By Bethany Schneekloth
It was the middle of summer and the milkweed plants outside of the house were covered with monarch caterpillars, but upon closer inspection with my dad and younger siblings, we began to notice that there weren’t many chrysalises around the area and the ones that we did see were odd. We decided to start bringing them inside like we do most years. We brought in at least 80 caterpillars, with only 20 of them making it to become butterflies. While we were saddened by this outcome, we took time to start looking into why so many of them were dying and how we could change our plan for next summer, and we found four main causes: OE, the tachinid fly, the chalcid wasp, and NPV.
Ophryocystis elektroscirrha, or OE, is a type of parasite that infects insects that thrive on the milkweed plants, such as monarch butterflies. Discovered in the late 1960s in Florida, this parasite has spread to the rest of the continental USA, Hawaii, Australia, Cuba, and Central and South America, slowly helping to decrease the monarch butterfly population. The parasite’s life cycle begins as small spores that are transferred from the abdomen of the female butterfly as the eggs are laid, they are then eaten by the caterpillars which introduces them to their host, the parasite goes through two stages of vegetative reproduction before the caterpillar pupates where the parasite will begin to multiply, and once the butterfly emerges from its chrysalis the spores are connected to the abdomen and the cycle begins again. You can tell if a caterpillar is infected by looking for highly noticeable grey spots lining its sides.
The tachinid fly is a parasitic fly that lays its eggs on unhatched monarch eggs or on the sides of growing caterpillars. This parasite is almost impossible to detect unless that caterpillar is dead, either within the chrysalis or out. There is no chance of a butterfly surviving whilst infected with a tachinid fly because when the maggots are fully grown they forcefully leave the body after depriving the growing caterpillar of its nutrients; butterflies infected with the tachinid fly climb as high as they can to form their chrysalis but many die as they begin to form up and they die suspended in a J-shaped manner with one or more white strings cascading out of their sides. This string is used by the maggots to safely exit its host and get to the ground. A caterpillar can host up to six maggots and when you collect the dead body, if you have it inside, make sure you squish all of the maggots or the maggots pupae which are brown and usually in a darker area. The most you can do to stop the spread of this parasite is to make sure you squish all maggots if you have the caterpillars inside; there is nothing else you can really do, just like the next killer which is a disease that comes hand in hand with the next parasite and bacteria.
The chalcid wasp is a group of over 22,000 species, of which only one has been linked to parasitising monarchs and other butterflies – the pteromalus puparum. Their parasitic life cycle begins as the eggs are laid inside of the caterpillar, and slowly kills the insect. When infested with chalcid wasps the chrysalis will turn soft and become discolored and there will be holes where the wasps emerged, but if the caterpillar doesn’t make it to pupating it will turn black. A caterpillar turning black can also be a sign of the nuclear polyhedrosis virus, or NPV. NPV is transferred from the overly wet soil to the plant and then to the caterpillar, it causes the caterpillar to be slower and show signs of not being hungry. Towards the end of the caterpillar’s life it will climb to the topmost point and basically liquidize whilst turning black. Since it was introduced to our caterpillars through the plants we decided to cull our section of milkweed plants and get some non-infected plants for next year’s season.
Bethany Schneekloth is a student at Mabel-Canton High School. She is one of eight area students participating in the Journal Writing Project, now in its 21st year.