Monarch butterflies are facing extinction. The cause might just be a Tachinid, a beneficial fly (beneficial to agriculture) but not to Monarch butterflies. See video clips 1 & 2.
"In some species, eggs are deposited on foliage near the host insect, and the maggots are ingested during feeding by the host after they hatch. In other species, the adult fly glues eggs to the body of the host, and the maggots penetrate into the host's body after the eggs hatch. Some female tachinids possess a piercing ovipositor and insert their eggs into the host body. In all cases, tachinid maggots feed internally in their hosts and exit the host body to pupate." --From University of California Agriculture and Natural Resources.
The following four photos are to aid in the identification of the tachinid fly parasite in our South Laguna Beach study.
"A study looking at the rates of parasitization by the most common tachinid parasitoid of Monarchs, Lespesia archippivora, showed that about 13% of wild Monarch caterpillars contained these parasitoids!" --Matthew L. Gimmel, Ph.D. Santa Barbara Museum of Natural History
So how do Tachinid eggs get onto and into a Monarch caterpillar?
James E. O'Hara http://www.nadsdiptera.org/Tach/AboutTachs/TachOverview.html
"The ancestral mode of host finding in Tachinidae likely involved a series of cues, olfactory and visual, that guided a searching female to the right microhabitat and host plant and then to an exposed host, where perhaps tactile stimuli initiated oviposition behavior. This method of host location is still common, but there are many sophisticated behaviors that have evolved to aid the searching tachinid. For example, oviposition in numerous tachinids does not involve the visual sighting of a host. In the case of Goniini, microtype eggs are deposited on the food plant of a host, usually in response to plant volatiles released at the site of feeding damage, and the eggs do not hatch until ingested by a host."
"Tachinid flies and other parasitoids exert selection pressures on their hosts to evolve ways in which to minimize parasitism. The more obvious may involve the evolution of cryptic coloration, specialized feeding strategies such as concealed feeding or feeding at night, or evasive maneuvers that are evoked when a host is attacked. Less obvious, but quite important at the community level, are the effects of tachinid parasitism on host and host-plant interactions (i.e., tritrophic interactions). Insect herbivores do not always feed preferentially on plant species that provide the highest nutrition. Certain insect herbivores will feed on less preferred host plants if such feeding reduces their level of mortality due to parasitism. The investigation of enemy-free space as an important component of tritrophic interactions is an active area of research."
Click HERE for the entire O'Hara article.
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