THE DIVERSITY OF USEFUL ARTHROPODS IN TWO WHEAT AGROECOSYSTEMS FROM TRANSYLVANIAN PLAIN

. The increase in agricultural production is conditioned by several factors, among which plant protection against pests plays a very important role. Alongside chemical methods, biological control methods against harmful organisms in crops have recently become widespread


INTRODUCTION
Wheat is one of the oldest cultivated plants and the most important food plant, with wheat flour bread constituting the basic food for a large part of the world's population (Muntean et. al., 2008).Wheat grains are used as raw material for various industrial products such as starch, gluten, or ethyl alcohol, and also for the production of pasta, semolina, glucose, but primarily for making flour, which is used for bread making, this staple food providing approximately 20% of the total calories consumed by humans (Muntean et al., 2003).
Wheat is the host and therefore the preferred food for most species of specific pests of cereal crops.The evolution of wheat pests is influenced by the ecological conditions in the wheat fields (Malschi, 2007) There are more than 100 species of harmful arthropods that attack wheat, of which about 64 are occasional or do not live near wheat fields, and about 65 species present economic importance (Bajwa et al., 2020).
Pest control in agricultural crops is achieved through several methods: chemical (using pesticides), biological (using antagonistic organisms and natural products), genetic (improving plant resistance to harmful organisms), agronomic (through soil work, including weeding) and physico-mechanical (thermal disinfection of seeds, plant surgery, seed scarification, etc.) (http://www.icpa.ro).
The implications resulting from the irrational application of pesticides have led to the emergence of resistant forms of phytosanitary agents, at least 20 major aphid pest species worldwide have developed resistance to at least one insecticide (cypermethrin, lambda-cyhalothrin, acetamiprid, thiametoxam, imidacloprid, etc.), further increasing the impact of harmful organisms, as well as causing more intense pollution of the environment (Bass and Nauen, 2023).Therefore, specialists in the field of plant protection have considered necessary to develop a more environmentally friendly strategy to combat harmful organisms, which has crystallized under the name of integrated protection (Voloşciuc, 2014).Some authors (Hemidi et. al., 2020 andMalschi, 2003), state that in the face of observed ecological disturbances, the best strategy for sustainable agriculture is biological control, as it has economic and ecological advantages.In applied entomology, auxiliary entomophages used in biological control of pests are grouped into two categories: predators and parasites.Also, in more studies (Moreno et al., 2010;Santra, 2014;Mukherjee et. al., 2020), is suggested that the success of integrated pest management may depend on the identification and use of the most abundant natural enemies of these pests, as well as the least abundant, and the elimination of these insects leads to the decline of biodiversity.
According to some authors (Eilenberg et. al., 2001;Van Lenteren, 2012), biological control is define as the use of living organisms to suppress the population of a certain harmful organism, making it less abundant or less harmful than it would otherwise be.
In this paper, we aimed to study the useful entomofauna in two cereal agrobiocenoses from the Transylvanian Plateau, as well as the impact of insecticide treatments on useful arthropods.

MATERIAL AND METHODS
Given the importance of the useful arthropod fauna in limiting wheat pests, during 2016-2018, its monitoring was carried out at the autumn wheat culture, in two locations, within the Agricultural Research and Development Station (ARDS) Turda (Cluj dept., Romania).
In addition to the land and experimental fields it owns, the ARDS Turda is the beneficiary of a farm for field crops arranged in an anti-erosion system and surrounded by agroforestry shelterbelts (Bolduț farm), these two locations are quite close in terms of distance (figure 1).

Figure 1. https://www.google.com/maps
Consequently, the research was conducted in two agroecosystems: at Turda in open field conditions and at Bolduț in fields with agroforestry shelterbelts, for the wheat culture.The research was organized in two variants, placed in large plots of 0.5 hectares.In the first experimental variant, no insecticides were applied, while in the second variant, insecticides were applied at two specific moments: at the end of tillering concurrent with herbicide application, and in the phenophase from the appearance of the boot until the emergence of the ear (table 1).The collection of useful insects was carried out every ten days using an entomological net through 100 double sweeps for each sample, starting from the spring months until harvest, depending on climatic conditions (collections were made only on days without rain or wind).
Species of entomophagous insects were identified based on morphological, biological, and geographical criteria (Malschi, 2007), and a series of ecological indices (Stan, 1995) were calculated: Shannon-Weaver Diversity Index (H) highlights the differences between two samples and considers both the abundance and evenness of species distribution, calculated using the formula: Jaccard Similarity Coefficient represents the affinity of species, i.e., the extent to which two populations, biocenoses, habitats, or ecosystems are similar to each other, calculated using the formula: where: a= the number of species in ecosystem , b= the number of species in ecosystem 2, c= the number of common species in ecosystems 1 and 2.
After collection, the samples were refrigerated, and after a few days the species of useful arthropods present in the two agroecosystems were identified.Biodiversity indices represent the mathematical measure of species diversity in a community, and through the ecological indices used, we can compare the structure of some communities from the point of view of biodiversity (Popov et al., 2009).

RESULTS AND DISCUSSIONS
From the climatic data presented in Table 2, it can be observed that in two of the three years, namely 2015 and 2017, the autumn months were predominantly warm.Similarly, in the winter months, there were mostly positive deviations compared to the multi-year average, suggesting a positive trend in winter temperatures.The tendency for temperatures to rise compared to the multi-year average was also noticeable in the spring and summer months.
The autumns of the years in which the experiments were conducted recorded a generally rainy pluviometric regime, which positively influenced the germination and emergence of wheat plants.Springs started with two very rainy months, March and April, in all three years (Table 3).The fluctuation in the number of predatory and parasitic insects as a component part of agrobiocenoses is closely related to the locality and the climatic conditions of the years, which can be observed from the data presented in Table 4.Moreover, in other studies conducted in our country (Popov, 1980;Popov et. al., 2005;Popov et al., 2006;Malschi et. al., 1997;Malschi, 2003), it is emphasized that entomophagous constitute a distinct group, their population dynamics being in accordance with the abundance of food sources (harmful arthropods), but also with the characteristics of the experimental area.According to these statements, it can be observed that the total number of individuals captured shows significant variability both from one year to another and between the two agroecosystems.It is important to mention that the data presented in Table 4 refer only to the dynamics of entomophaghous populations in the two agroecosystems in the variants untreated with insecticides.
The more favorable influence of agroforestry shelterbelts in ensuring very conducive areas for the development of entomophaghous populations is evident, an influence reflected in the significantly higher number of captures recorded at Bolduț compared to those at Turda.The most pronounced differences between the two agrobiocenoses are recorded in the year 2018, namely a considerable increase of 608 individuals for the agroecosystem at Bolduț.In other years, the differences are smaller, being only 100 individuals in 2016 and 229 individuals in 2017.
Terracing the land and arranging agroforestry shelterbelts have been important measures in reducing soil erosion.Over time, these forest belts have led to a positive evolution and the stability of these agroecosystems by protecting entomophagous insects which play an active role in regulating this balance.Therefore, multi-year research conducted has demonstrated the efficiency of agroforestry shelterbelts in the fight against pests and their massive invasions by naturally increasing the arthropod fauna number (Malschi, 1995;Malschi et. al., 1998;Malschi et. al., 1999;Malschi, 2003;Malschi et. al., 2010).
The biodiversity parameters used for the mathematical quantification of species diversity in the two biocenoses are differentiated.The possibility that two individuals randomly selected from a sample belong to different species, or the values of the Shannon index, do not show significant differences between the two agroecosystems, but still, at Bolduț the thresholds of this indicator are slightly higher than those at Turda in all three years.The Simpson diversity index, a synthetic parameter of diversity that encompasses both abundance and the number of individuals, suggests through its values a slight dominance of entomophagous diversity in the agroforestry system at Bolduț compared to that at Turda (Table 4).
Also, the relative abundance of species characterized by another index, namely equitability, reflects a quite pronounced similarity regarding the abundance of entomophagous in the two agroecosystems.Moreover, the Jaccard similarity index highlights a fairly pronounced affinity regarding the diversity of useful insects between the two agroecosystems.The quite close values of this parameter over the three years suggest a quite pronounced stability of the diversity of entomophagous in the two biocenoses (Table 4).The annual evolution of entomophagous insects in the two cereal agroecosystems, in the variants treated with insecticides at two different application times, is presented in Table 5.The significant numerical variation of useful arthropods from one year to another within the same ecosystem (both untreated and treated) reflects the active role of the environment in the recovery of arthropod numbers.Therefore, the annual monitoring of entomophagous populations becomes crucial in making the most relevant decisions regarding integrated pest management.Furthermore, when comparing the total number of individuals from treated and untreated variants (Tables 4 and 5), a pronounced reduction in the numerical component is observed when treatments are applied.The Shannon index reflects a greater impact of treatments on the diversity of useful arthropods in the Turda agroecosystem compared to that of Bolduț.Another mathematical parameter of diversity, the Simpson index, shows a similar tendency to that of the Shannon parameter at both locations, in the sense that, over all three years, the values of these two parameters are higher in the Bolduț agroecosystem.In the case of equitability, it seems that even in the variant where insecticide treatments were applied, useful arthropods shows a rather pronounced similarity at both locations, with the smallest differences being 0.21 in the year 2016.If the value parameters of variability for beneficial arthropods are compared, it can be observed from Tables 4 and 5 that these register higher values in the conditions where insecticides were not applied, compared to the variant where treatments were carried out.The superior variation of useful arthropod in the absence of insecticide application is recorded in all three experimental years and for both agroecosystems.
Moreover, the application of treatments causes disturbances also at the level of entomophagous common to both biocenoses, a fact reflected in the differentiated values of the Jaccard coefficient in the two variants, treated and untreated.In all three experimental years, the Jaccard coefficient has considerably higher values in the untreated variant compared to the treated one.
Among the groups of entomophagous insects identified during 2016-2018 in the ARDS Turda area, the order Coleoptera is included, being the most numerous and widespread group of insects globally (about 400,000 globally and over 7500 in Romanian fauna), and the analysis of beetle fauna is essential for biological research (Niţu, 2007;Roșca et. al., 2011).Among the captured zoophagous Coleoptera, the species Cantharis fusca L. is the best represented in terms of the average over the three years of experimentation (Tables 1 and 2).Laboratory research (Malschi, 2007) demonstrates their effectiveness in limiting some wheat pests, as they feed on aphids or thrips.Soldier beetles (Cantharis fusca) are abundant and widely distributed across all terrestrial soils, being considered polyphagous predators (Traugott, 2001).Cantharid larvae have been observed feeding on snails, and adult beetles have been seen preying on aphids and other invertebrates (Traugott, 2003).
Coccinella septempunctata L. is found in all cultures, but also on spontaneous flora, wherever there is aphid infestation, playing a significant role in reducing these pests' populations (Roșca et. al., 2011).Regarding the evolution of the species Coccinella 7-punctata, it can be said that it has a fairly uniform distribution over the three years of experimentation for the Turda agrobiocenosis, but their number is higher for the Bolduț agrobiocenosis.
The order Hemiptera does not have a significant spread among the entomophages of the two agrobiocenoses, except for the species Nabis ferus L., which in the last two years of experimentation has recorded a significant but quite variable appearance.Predatory Nabidae are spread in various biotopes, playing a special role in the main agricultural agroecosystems (soy, cotton, alfalfa, tobacco, wheat, etc.) (Roșca et. al., 2011).
In a study (Veríssimo et. al., 2020) it was noticed predators of the family Syrphidae (Insecta: Diptera) are among the most abundant natural enemies in pastures in Southeast Brazil.Since some Syrphidae species are migratory, it is necessary to consider protecting them in their natural habitats, being polyphagous and very fertile (they reproduce quite quickly).It is also important to protect the areas where they hibernate, such as bushes, brambles, etc., located near agricultural areas (Ciochia, 1997).From the data presented above, we can see the higher number of entomophages from the Syrphidae family in the agroecosystem with protective agroforestry belts, again highlighting their important role in protecting and developing the natural stock of entomophagous.
In the world of insects, parasitism is a complex phenomenon, in which the host and the parasite are in a continuous interrelationship, and the dependence of the parasite on the host is a necessary biological process because no parasite can develop outside it (Lăcătușu, 1975).A study conducted in China specifies that Aphidius avenae Haliday and Aphidius gifuensis Ashmead (Hymenoptera: Braconidae), accounted for about 48% of the total natural enemies in autumn wheat fields in China, these two species being dominant parasitoids in suppressing the growth of the Sitobion avenae F. (Hemiptera: Aphididae) population (Yingjie et. al., 2016;Wang et. al., 2008).From the results of our research, parasites from the order Hymenoptera, including the species Aphidius avenae H., are present in wheat crops in the ARDS Turda area in a high number.
Based on the decennial and ultimately annual collections, it can be seen that the species of the Araneae group show an upward trend over the three years in both biocenoses.An aspect worth mentioning is that the numerical values from the two biocenoses are differentiated at significant thresholds with favorability for the Bolduț agrobiocenosis.The share of spiders in the total captured entomophagous is 46% in Turda and 40% in Bolduț.Spiders belong to the class of Arachnids and are distributed almost all over the globe.They are found in most ecosystems, the species included in this order being the most numerous group (Roșca et. al., 2011).

CONCLUSIONS
Biodiversity parameters (Shanon, Simpson, Evenness, and Jaccard), used for the mathematical quantification of species diversity in the two biocenoses, suggest the existence of slightly higher biodiversity in the Bolduț agroecosystem, which recommends the favorability of agroforestry belts in protecting useful entomofauna.
The most widespread group of entomophagous caught in both agroecosystems is that of Spiders, followed by parasites of the order Hymenopterae.The share of spiders in the total entomophagous captured is 46% in Turda and 40% in Bolduț, hymenoptera being present in proportion of 21% in Turda and 31% in Bolduț.
In the variant treated with insecticides at the two moments of application, the number of entomophagous captured is lower.In 2016, 94 individuals were collected in Turda and 264 in Bolduț.In 2017 the number of useful arthropods collected in Turda was 318, and in Bolduț 525, and in 2018, 543 individuals were captured in Turda and 885 in Bolduț.
The conducted research has highlighted that the application of insecticide significantly reduces the population of useful arthropod, a population that subsequently begins to recover at a rate closely linked to the characteristics of the agrobiocenosis and the climatic conditions.Chemical treatments applied only upon warning do not irreversibly reduce the population of useful insects, both in terms of number and diversity.

Figure 2 . 3 .
Figure 2. Experimental field Turda Figure 3. Experimental field Bolduț The biological material used was the wheat variety 'Andrada', a variety developed at the Agricultural Research and Development Station Turda.The collection of useful insects was carried out every ten days using an entomological net through 100 double sweeps for each sample, starting from the spring months until harvest, depending on climatic conditions (collections were made only on days without rain or wind).Species of entomophagous insects were identified based on morphological, biological, and geographical criteria(Malschi, 2007), and a series of ecological indices (Stan, 1995) were calculated:Shannon-Weaver Diversity Index (H) highlights the differences between two samples and considers both the abundance and evenness of species distribution, calculated using the formula: where: H= diversity, ni= the number of individuals of each species, i= 1, 2, 3,..., n species, N= the total number of individualsEquitability (E) represents the uniformity of the distribution of individuals across species and is calculated as: diversity, S= the number of species in the examined culture Simpson's Diversity Index (IS) is used in entomology to describe the diversity of a biocoenosis and is calculated using the formula: the number of individuals of each species, N= the total number of individuals.