Allantoin Crystal Formation in Bagrada hilaris (Burmeister) (Heteroptera: Pentatomidae) Females

Bagrada hilaris is a polyphagous herbivore reported as an invasive pest in the United States. During the course of dissecting Burmeister hilaris unique crystals were observed in both the midgut and oviducts. Crystals were identified using X-ray diffraction techniques. Both acicular (i.e., needle-like, slender, and/or tapered) and cubic (i.e., cube shaped) crystals were observed in six of 75 individuals examined (8.0%). The crystals were mainly observed in females (6.7%), followed by males (1.3%) with no crystals observed in the minimal number of nymphs examined (0%). Crystals of both types were detected in the midgut and lateral oviducts of the females and midgut in males. The acicular crystals often appeared as distinct bundles when present in the midgut and oviducts. Crystals varied in size with the acicular crystals ranging from 0.12 mm to 0.5 mm in length although the cubic crystals ranged in length from 0.25 mm to over 1.0 mm with widths of ∼0.25 mm. The cubic crystals were identified as allantoin although the acicular crystals were most likely dl-allantoin in combination with halite. While allantoin in a soluble form is often found in insect tissues and excreta; being present as a crystal, especially in such a large form, is curious and raises some interesting questions. More research is warranted to further understand mechanisms associated with such crystal formation in B. hilaris and can lead to a better understanding of the excretory process in this species and the role allantoin plays in the elimination of excess nitrogen.