were 0.9–1.2 false caterpillars/plant. Upon reaching the 6–7 leaf phase of the crop, a decrease in the number of false caterpillars to 0.1–0.3 ind./plant was observed.

According to the data from route surveys conducted during the spring growing season, it was established that the agrocoenosis of winter winter cress was formed by the following species of weevils: the cabbage stem weevil (Ceutorrhynchus quadridens P.) and the cabbage seed weevil (Ceutorrhynchus assimilis P.).

The adult cabbage stem weevil is 2.5 to 3.5 mm long. The main color of the adult is black, but it looks mottled due to the unevenly distributed gray-white pubescence. A distinctive feature is the presence of a light rounded spot on the front part of the pronotum. In its life cycle, the larvae go through three stages. The first larva is 0.9 mm long, the second is 6.0 mm, and the third stage is 8.0 mm. The larval body is white and elongated, and the head is yellowish. The phytophage overwinters shallowly in the soil under leaves and other plant debris, near fields where plants of the Brassicaceae family were grown. When the soil temperature exceeds +6.0 °C, adults appear. Flight activity begins at a temperature of +12.0 °C. The peak of flight activity is reached at a temperature of +14.5 °C. Males and females have different emergence times on plants after overwintering. Males appear earlier, and females appear 10–15 days later. Females lay eggs in small groups of 2–8 eggs in the epidermis of stems and leaves. During the life cycle, one female can lay about 40–100 eggs.

According to our observations, the mass emergence of cabbage stem weevil beetles was noted in the period when the average daily air temperature fluctuated within +12.0...+14.0 °С. It was revealed that in 2022, in the Brest region, the appearance of the cabbage stem weevil (Ceutorrhynchus quadridens P.) was noted in early April, and in the Grodno and Minsk regions – in the second ten-day period of April. Under the prevailing weather conditions of 2023, the colonization of crops by the phytophage in the southern regions of the republic was noted at the beginning of the second ten-day period of March, in the central regions – at the end of the second ten-day period of April, and in the northern regions – in the third ten-day period of April.

As a result of the analysis of winter winter cress stems, it was established that their damage by cabbage stem weevil larvae in 2022–2023 was: in the northern agro-climatic zone – 67.3–59.6 %, in the central – 41.5–43.8 %, and in the southern – 33.6–40.7 %. Table 1 – Damage to winter winter cress stems by the cabbage stem weevil (route surveys)

Weighted average percentage of stem damage Year of survey by agro-climatic zones northern central southern

2022 67.3 41.5 33.6

2023 59.6 43.8 40.7

In 2022–2023, the appearance of the adult cabbage seed weevil (Ceutorrhynchus assimilis P.) in the experimental field of the RUE "Institute of Plant Protection" in winter winter cress crops was noted at the end of April – beginning of May, however, mass development began at the end of the first – beginning of the second ten-day period of May. The number of adult pests ranged from 0.8 to 4.6 beetles/25 plants in 2022 and to 0.7–5.3 beetles/25 plants in 2023.

Figure 2 – Dynamics of the adult cabbage seed weevil population in winter winter cress crops (RUE "Institute of Plant Protection", 2022–2023)

The adult phytophage is 2.5–3.0 mm long and is covered on top with dense gray scales and hairs that almost completely mask the black color of the body. The larva is 4.0–5.0 mm long, legless, slightly curved inward with a dark brown head. Beetles overwinter in the upper layers of the soil or under plant debris. In spring, at an average daily air temperature of +10 °С, adults leave their overwintering sites and additionally feed on flowering cruciferous weeds. When the air temperature reaches +13 °С, the flight of beetles is noted. The period of mass colonization of cruciferous crop fields by adults begins at a temperature of +18–20 °С. After sexual maturation and mating, the female lays mainly one egg in young pods (length from 1 to 3 cm). After 3–5 weeks of feeding, the larvae make holes with a diameter of 0.8 mm in the pod valve and go into the soil to a depth of 2–4 cm for pupation.

According to the results of the route survey in different agro-climatic zones of the republic, the number of the phytophage ranged from 2.9–4.6 beetles/25 plants (southern zone) to 3.2–4.4 beetles/25 plants (northern agro-climatic zone). In the course of the analysis of the pods, it was established that their damage by cabbage seed weevil larvae was 22.6–32.0 % in the northern agro-climatic zone, 25.0–33.1 % in the central, and 30.8–44.0 % in the southern.

The rape blossom beetle (Meligethes aeneus F.) is a widely distributed and dangerous pest in crops of cruciferous plants, including winter cress. The adult is 2.7–3.0 mm long, dark green to blue or black in color, with club-shaped antennae. At an average daily air temperature of +14 °C, the adult leaves its overwintering sites and appears on early weed cruciferous plants. Egg-laying begins 12–15 days after infestation of the crops. In late May – early June, larvae with a brown head and three pairs of legs hatch from the eggs.

Research results show that the appearance of the rape blossom beetle in winter cress crops was noted in the late stem elongation phase in 2022, and in the early budding phase in 2023. In the full budding phase during the years of the study, the density of the phytophage was 3.3–3.5 adults/plant. A subsequent decrease in the average daily air temperature to +5–7 °C during the late budding phase ensured a decrease in beetle numbers to 1.6 adults/plant.

With a further increase in temperature toward the early flowering phase of winter cress, the number of phytophage adults reached up to 2.9 individuals/plant in 2022, and up to 4.3 individuals/plant in 2023.

Figure 3 – Dynamics of the number of rape blossom beetle adults in winter cress crops (RUE "Institute of Plant Protection",

Conclusion. Monitoring of the entomological situation in the winter cress agrocenosis showed that during the autumn growing season of 2022 and 2023, the dangerous and dominant pests were the cabbage stem flea beetle (Psylliodes chrysocephalus L.) and crucifer flea beetles (undulating – Phyllotreta undulata Kutsch., blue – Ph. nigripes F., and black – Ph. atra F.), as well as the rape sawfly (Athalia rosae L.). During the spring growing season, infestation of the crops by the rape blossom beetle (Meligethes aeneus F.), cabbage seedpod weevil (Ceutorrhynchus guadridens P.), and cabbage seed weevil (Ceutorrhynchus assimilis P.) was noted.

The obtained data on the monitoring of the entomological situation will serve as a basis for assessing the harmfulness of these phytophages in winter cress crops, which will subsequently allow for the development of economically justified measures for the rational use of insecticides from different chemical classes in crop protection against pests.

• Alyapkin, A. V. Efficiency of growing winter cress in the Polesie zone / A. V. Alyapkin // Agriculture and Plant Protection. – 2006. – No. 5 (48). – P. 42–44.
• Rapeseed and winter cress: (growing, harvesting, use) / D. Shpaar [et al.]; ed. D. Shpaar. – 2nd ed., rev. and exp. – M.: [s. n.], 2007. – 320 p.
• Uteush, Yu. A. Rapeseed and winter cress in forage production / Yu. A. Uteush. – Kiev: Naukova Dumka, 1979. – 228 p.
• Milashchenko, N. Z. Technology of growing and using rapeseed and winter cress / N. Z. Milashchenko, V. F. Abramov. – M.: Agropromizdat, 1989. – 223 p.
• Plant growing. Field practice: textbook / D. I. Melnichuk [et al.]; ed. D. I. Melnichuk. – Minsk: ICT of the Ministry of Finance, 2013. – 304 p.
• Methodological guidelines for registration trials of insecticides, acaricides, molluscicides, rodenticides, and pheromones in agriculture / Scientific and Practical Center of the NAS of Belarus for Agriculture, Institute of Plant Protection; ed. L. I. Trepashko. – Priluki village, Minsk region: [s. n.], 2009. – 320 p.
• Dospekhov, B. A. Methodology of field experiments (with the basics of statistical processing of research results): textbook / B. A. Dospekhov. – 5th ed., rev. and exp. – M.: Agropromizdat, 1985. – 351 p.
• Volker, H. P. Rapeseed: diseases, pests, weeds / H. P. Volker. – Minsk: Divimedia, 2012. – 196 p.
• Integrated protection systems for winter and spring rapeseed against pests, diseases, and weeds: (recommendations) / S. V. Soroka [et al.]; Scientific and Practical Center of the NAS of Belarus for Agriculture, Institute of Plant Protection. – Minsk: Colorgrad, 2016. – 124 p.
• Monitoring of pests and diseases of agricultural crops: study guide / S. V. Stankevich, I. V. Zabrodina [et al.]; Ministry of Education and Science of Ukraine, Kharkiv National Agrarian University named after V. V. Dokuchaev. – Kharkiv: FOP Brovin O. V., 2020. – 624 p.

S. A. Gaidarova, A. A. Zaprudsky, D. F. Privalov RUE «Institute of Plant Protection», Priluki, Minsk region

DYNAMICS OF THE NUMBER OF DOMINANT SPECIES OF PESTS IN AGROCENOSIS OF COMMON

Annotation. The paper presents the assessment data on entomological situation in agrocenosis of common winter cress. It was identified that during the autumn vegetation period in 2022–2023 the dominant pests were cabbage flea beetles (Psylliodes chrysocephalus L.) and crucifer flea beetles (undulating – Phyllotreta undulata Kutsch., blue – Ph. nigripes F. and black – Ph. atra F.) as well was rape sawfly (Athalia rosae L.).

During the spring vegetation period in 2022–2023 a high infestation of winter rape crops was observed. Data on pests are presented in the table:

The damage to crop stems caused by the cabbage stem weevil (Ceutorrhynchus guadridens P) reaches 59.6–67.3 % in the republic.

Key words: common winter cress, monitoring, pests, prevalence, damage.