As a modern orchard management tool, vegetative ground cover can increase biodiversity, enhance the effect of natural enemies, and reduce the amounts of chemical agents used to control pests. This study aimed to investigate the temporal niche relationship between pests and natural enemies in peach orchards (1) planted with flowering plants as a ground cover or (2) with naturally occurring vegetative ground cover or (3) plowed, with the objective of clarifying the conservation effect of peach orchard ground cover on different natural enemies. The results showed that the niche width value of natural enemies in peach orchards planted with the flowering plants was the highest, followed by natural vegetation peach orchards. The ladybird beetle (Coccinellidae) ecological niche width values were the highest in the natural enemy communities of the two types of peach orchards. These results demonstrate that vegetative ground cover in peach orchards can effectively harbor natural enemies and that coccinellids are highly adapted for the ecological environment of the peach orchard.
Fruit tree cultivation occupies an important position in the world’s agricultural economic status and development. Fruit trees planted in China are predominantly apple (Malus pumila Miller), pear (Pyrus sorotina L.), and peach (Amygdalus persica L.) (Dong et al. 2022). Peach is planted on 851,700 ha in China, ranking first in the world (Wang 2021). The excessive use of chemical pesticides has become one of the major problems faced by the peach industry. Although chemical insecticides can effectively and quickly control peach tree pests, they cause such problems as development of pest resistance and fruit quality degradation (Camila et al. 2016, Gurr et al. 2017). Moreover, most insecticides have toxic effects on natural enemies, thereby reducing their impact and seriously affecting the ecological balance with agroecosystems in peach orchards (Gardner et al. 2011, Wang et al. 2019).
Biological control using natural enemies in orchards is ecologically compatible and safe for nontargets, and it provides sustainable pest control in these perennial systems. For example, horticultural vegetation cultivation can greatly increase the variety and numbers of natural enemies in orchards (You et al. 2019). This production mode can also increase the spatial niche overlap and temporal niche width of natural enemies and further enhance their impact in pest management (Jiang et al. 2011, Wyss et al. 2009). It is therefore important to understand the spatiotemporal niches of major pests and natural enemies of vegetation growing in peach orchards for biological pest control (Gardner et al. 2011, Lv et al. 2008).
In this study, three different types of ground covers in peach orchards—planted with flowering plants, naturally occurring vegetation, and plowed area—were compared with respect to the ecological niche indices of pests and natural enemies. Our objective was to define the temporal and spatial synchronization between these niches and to clarify the conservation effect of different peach orchard ground cover patterns for natural enemies.
Materials and Methods
The orchard selected for this study was located on the Baiguoyuan Family Farm in Qufu City, Shandong Province, China, which has an area of approximately 22 ha in orchards. The peach orchard sampled measured 85,600 m2 in total area, and the trees were mainly medium- and late-maturing varieties that were 5–9 yr old planted at a spacing 3 × 4 m. The three treatments were planted vegetation, natural vegetation, and plowed areas with an area of 12,000–15,000 m2 for each treatment. Three repetitions were set up for each treatment, with an area of 4,000 m2 per repetition.
In the planted vegetation treatments, two rows (0.8–1.0-m row spacing) of hairy vetch (Vicia villosa Roth) were sown at a rate of 2 kg of seed per 667 m2 between the rows of peach trees in early October 2018. In early April 2019, the vetch began to flower and continued to flower until early June, after which the seeds matured and the vegetation wilted, providing for overwinter seedlings without replanting. From April to July every year, a small number of flowering plants, such as marigolds (Tagetes erecta L. and Tagetes patula L.) were planted in these treatment areas. By the third year, most of the ground was covered, resulting in a stable flowering plant community. Some natural weeds, including green bristlegrass [Setaria viridis (L.) Beauverd], common crabgrass [Digitaria sanguinalis (L.) Scopoli], rattail fescue [Vulpia myuros (L.) Levin], and chickweed [Stellaria media (L.) Villars] were retained in the ground cover.
In the natural vegetative area, weeds with high stalks and deep roots that compete with peach trees for fertilizer and water were manually removed in early April. Naturally occurring weeds with less water and fertilizer consumption, including S. viridis, D. sanguinalis, V. myuros, and S. media, were retained. Natural weeds were machine mowed two to three times a year, with a stubble height of approximately 10 cm and a weed height of approximately 40 cm. After 3 yr of continuous optimization, a natural weed ground cover was formed.
In the plowed area, all weeds were manually removed in early April, and the height of the weeds was maintained below 5 cm by machine cutting in the later stage. The cut weeds were not left in the experimental area. The machine was used to cut weeds four to five times per year.
All treatment areas were managed for control of major diseases and insect pests. The chemicals used included phenoxymethanazole, pyrimethanil, fluosilazole, pentazol, pyrazole, pyrazone, spironethyl ester, chlorfenazamide, and methylurea. The areas were sprayed five to six times a year according to standard recommendations.
Populations of natural enemies and insect pests were sampled every 10 d from April to November (one growing season) in 2021 and 2022. The obtained insects were identified according to their morphological characteristics to the family level by insect taxonomy researchers in our institution. The main pest targets were Aphidoidea, Cicadellidae, and Pentatomidae, whereas targeted natural enemies were Coccinellidae, Chrysopidae, parasitic wasps, Syrphidae, and Araneida. A visual observation method based on five-site sampling and yellow sticky traps was used to sample tree pests and natural enemies. A sweep net method based on five-site sampling was used to sample pests and natural enemies in the ground cover. Each sampling method was repeated three times at each sampling site.
In sampling the trees, five sampling sites were selected in each treatment area and two trees were sampled at each of those sites. One large lateral branch was selected on each tree on the east, south, west, and north cardinal directions of the tree. The species, number of pests, and natural enemies on each lateral branch were visually observed. In total, 50 trees with 200 lateral branches were surveyed in each treatment area. Yellow sticky traps also were used to sample pests and natural enemies on the trees. Fifteen sampling sites in each treatment area were selected to hang yellow sticky traps. The number of parasitic wasps on each trap was determined.
Fifteen sample sites, approximately 10 m in length, were selected on the vegetation between the rows of peach trees or around them, and a standard sweep net was swept as close to the ground as possible. Each site was continuously swept 20 times. Species and number of the most numerous natural enemies captured were recorded.
Temporal niche of pests and natural enemies in peaches with planted vegetative ground cover
The pest group with the largest temporal niche width was the Cicadellidae with 0.663, and the Coccinellidae exhibited the largest temporal niche width among the natural enemies with 0.691 in the ground cover, followed by Coccinellidae (0.670) and Chrysopidae (0.677) sampled from the trees. The largest temporal niche overlap was 0.912 for Chrysopidae and Coccinellidae in trees and 0.916 for Chrysopidae in ground cover and Chrysopidae in the trees. The largest niche similarity was 0.894 for Coccinellidae on trees and Chrysopidae on trees. The smallest temporal niche overlap was 0.500 for Aphidoidea and Pentatomidae and for Syrphidae and Pentatomidae. The smallest niche similarity was 0.182 between Aphidoidea and Pentatomidae (Table 1).
The natural enemy with the largest temporal niche overlap and niche similarity for Aphidoidea was Coccinellidae. The temporal niche overlap and niche similarity between Aphidoidea and Coccinellidae on trees was 0.818 and 0.769, respectively, and that between Aphidoidea and Coccinellidae in ground cover was 0.655 and 0.432, respectively. The temporal niche overlap and niche similarity between Aphidoidea and Chrysopidae was the lowest at 0.323 and 0.251, respectively. The natural enemy with the largest temporal niche overlap for Cicadellidae was Coccinellidae. The temporal niche overlap between Cicadellidae and Coccinellidae on trees was 0.824 and that between Cicadellidae and Coccinellidae in ground cover was 0.794. The natural enemy with the lowest temporal niche overlap for Cicadellidae was Syrphidae (0.542), and parasitic wasps (0.323) had the lowest niche similarity. The natural enemy with the largest temporal niche overlap and similarity to Pentatomidae was Chrysopidae. The temporal niche overlap was 0.788 for Chrysopidae on trees and 0.795 for Chrysopidae in ground cover, and the similarity was 0.551 for Chrysopidae on trees and 0.666 for Chrysopidae in ground cover. The natural enemy with the lowest temporal niche overlap for Pentatomidae was Araneida (0.477) and that with the lowest niche similarity was Syrphidae (0.199) (Table 1).
Temporal niche of pests and natural enemies in peaches with natural vegetative ground cover
In the natural ground cover areas, the pest with the largest temporal niche width was Cicadellidae (0.639) and the natural enemy with the largest temporal niche width was Coccinellidae on trees (0.660), followed by Coccinellidae in ground cover (0.611). The temporal niche overlap between Aphidoidea and Coccinellidae in ground cover was the largest (0.705). The niche similarity was the largest between Cicadellidae and Chrysopidae on trees (0.851). The temporal niche overlap and niche similarity between Aphidoidea and Pentatomidae was the lowest at 0.168 and 0.411, respectively (Table 2).
The natural enemy with the largest temporal niche overlap and niche similarity for Aphidoidea was Coccinellidae. The temporal niche overlap and niche similarity between Aphidoidea and Coccinellidae on trees was 0.691 and 0.812, respectively, and that between Aphidoidea and Coccinellidae in ground cover was 0.705 and 0.813, respectively. The temporal niche overlap and niche similarity was the lowest between Aphidoidea and Chrysopidae in ground cover (0.259 and 0.437, respectively). The natural enemy with the largest temporal niche overlap and niche similarity for Cicadellidae was Coccinellidae; the temporal niche overlap between Cicadellidae and Coccinellidae on trees was 0.638 and that between Cicadellidae and Coccinellidae in ground cover was 0.631. The natural enemy with the largest niche similarity for Cicadellidae was Chrysopidae on trees (0.851) and Coccinellidae on grass (0.836). The natural enemies with the lowest temporal niche overlap and niche similarity for Cicadellidae were parasitic wasps, at 0.226 and 0.431, respectively. The natural enemy with the largest temporal niche overlap and niche similarity for Pentatomidae was Chrysopidae. The temporal niche overlap was 0.767 for Chrysopidae on trees and 0.577 for Chrysopidae in ground cover. Niche similarity was 0.819 for Chrysopidae on trees and 0.678 for Chrysopidae in ground cover. The natural enemies with the lowest temporal niche overlap and niche similarity for Pentatomidae were parasitic wasps (0.219 and 0.459, respectively) (Table 2).
Temporal niche of pests and natural enemies in peaches with plowed ground
In the plowed treatment area, the pest with the largest temporal niche width was Cicadellidae (0.677) and the natural enemy with the largest temporal niche width was Coccinellidae (0.479). The temporal niche overlap between Aphidoidea and Coccinellidae was 0.911, and the niche similarity was 0.875; the temporal niche overlap value between Chrysopidae and Cicadellidae was 0.833, and the niche similarity was 0.780 (Table 3).
The temporal niche width of natural enemies was the largest in the treatment with the planted vegetative ground cover, and the activity time of Coccinellidae in the ground cover was longest. The niche width of Coccinellidae in the two vegetative ground cover areas was between 0.6 and 0.7. The niche width of Chrysopidae was larger (0.523) in the planted ground cover area than in the natural vegetative area (0.372). The niche width of Syrphidae was lower than that of other natural enemies (between 0.25 and 0.32). The ecological niche width of Araneida was higher in the artificial grass area (0.431) than in the natural grass area (0.299). The ecological niche of natural enemies on trees in plowed areas was the lowest, and the niche width and similarity between natural enemies and pests on trees were relatively different from those of other grass areas, which is not conducive to the reproduction of natural enemies.
Planted flowering plants in peach orchards can provide habitat and food resources for natural enemies, increase the population of natural enemies, reduce the population of pests, and significantly improve the pest control effects (Risch et al. 1983, Wan et al. 2011, Wang et al. 2015). Hairy vetch and marigolds planted among managed grasses provide nectar and other resources, which can continuously attract Coccinellidae, Chrysopidae, parasitic wasps, and Syrphidae, thereby significantly reducing the temporal niche of pests, increasing the temporal niche of natural enemies, and increasing the ecological niche overlap and niche similarity between pests and natural enemies. Vegetative ground covers, therefore, in orchards changed the correlation and temporal characteristics between natural enemies and pests, reduced the dependence of natural enemies on individual pest resources, and improved the stability of natural enemy populations.
This study was supported Shandong Provincial Colleges and Universities Youth Innovation Technology Program (2021KJ087), Shandong Provincial Natural Science Foundation (ZR2021QC188), and Shandong Agriculture and Engineering University Doctoral Foundation Project (sgybsjj2020-09).
Shandong Agricultural University, Tai’an 271018, China.