ARS | Publication request: External morphology of the egg of the native (Melitara prodenialis) and exotic (Cactoblastis cactorum) cactus moths (Lepidoptera: Pyralidae)

Submitted to: Proceedings of the Entomological Society of Washington
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 13, 2012
Publication Date: October 1, 2012
Citation: Baker, G.T., Hight, S.D., Brown, R.L. 2012. External morphology of the egg of the native (Melitara prodenialis) and exotic (Cactoblastis cactorum) cactus moths (Lepidoptera: Pyralidae. Proceedings of the Entomological Society of Washington. 114(4):433-438.

Interpretive Summary: Prickly pear cactus is native to the Americas. Many insects use prickly pear cactus for food and one such insect found in the southeastern U.S. is called the blue cactus moth. The moth stacks her eggs one on top of the other and creates a chain of eggs known as an eggstick. The eggs hatch at the same time, the caterpillars bore inside the prickly pear stems, and they develop feeding inside the cactus. A moth from Argentina, whose caterpillars also feed on prickly pear cactus, behaves similar to the blue cactus moth, and lays her eggs in an eggstick, became established in the southeastern U.S. The Argentine cactus moth is more destructive to prickly pears than the native blue cactus moth, and concerns have been raised about this non-native insect’s unavoidable and unwanted impact on native, agricultural, and ornamental cactus in its new homeland. Scientists with USDA Agricultural Research Service, Center for Medical, Agricultural, and Veterinary Entomology, Gainesville, Fl and Mississippi State have studied the eggs of these two species to look for differences that would be useful to identify the eggs of the two cactus moths. By using an electron microscope, slight differences between the two species were identified. These differences are visible on the surface of the egg, only under very high magnification, and involve the shape of cells at specific locations. These cells in the blue cactus moth have a looping pattern and in the Argentine cactus moth they are polygonal in shape.

Technical Abstract: Scanning electron microscopy was used to study the morphology of the chorionic surface of two pyralids that feed on Opuntia cactus. The chorionic surface of Cactoblastis cactorum has a reticulate pattern due to the ridges on the surface and aeropyles. The surface has a granular appearance at low magnifications and rugose at high ones. The micropylar area has a central depression with the micropyles and is surrounded by irregularly shaped polygonal cells. The tertiary cells have aeropyles associated with the cells, and these aeropyles have mesh-like extensions that cover their openings. The general appearance of the chorionic surface of Melitara prodenialis is similar to C. cactorum, but the micropylar region differs in that cells surrounding the micropylar depression are looping cells of varying sizes. Also, no aeropyles are associated with the looping cells around the micropylar region.