Contribution of predation to the biological control of a key herbivorous pest in citrus agroecosystems

Abstract

Biological control has traditionally simplified the view of trophic relationships between herbivorous pests and their natural enemies in agriculture. The success or failure of this pest management strategy is still mainly attributed to the ability of a few key natural enemies to suppress the pest density. For example, successful regulation of the California red scale (Aonidiella aurantii), a key citrus pest, is generally credited to specific parasitoids of the Aphytis genus. Currently, research is revealing how herbivore regulation in agroecosystems can be alternatively achieved with a greater number of trophic associations within the system. The goals of the present study were as follows: i) to unravel species‐specific trophic links between A. aurantii and its natural enemies in citrus agroecosystems, and ii) to assess their contribution to control of A. aurantii. Predation and parasitism of this herbivorous pest were assessed through exclusion experiments. Species‐specific trophic links between this herbivorous pest and its natural enemies were studied using gut‐content analysis of field‐collected predators employing prey‐specific DNA molecular markers. Relative predation rates of the species involved in A. aurantii regulation were estimated. Predation was found to be the main biotic component of A. aurantii mortality, causing reductions of more than 75% in recently settled cohorts. Aonidiella aurantii DNA was detected in the digestive system of 11 species of predators. Generalist and stenophagous predators, mainly associated with other citrus pests such as aphids, proved to be the most important biological control agents of this pest. Complex trophic relationships, such as apparent competition between two key citrus pests, were revealed. The present study highlights the role of predation as biotic mortality factor of key pests in perennial agroecosystems, wherein it is a rich complex of indigenous or naturalized generalist predators that are primarily responsible for this mortality. The results herein presented may therefore offer another perspective on the biological control of one of the key world‐wide citrus pests, at least in those regions where specific parasitoids are not able to successfully regulate the scale populations.

Economic value of conservation biological control for management of the Asian citrus psyllid, vector of citrus Huanglongbing disease

“…It focuses on the impacts related to the loss of effective ecological services derived from natural enemies that help sustain the productivity of citrus agroecosystems, without the need for costly input. HLB is considered the most damaging citrus pathosystem across the world, but the prevalent intensive insecticide control strategy disregards CBC services, which are pivotal for herbivore vector regulation . Our evaluations provide evidence that the loss of natural ACP pest regulation services would significantly impact the economic viability of the citrus industry in regions where HLB is present.…”

“…The economic costs of the loss of pest regulation services by CBC for the suppression of ACP is just a small fraction of the total ecological impact associated with an effective CBC strategy and its potential economic value. Citrus agroecosystems harbor a highly abundant and diverse complex of natural enemies able to effectively regulate populations of multiple herbivorous species, including key crop pests, through complex trophic interactions . Intensive insecticide management of ACP strongly affects natural enemies and threatens to disrupt these inter‐trophic interactions.…”

“…The holistic nature of IPM demands an extensive knowledge of the agroecosystem in order for it to be successfully implemented. Insufficient knowledge of the ecological processes which modulate the pest demography and the shortages of economic evaluations to the benefits of IPM implementation are the main causes of its shortcomings …”

“…Cultural and pest management practices that aim to increase natural enemy abundance and functional diversity are known collectively as conservation biological control (CBC). The effective implementation of CBC requires detailed knowledge of the agroecosystem . Economic benefits resulting from CBC are even harder to estimate than those for other BC approaches and are therefore commonly ignored …”

“…Citrus agroecosystems have been recognized to harbor rich complexes of natural enemies that can effectively reduce the economic injury of most phytophagous arthropods associated with the crop . Comprehensive studies on this system have facilitated the development of complex and successful IPM programs that are considered paradigmatic in modern agriculture …”