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Abstract
Shelterbelts contribute to the ecological value of agricultural lands and the balance of biogeocoenoses, including faunal biodiversity. Studies on complex of insect species in shelterbelts are based on the concepts of forest and agricultural biocoenoses interaction. Age, stand height, composition, and design features are the criteria of a shelterbelt which have a significant impact on the insect species composition and theirbdispersal within the shelterbelts. Forestry characteristics of shelterbelts, their species composition and health are indicators of both a specific habitat of certain insect species and formation of appropriate entomocomplex in them.
Materials and Methods
The shelterbelts located on the territory of the State Enterprise “Elitne Research Farm of Plant Production Institute named after V. Ya. Yuryev of NAAS” (Kharkiv Region) were studied in 2018–2019. Field studies were conducted during the growing season using generally accepted entomological and silvicultural methods. The number of tree rows, the stand height, and the type of shelterbelt design were determined at each study plot. The occurrence of a particular insect species was estimated as a percentage (%) of the studied sites where a particular insect species was identified. Leaf population was defined as the proportion (%) of damage from the total crown.
Results
Oak shelterbelts with different species composition had mainly a dense structure. The main tree species that were examined during the research were: green ash (F. lanceolata L.) – 45%; English oak (Quercus robur L.) – 26%, Norway maple (Acer platanoides L.) – 25%, and European ash (Fraxinus excelsior L.) – 4%. Tatar maple (A. tataricum L.) and Siberian pea shrub (Caragana arborescens Lam.) grew from undergrowth species which were observed in all shelterbelts studied in the amelioration system in the State Enterprise “Elitne Research Farm of Plant Production Institute named after V. Ya. Yuryev of NAAS”.
The study showed that shelterbelts had weakened and severely weakened health (health condition index of the shelterbelts varied from ІІ,1 to ІІІ,0).
During the analysis of the shelterbelt health, considering the species composition in the stand, it was found that maple trees had the best health, namely the health condition index was within I,0–II,8 points, but only if they made a small proportion in the stand (up to 5% of shelterbelt 7). In shelterbelts 15, 11, and 38, the health condition indices of oak were 2–5% lower than the average health index of all trees in the stand (Fcrit = 31.2; Ft = 3.9; p ? 0.05). Only in shelterbelts 7 and 23 the health of oak was better by 19–50% compared to other species (Fcrit = 56.1; Ft = 3.9; p ? 0.05). The dominance of maple in the stand reduces the overall resilience of trees in the shelterbelt; the tree health in the shelterbelt varies within the III–IV health condition categories.
The entomological analysis of the main forest-forming species in the shelterbelts helped identify 45 species of insects from 32 genera and 13 families which belong to three series: Coleoptera, Lepidoptera, and Hymenoptera.
The identified species belong to two groups: xylophage insects (23 species) – their development occurs under the bark or in the upper layer of tree trunks, branches or stumps, and phyllophagous insects (22 species) – development and nutrition take place on the leaf blade.
The insects which occurred infrequently had a predominant proportion, namely– 43.2%, the percentages of mass and common species were 25% and 22.7 % respectively; 9.1% of species occurred singly.
The most common of the Curculionidae were Hylesinus toranio and Scolytus intricatus, whose damage was noted under the bark of trunks and branches of ash and oak.
During the study of the shelterbelts in the first decade of May over the trees of European ash, a mass flight of adults Tomostethus nigritus was recorded, and in early June, Macrophya punctumalbum, but when inspecting the damaged crown, it was dominated by larvae of Tomostethus nigritus.
During the season, two species of insects from the nut-forming family were identified on the leaf plate of English oak trees. Among them, Diplolepis quercusfolii was common and Neuroterus numismalis occurred rarely.
From the gall wasps family, two species from the family Diplolepis quercusfolii and Neuroterus numismalis respectively occurred occasionally and singly on the leaf blade of oak trees.
The observations helped detect numerous injuries of trees in the stands caused by various factors. The cumulative effect to some extent brought about a partial drying of trees in the shelterbelt, which, in turn, favoured expanding of the foci of pathogens and pests which inhabited individual trees in the shelterbelt. Lack of forestry care in the studied shelterbelts led to a significant reduction in their viability and weakening of their protective functions.
Conclusions
The worst health condition in the shelterbelts was observed in European ash – IV,1 and green ash – III,6. Norway maple had health condition index of III,9 which is related to a significant drying of the crowns, probably with verticillium wilt. The best health was distinguished in maple trees – their health condition index varied within I,0–II,8 points, but only when having an insignificant proportion in the stand. The dominance of maple in the stand led to a decline of the overall resilience of the stand (health condition index ranged within III,9– IV,1).
We found 45 species of insects from 32 genera and 13 families in the shelterbelt. Of these, xylophage insects are represented by 23 species and phyllophagous insects by 22 species. In general, 43.2% occurred rarely, 25% and 22.7% were mass and common species respectively, and 9.1% of species occurred singly.
The study established that due to the lack of forestry and reclamation interventions in the shelterbelts, conditions for the rapid development of many phytophages had been created, in particular for Chrysomelidae insects. Accumulation of a large number of weakened maple trees creates favourable conditions for a mass reproduction of xylophagous insects.
It was revealed that in the shelterbelt system of the State Enterprise “Elitne Research Farm of Plant Production Institute named after V. Ya. Yuryev of NAAS” a typical for agrolandscapes entomocomplex was formed at this location, which did not depend on the differences in forestry and reclamation indicators of shelterbelts.
2 Figs., 2 Table, 26 Refs.
Key words: health condition index, xylophagous insects, philophagous insects.