Agrochemical bioaccumulation in pitaya cacti (Stenocereus queretaroensis) and its effect on bat interaction and yield

Bats are among the most valuable pollinators of economically important crops in Mexico including agaves and columnar cacti. High demand for the agricultural products of these crops has resulted in increasing use of agrochemicals, including pesticides and fertilizers, to increase yield and decrease pest damage. However, these compounds can negatively affect crop mutualists such as pollinating bats. In this study, we investigated: (i) how the application of the broad-spectrum pesticide carbamate and/or synthetic fertilizers affect crop yield of the pitaya cacti (Stenocereus queretaroensis); (ii) whether carbamate bioaccumulates in pitaya nectar and fruits; and (iii) whether the application of these agrochemicals affects visitation rates of the pitaya's most efficient pollinators, nectarivorous bats of the genus Leptonycteris. We designed an experiment consisting of four treatments (pesticide, nutrients, both, or neither) applied to pitaya plants. We estimated the effect of each treatment by quantifying pitaya reproductive structures (flower buds and flowers) and fruit yield and quality, performed trace analysis to detect the pesticide in the nectar and fruits, and estimated bat flower visitation rates using camera traps to determine whether the addition of agrochemicals influenced pitaya-bat interactions. We found that none of the treatments increased yield or fruit sweetness, and they did not affect bat visitation rates. Fruit pulp and floral nectar contained pesticide concentrations above those permitted by international environmental agencies. Thus, our results show that adding these agrochemicals to pitaya crops does not improve yield but could negatively affect their crop pollinators, especially since bats apparently do not avoid visiting flowers containing pesticide residues.