Cacao flower visitation: Low pollen deposition, low fruit set and dominance of herbivores

Abstract

Pollination services of cacao are crucial for global chocolate production, yet remain critically understudied, particularly in regions of origin of the species. Notably, uncertainties remain concerning the identity of cacao pollinators, the influence of landscape (forest distance) and management (shade cover) on flower visitation and the role of pollen deposition in limiting fruit set. Here, we aimed to improve understanding of cacao pollination by studying limiting factors of fruit set in Peru, part of the centre of origin of cacao. Flower visitors were sampled with sticky insect glue in 20 cacao agroforests in two biogeographically distinct regions of Peru, across gradients of shade cover and forest distance. Further, we assessed pollen quantities and compared fruit set between naturally and manually pollinated flowers. The most abundant flower visitors were aphids, ants and thrips in the north and thrips, midges and parasitoid wasps in the south of Peru. We present some evidence of increasing visitation rates from medium to high shade (40%–95% canopy closure) in the dry north, and opposite patterns in the semi‐humid south, during the wet season. Natural pollination resulted in remarkably low fruit set rates (2%), and very low pollen deposition. After hand pollination, fruit set more than tripled (7%), but was still low. The diversity and high relative abundances of herbivore flower visitors limit our ability to draw conclusions on the functional role of different flower visitors. The remarkably low fruit set of naturally and even hand pollinated flowers indicates that other unaddressed factors limit cacao fruit production. Such factors could be, amongst others, a lack of effective pollinators, genetic incompatibility or resource limitation. Revealing efficient pollinator species and other causes of low fruit set rates is therefore key to establish location‐specific management strategies and develop high yielding native cacao agroforestry systems in regions of origin of cacao.

Birds and bats enhance cacao yield despite suppressing arthropod mesopredation

“…Plant‐arthropod interactions limiting cacao productivity at different stages of its life cycle are complex, geographically variable and remain largely unclear (Toledo‐Hernández et al, 2017; Vansynghel, Ocampo Ariza, et al, 2022). The combination of multiple methodologies allowed us to connect the presence of top predators and ants with multiple functions within agroecosystems, but a detailed understanding of trophic interactions within agroecosystems likely requires additional approaches.…”

“…Sustained productivity of neotropical cacao agroforestry systems is hindered by multiple constraints during the cacao life‐cycle, including low pollination success, leaf and flower herbivory, and other pests and diseases reducing crop yields (Vansynghel, Ocampo Ariza, et al, 2022). Among arthropod pests, caterpillars of the pod and bark borers Carmenta foraseminis and C. theobromae (Lepidoptera: Sesiidae), and the mirid Monalonion dissimulatum , are considered to cause the most important yield losses (e.g., Carabalí Muñoz et al, 2018; Vargas et al, 2005).…”

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

“…Flower counts started two weeks earlier than the fruit counts and both counts were repeated every 14 days over a period of 1 year. As in other studies [ 25 ], small fruits between 1 cm and 3 cm were summed per tree, over the year. Fruits less than 7 days old are smaller than 1 cm and thus not large enough to be reliably monitored.…”

“…For example, typically, more birds and bats can be found foraging in cacao agroforests closer to the forest than at further distances [ 22 ]. As for arthropods, there is evidence of certain cacao flower visitors [ 25 ] and ant species [ 26 ] being impacted by increasing distance to forest, though this is not consistent across studies [ 23 ]. Forest distance and shade cover thus have important implications for biodiversity and the ecosystem functions they provide.…”

Factores asociados a la polinización del cultivo de cacao (Theobroma cacao L.)

“…Con respecto a los géneros de polinizadores de cacao, el Forcipomyia (Diptera: Ceratopogonidae) ha sido reportado en países de centro y Suramérica, tiene un pequeño tamaño que le permite polinizar la flor, frente a otros polinizadores como abejas o mariposas (Alvarado Aguayo et al, 2018;Jiménez Martínez & Antúnez Munguía, 2021;O'Doherty & Zoll, 2012;Vansynghel et al, 2022;Young, 1983). En Indonesia este género ha sido reportado en mayor abundancia en épocas lluviosas (Zakariyya et al, 2016).…”