Nutritional indices and feeding preference of the Plutella xylostella L. (Lepidoptera: Yponomeutidae) in several Brassicaceae plants

The quantity and quality of food consumed by insects affect their growth, development; likewise, the diamondback moth Plutella xylostella (Lepidoptera: Yponomeutidae), one of the important pests of Brassicaceae plants. The study aimed to determine feed preferences and the effect of four Brassicaceae, namely cabbage (Brassica oleracea var. capitata), caisin (B. rapa), broccoli (B. oleracea var. italica), and Rorippa indica, on the nutritional indices of P. xylostella larvae. The research methods consisted of insect rearing, nutrition indices test, preference test, and proximate analysis. The results showed that the highest preference was found in R. indica (47.81%), while the other three plant species were not significantly different. Cabbage treatment showed the highest efficiency of conversion of ingested food (ECI) (8.56%), followed by R. indica, caisin, and broccoli. The same thing, cabbage treatment showed the highest efficiency of conversion of digested food (ECD) (13.02%), followed by caisin, R. indica, and broccoli. Broccoli had the highest approximate digestibility (AD) (89.38%), followed by R. indica, cabbage, and caisin. In general, the results of the nutritional indices showed that cabbage was the most suitable feed for P. xylostella larvae; in addition, with a high feeding preference, R. indica could potentially be used as a trap crop.

Irrigated trap crops impact key hemipteran pests in organic pistachio orchard

Using sown groundcovers as trap crops to protect a cash crop is a traditional pest management tool. Pistachio is a major crop in California’s Central Valley, where high summer temperatures and little to no precipitation between May and November lead to summer dry-down of annual groundcover. Hemipteran pests that consist of ‘small bugs’ and ‘large bugs’ are a major contributor to nut damage, especially in organic production. In this 2-year field study, we tested the use of irrigated trap crop mixtures, sown between tree rows, to reduce those hemipteran pests’ abundance or damage. Biweekly beat samples of the tree canopy and sweep samples of the sown groundcovers in trap crop plots and resident weedy vegetation in control plots were taken over two consecutive growing seasons. Arthropod richness and abundance were highest in the groundcover and tree canopy in the trap crop plots. Small and large bug pest populations were higher and lower, respectively, in the tree canopy in trap crop plots, indicating a mixed response of these hemipterans to the presence of the trap crops. Additionally, natural enemy populations were more abundant in the tree canopy in trap crop plots than in control plots. There was no difference in nut damage between plots with and without the trap crop. These findings suggest that populations of hemipteran pests and beneficials can be manipulated successfully with irrigated trap crops, but future studies will need to focus on doing so in a way that decreases hemipteran pistachio damage.

Elucidating the Fitness of a Dead-End Trap Crop Strategy against the Tomato Fruitworm, Helicoverpa armigera

Solanum viarum has been proposed as a potential dead-end trap crop for the management of Helicoverpa armigera because of its unsuitability for larval growth and survival despite being overwhelmingly preferred for oviposition. This study delved into the different S. viarum accessions for ovipositional preference and non-suitability for larval growth and survival of H. armigera. Besides, foliage trichomes, acylsugars, and phenolic content of S. viarum plants were assessed and compared with tomato. Since there is no significant variation in the ovipositional preference and larval performance of H. armigera, our result revealed that all those evaluated accessions of S. viarum have the potential to be used as a dead-end trap crop for the management of H. armigera. However, significant variation among the S. viarum accessions in terms of H. armigera oviposition was also evident in a no-choice experiment. Because of high-density glandular trichomes, acylsugars, and phenolic content, S. viarum significantly impaired H. armigera larval growth and survival compared to the tomato. Hence, our study elucidated that the S. viarum plant fits with the criteria for dead-end trap crop, and has the potential as a dead-end trap crop for the H. armigera, which needs to be tested under large, open-field conditions.

Effect of steroidal glycoalkaloids on hatch and reproduction of the potato cyst nematode Globodera pallida

Steroidal glycoalkaloids (SGAs) are phytoanticipins found in solanaceous crops that act as the first line of chemical defense against pathogen attacks. Solanum sisymbriifolium, a trap crop for potato cyst nematodes, has been shown to effectively reduce populations of Globodera pallida. Solanum sisymbriifolium contains α- solamargine and other solasodine type glycoalkaloids that may contribute to plant defenses. The current study evaluated the influence of solanaceous SGAs on G. pallida hatch, development, and reproduction. Exposure to α- solamargine and α- solamarine reduced G. pallida hatch by 65 % and 87 % respectively. Exposure of G. pallida cysts with the glycoalkaloids α- solamargine and solasodine significantly reduced infection in susceptible potato Russet Burbank by 98 and 94 % compared to the control. Exposure of cysts to either solasodine or solamargine significantly reduced reproduction of G. pallida on Russet Burbank by 99 % compared to the control. The study demonstrated the deleterious effect of SGAs on G. pallida hatch, infection, and reproduction.

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

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.

Control of Meloidogyne graminicola a Root-Knot Nematode Using Rice Plants as Trap Crops: Preliminary Results

Meloidogyne graminicola is one of the most harmful organisms in rice cultivation throughout the world. This pest was detected for the first time in mainland Europe (Northern Italy) in 2016 and was subsequently added to the EPPO Alert List. To date, few methods are available for the control of M. graminicola and new solutions are required. In 2019, field trials using rice plants as trap crops were performed in a Lombardy region rice field where five plots for three different management approaches were staked out: (i) Uncultivated; (ii) Treated: three separate cycles of rice production where plants were sown and destroyed each time at the second leaf stage; (iii) Control: rice was sown and left to grow until the end of the three cycles in treated plots. The results showed that in the treated plots, the nematode density and the root gall index were lower than for the other two management approaches. Moreover, the plant population density and rice plant growth were higher than the uncultivated and control plots. In conclusion, the use of the trap crop technique for the control of M. graminicola gave good results and thus it could be a new phytosanitary measure to control this pest in rice crop areas.