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Effects of pesticide use in fruit orchards on ground beetle diversity

INRA researchers examined the impact of pesticide use on ground beetle diversity (family Carabidae) in apple orchards in the Avignon region. Their work has revealed that reduced use of synthetic pesticides is associated with increased taxonomic and functional diversity in orchard ground beetle communities.

Pseudoophonus griseus (Coleoptera: Carabidae), France. © INRA, Pierre Zagatti
By INRA News Office, translated by Jessica Pearce
Published on 08/10/2015

Orchards harbor diverse soil fauna.  INRA scientists set up a circular study zone that spanned a 20-kilometer radius from the edge of Avignon and that included 15 commercial apple orchards. They looked at the effects of three types of orchard management practices—conventional fruit production, integrated fruit production (IFP), and organic fruit production—on the taxonomic and functional diversity of carabid beetles.

In particular, the researchers focused on beetle species that are especially abundant in agricultural settings and that are likely to be affected by pesticide use, even if they are not the intended target. Carabids are known to be good bioindicators in agricultural ecosystems and form associations with crop species. Beetles were collected across different seasons: in the spring, when orchard management was getting started; in the summer, when management was in full swing; and in the fall, two months after management ended. The goal was to study how beetle diversity was affected by pesticide use within and among management types. Over 1,073 individuals belonging to 46 different carabid species were collected and identified. Half of these species (26 out of 46) were considered to be rare because they each accounted for less than 0.5% of all the beetles collected.

Organic orchards have surprisingly low taxonomic diversity

The first major result of the study was that species number was influenced by season rather than by management type. In the spring, integrated and organic orchards had an average of more than two carabid species per sampling point. In contrast, in the autumn, conventional and organic orchards had less than one species per sampling point. Rather surprisingly, organic orchards were not the most taxonomically diverse. Although no synthetic pesticides are used in these systems, farmers nonetheless employ pest-control measures (organic or physical in nature), which can affect the various species these orchards harbor.

Organic orchards have greater functional diversity

The researchers then focused their attention on the functional diversity of the beetle communities, namely by characterizing the morphological features of the main carabid species collected. They examined beetle build, locomotor ability, and feeding-related traits. They assessed the mass, length, and width of around 100 individuals; they also took various measurements of the beetles’ limbs, wings, and mandibles.

The results of these analyses revealed clear seasonal patterns in most of the morphological data. However, two features were influenced by the type of management practice used:

  • the ratio between femur length and width was lowest in conventional orchards, which suggests that the beetles found therein are flyers rather than walkers
  • the ratio between mandible height and body length was greatest in organic orchards, which suggests they harbor more granivorous beetles

Finally, traits related to beetle locomotion, such as limb and wing features, were influenced by the interaction between management type and season.

The researchers also discovered that beetle feeding diversity, like beetle morphology, depended solely on management type. In contrast, habitat preference varied according to season, management type, and the interaction between these two factors.

Pesticide use and beetle ecological lifestyle

In summary, this research underscores the importance of looking beyond species number (which demonstrated no significant differences here) to focus on the morphological and ecological characteristics of the individuals being examined. This shift in approach can reveal key results in studies exploring how pesticide use affects animal diversity and behavior. It also highlights the need to carry studies out over longer time periods, so as to be able to better support one’s assertions and arguments.

These findings shed new light on the impact of pesticide use on biodiversity. In particular, they show that pesticide use is correlated with the reduced taxonomic and functional diversity of certain species and, more broadly, with decreased response variability. In conventional orchards, where pesticides are used extensively, migratory predatory beetles with well-developed wings are abundant. In contrast, in integrated and organic orchards, one can also observe short-limbed, ground-dwelling, granivorous beetles, which take advantage of the plant cover in such habitats.

This diverse fauna can only stand to benefit from reduced pesticide use in fruit orchards. However, the why and the how behind the patterns observed here remain to be explored.

Contact(s)
Scientific contact(s):

  • Mickaël Hedde Joint Research Unit for Functional Ecology and Ecotoxology in Agroecosystems (INRA, AgroParisTech)
Associated Division(s):
Environment and Agronomy
Associated Centre(s):
Versailles-Grignon

Going to the core of an apple orchard

On average, the apple orchards studied spanned 0.48 hectares. They experienced one of three management regimes:
• conventional fruit production, which uses fertilizers and synthetic pesticides
• integrated fruit production (IFP), which preferentially employs organic pesticides when possible; aims to generate high-quality fruit while limiting costs; and puts a greater emphasis on more environmentally friendly methods, which minimize undesirable secondary effects and reduce the use of agrochemicals
• organic fruit production, which uses microbial or organic insecticides and mineral fungicides rather than fertilizers and synthetic pesticides

Although consumers have very different opinions about these different management types, the regimes themselves do not have significantly different treatment frequency indices (TFIs). Instead, the main difference lies in the types of pesticides used. The TFI reflects the intensity of pesticide use by estimating the ratio of the applied dose to the recommended dose (for a standardized surface area). For instance, a hectare of land that receives 70% of the recommended dose would be assigned a value of 0.7.

reference

Hedde M., Mazzia C., Decaëns Thibaud, Nahmani Johanne, Pey Benjamin, Thénard Jodie, Capowiez Yvan. 2015. Orchard management influences both functional and taxonomic ground beetle (Coleoptera, arabidae) diversity in South-East France. Applied Soil Ecology 88: 26.