Species ratio in the complex of the cruciferous bugs and seasonal dynamics of the population number

Abstract

The complex of cruciferous bugs includes such species as painted or harlequin (cabbage) bug (Eurydema ventralis Kol), pentatomid rape bug (E. oleraracea L.), and mustard bug (E. ornata L.). They belong to a line Hemiptera, the family Shield bugs (Pentatomidae), and the genus Cruciferous bugs (Eurydema). The dominant species is the cabbage bug. The mustard bug dominated only in 2007, and since 2012 it has not been detected in the records. They are widespread throughout the whole territory of Ukraine. Both adult bugs and larvae damage the crops; they pierce the leaf skin or floriferous shoots with the proboscis and suck out the juice. The light spots appear at the puncture points, the tissue dies, falls out, and the irregular form holes are formed. When the seeds are damaged, the flowers and ovary fall off, and the seeds' quality deteriorates. The harmfulness of the bugs increases dramatically in dry and hot weather. We found out that the largest number of wintering bugs was concentrated in the forest belts, near which there were the crops of spring oilseeds and cabbage plants and the seeds of white cabbage. The density of wintering imagines of the cabbage bug was 1.7–4.4 specimens/m², and the density of the rape bug was 0.9–2.3 specimens/m² of the forest floor. In the first turn, the wintered bugs' imagines populated the cabbage seeds as a trap crop, and then they populated the sprouts of spring rape and mustard. The density of the cruciferous bugs on the seeds of white cabbage of Kharkivska 105 variety was 19.0-30.7 specimens per plant at the beginning of the populating of spring oilseed cabbage crops at the Educational, Research and Production Centre "Research Field" of Kharkiv National Agrarian University named after V.V. Dokuchaiev (Ukraine). The maximum density of the cruciferous bugs in the phenophase of the yellow bud on the crops of spring oilseed cabbage plants was the following: 4.5±1.45 specimens/m² of the cabbage bug was found on spring rape of Ataman variety, 4.0±1.83 specimens/m² on white mustard of Carolina variety and 3.5±2.65 specimens/m² on Chinese mustard of Tavrychanka variety; and the density of the rape bug was 0.7±0.23, 0.5±0.23 and 0.5±0.3 specimens/m² respectively. The maximum density of the cruciferous bugs in the phenophase of the yellow bud on spring rape of Ataman variety was 6.0±0.9 specimens/m², on white mustard of Carolina variety it was 5.7±0.85, on Chinese mustard of Tavrychanka variety, the average density was 5.3±0.9 specimens/m² at the state enterprise "Research Farm "Elitne" (Ukraine). The highest number of cabbage and rape bugs at a density of 22.3–30.7 specimens/plant is concentrated on the seeds of white cabbage plants at noon, and the lowest number of them was found at 8.00 AM, and the density was 17.9–28.5 specimens/plant. The maximum density of 51-60 specimens/plant was at noon. We found out that the beginning of populating spring rape of Ataman variety by the bugs that occurred in the phenophases of 3−4 pairs of true leaves, namely during the rosette formation. The larval reappearance's beginning took place when the sum of the active temperatures was 520–688 °C (from the end of the third decade of April to the beginning of May's third decade when the sum of the active temperatures was 106-412 °C). We observed the peak of the cruciferous bugs' number from the second and third decades of June to the third decade of July, depending on the year's climatic conditions. The highest density of the bugs was observed before harvesting.