Quantifying services and disservices provided by insects and vertebrates in cacao agroforestry landscapes

Abstract

Animals provide services such as pollination and pest control in cacao agroforestry systems, but also disservices. Yet, their combined contributions to crop yield and fruit loss are mostly unclear. In a full-factorial field experiment in northwestern Peru, we excluded flying insects, ants, birds and bats from cacao trees and assessed several productivity indicators. We quantified the contribution of each group to fruit set, fruit loss and marketable yield and evaluated how forest distance and canopy closure affected productivity. Fruit set dropped (from 1.7% to 0.3%) when flying insects were excluded and tripled at intermediate (40%) compared to high (greater than 80%) canopy cover in the non-exclusion treatment. Fruit set also dropped with bird and bat exclusion, potentially due to increased abundances of arthropods preying on pollinators or flower herbivores. Overall, cacao yields more than doubled when birds and bats had access to trees. Ants were generally associated with fruit loss, but also with yield increases in agroforests close to forest. We also evidenced disservices generated by squirrels, leading to significant fruit losses. Our findings show that several functional groups contribute to high cacao yield, while trade-offs between services and disservices need to be integrated in local and landscape-scale sustainable cacao agroforestry management.

Birds and bats enhance cacao yield despite suppressing arthropod mesopredation

“…Fresh cacao beans in our study area are typically delivered by farmers to the cooperative's facilities directly after harvesting. All pods infested by fungal diseases (only six cacao pods), or attacked by squirrels (52 cacao pods) were discarded by farmers upon observation, and were not incorporated in our assessments of yield, which included a total of 596 cacao pods (Vansynghel, Ocampo‐Ariza, et al, 2022). In contrast, damage by mirids frequently does not reach the endocarp of cacao pods, and fruits are harvested as normal.…”

A scarab beetle (Coleoptera: Scarabaeidae) causes tree mortality, delayed growth, and yield reduction in cacao with genotype‐specific susceptibility to herbivory

“…In addition, potential biological control agents, such as insectivorous birds and bats, and ants, have emerged as candidates for suppressing herbivorous insects and enhancing cacao crop yields. 67,68 Furthermore, the use of the entomopathogenic fungus Metarhizium anisopliae and entomopathogenic nematodes has proven effective in targeting beetle larvae from the Rutelinae subfamily. 69 Understory plants may serve as alternative hosts for L. femoratus larvae, particularly during the establishment phase, making their correct management crucial for controlling its populations.…”

“…One of the foundational elements for such a program, as demonstrated in this study, should be the identification and production of resistant cacao cultivars. In addition, potential biological control agents, such as insectivorous birds and bats, and ants, have emerged as candidates for suppressing herbivorous insects and enhancing cacao crop yields 67,68 . Furthermore, the use of the entomopathogenic fungus Metarhizium anisopliae and entomopathogenic nematodes has proven effective in targeting beetle larvae from the Rutelinae subfamily 69 .…”

Pest suppression by bats and management strategies to favour it: a global review

“…For example, the trade‐offs between services and disservices also need to be properly assessed to understand the true magnitude of the ecosystem services bats provide and to establish clear guidelines to enhance these (see, e.g. Vansynghel et al ., 2022), but this layer of complexity has often been disregarded to date.…”