Palo Verde Bean Weevil
Mimosestes amicus
Photo taken June 10, 2012 near Bumblebee, Yavapai Co., Arizona. June 2010. Sitting on bean pod of foothill palo verde.
Large seeds give a new plant seedling a boost towards survival. But they also represent a resource to be exploited by seed predators. Bean weevils lay their eggs on the surfaces of the bean and then as the larva hatches out it bores straight down into the bean - the entrance hole is minute or invisible. Once the inside of the bean is largely hollowed out, the larva pupates inside and later ecloses and tunnels out as an adult beetle. The exit hole is very smooth and drilled through the hard seed coat. A seed thus consumed will not germinate, i.e. the whole plant was predated by the beetle. There are many bean weevil species found in the Sonoran Desert with preferences for various bean-seeds.