Agonopterix alstroemeriana

A. alstroemeriana is a wide-ranging species native to Europe, that has more recently spread to North America, Australian and New Zealand.[2][3] In North America, it is most common to the northeastern and northwestern United States, as well as the southern regions of Canada. It has spread inland in both nations, and can now commonly be found in the Midwestern states of the U.S. as well.[3]

The first North American sighting of the hemlock moth was of a caterpillar seen in Tompkins County, New York in 1973.[1] After that, Agonopterix alstroemeriana spread quickly throughout the United States. It was found in the Pacific Northwest in 1983–1985, possibly spread by the accidental shipping of dormant moths.[3] The moth was seen in the Midwest starting in 1990, when it was discovered near Columbus, Ohio.[1] It was established in Illinois in 1993, after being identified by the rolled leaves of Conium maculatum, a characteristic indication of the presence of A. alstroemeriana.[6]

The species has been breeding in New Zealand since 1986 and it is likely that the moth then spread from New Zealand to southern Tasmania, where its presence was discovered in 2019.[7]

The poison hemlock moth can be found wherever its host plant (Conium maculatum) occurs. Thus, the moth is most commonly seen in open fields and roadsides in suburban and rural locations.[3] In the U.S., A. alstroemeriana often winters under the bark of firewood; then flies away after being warmed up when the wood is brought into the house. Moths also may come inside buildings and housing during the night, as they are attracted to light.[2]

The caterpillars in earlier instars form tubes from the leaves of Conium maculatum by rolling the leaves together using a secreted webbing material. Older caterpillars make tubes from the flowers and seed heads as well as the leaves. Abandoned tubes can regularly be found on the poison hemlock plant because, if disturbed or attacked, the caterpillar will wriggle free of the tube and onto the ground as a predation defense mechanism.[2]

Around 200 small eggs are laid by the female, and they are placed on the underside of the leaves of their host plant, Conium maculatum. As eggs, they have a pale color.[2]

Agonopterix alstroemeriana larva in a later instar

The eggs hatch into caterpillars about 6 days after being laid. Earlier instars are yellow with a black head capsule.[5] After feeding on their hostplant and growing in size, the caterpillars have a light green color. After almost a month of growth, the caterpillars are around 10 mm long (.4 in).[2] The last instar larva is green with three dark green stripes.[5] Larvae often emerge in April and May.[3] Hemlock moth larvae have been known to shelter together in high numbers, since the larvae seem to repel predators with toxic alkaloids obtained from its host plant. They also have the advantage of local predators being less familiar with the species because they are non-native.[3][4]

The caterpillar may also benefit from the toxic alkaloids present in the poison hemlock host plant because they may increase the ability of A. alstroemeriana to recognize Conium maculatum as the correct location for oviposition.[4]

They pupate for 2 weeks in the soil, usually from late May to early June.[2][5] The color of pupa is red-brown, with fine hairs densely located. The length of pupae is approximately 6–7 mm.[5]

An image of an adult A. alstromeriana showcasing its coloration

After pupating, the moths emerge from the soil as adults. This adult emergence usually occurs in mid- to late- June.[5] The adults must therefore stay alive through the winter in order to breed during the spring. Adults generally live from June to March, making A. alstroemeriana a relatively long-lived moth species.[2]

The use of A. alstroemeriana as a biological control method has been limited by the scarcity of information on its life history and feeding habits and the ability to harvest the larvae only in early to mid-spring.

Due to C. maculatum’s ability to serve as a stock for a variety of plant diseases, and to overrun fields growing cattle feed, it has been implicated in killing multiple species of plants. Poison hemlock commonly overruns fields growing feed for livestock, which creates the possibility of killing the animals (through hay contamination). Therefore, agriculturalists have made it a priority to address the widespread nature of poison hemlock.[4]

Leaves of Conium maculatum, the hostplant of A. alstroemeriana

The number of eggs that A. alstroemeriana lays is known to be associated with the dry weight of the leaf. However, oviposition was not correlated positively with the concentration of alkaloids in the poison hemlock, which varies widely among individual plants.[9] Therefore, it is difficult to predict whether increased alkaloids in the plant would increase or decrease the use of the hemlock moth as a biological control.

The effects that the alkaloids in Conium maculatum cause on the moth, both physiologically and behaviorally, are relatively unknown. Persons interested in the biological control capabilities of A. alstroemeriana see behavioral dependency on the host plant as an asset when using this moth as a biological control agent, because this reduces the possibility of the moth affecting other species besides the host plant.

Preliminary research has not found any negative physiological effects caused by the high alkaloid toxicity of poison hemlock. The moth may actually benefit from the alkaloids present in its feeding behavior.[4]