MARE REPRODUCTIVE LOSS SYDROME (MRLS)

Below you will find information I have sourced from the USA

In Australian the syndrome EAFL (Equine amnionitis and foetal loss) is the syndrome analogous to MRLS . There is a different caterpillar but related to the Kentucky processionary caterpillar. The preferred trees in Australia are the box eucalypts, white cedars and acacias – unfortunately very common in Queensland and in the Hunter. (this information courtesy of Dr Robyn Woodward from Equivet Australia)
If you have any photographs of the Australian caterpillars, nests,etc.. please send them in.

Controlled research experiments performed as collaborative efforts by Drs. McDowell, Williams, Donahue, Webb (University of Kentucky) and Newman (Venture Laboratories, Lexington, Kentucky) demonstrated that horses will inadvertently eat Eastern tent caterpillar's when the insects are present in the pasture or in other feedstuffs; MRLS -type abortions can be induced in experimental animals (mares or sows) by feeding them Eastern tent caterpillar; and the only part of the caterpillar that causes MRLS abortions is the exoskeleton (skin or cuticle). Eastern tent caterpillars are hirsute (hairy) caterpillars, and the experiments revealed that the hairs (setae) embed into the submucosa of the alimentary tract, creating microgranulomatous lesions (Figure 3). We hypothesized that those lesions allow bacteria from the mare’s alimentary tract, principally streptococci and actinobacilli, to invade the mare’s circulatory system. The bacteria then establish infections in tissues where the mare’s immune surveillance is reduced, such as the fetus and placenta. Fetal/ placental fluid bacterial infections lead to fetal death and abortion characteristic of MRLS (McDowell et al., 2004; Webb et al., 2004).

Controlling eastern tent caterpillars is vital to area horse farms, as the caterpillars have been strongly linked with outbreaks of Mare Reproductive Loss Syndrome (MRLS), which can cause late-term foal losses, early-term fetal losses and weak foals.

Horses will inadvertently eat the caterpillars and that the caterpillar hairs embed into the lining of the alimentary tract. Once that protective barrier is breached, normal alimentary tract bacteria may gain access to and reproduce in sites with reduced immunity, such as the fetus and placenta. Fetal death from these alimentary tract bacteria is the hallmark of MRLS. The time between a broodmares exposure to the caterpillars to abortion is approx. 10 days for an early pregnancy or sooner for a mare in later stages. Abortion is very quick and there are no obvious clinical warning signs.

Now is an optimal time for controlling populations because the caterpillars are still gathered together in the trees. Currently, small caterpillars are moving to feed on the leaves that have been appearing in trees and have built tents at branch and limb forks. Initial growth of the caterpillars will be slow, the caterpillars in limb nests will begin to move to the main truck branches and join together in a smaller number of large tents on individual trees. This aggregation behaviour can be used advantageously to manage the caterpillars by destroying or treating accessible populations.

After a few weeks, the caterpillars will leave the trees where they’ve eaten the available foliage and search for food to complete their development. Once the caterpillars have reached these dispersing stages, controlling them becomes much more difficult.

There are sprays that can be used to control or illuminate the caterpillars from your property. I have found a report that suggests the best spray to use is one called bifenthrin (Talstar) or carbaryl (Sevin). Both these chemicals have both stomach and contact activity so they can be effective when sprayed on foliage or tents (nests). The residual life of carbaryl is about a week; that of bifenthrin is at least two to three weeks. Regardless of the treatment used, it is important to revisit the sites in about five days to assess caterpillar activity. Additionally, experts recommend that horse farms scout for the telltale white tents in trees and err on the side of caution by keeping mares away from any caterpillar locations. Contact your local DPI and enquire as to what chemical or form of eradication they suggest. (good luck with that)

My suggestion would be to try to eradicate the moth and not wait for the actual caterpillars. If you know an area on your property has had the caterpillar infestation over the past few years - Keep an eye out for the moth and when you see the first one of the season, hook up a strong spotlight (even if you have to use a generator), set up some portable bug zappers near the spotlight for a few weeks and then judge the amount of nests and caterpillars you can find as opposed to the previous years.

Photo of a seta (hair) attached to an eastern tent caterpillar found below.

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The Eastern tent caterpillar (Malacosoma americanum)
In Australia they are referred to as Processionary Caterpillar (Ochrogaster lunifer)

The Eastern tent caterpillar is a univoltine, social species that forms communal nest in the branches of trees. It is sometimes confused with the gypsy moth, or the fall webworm and may be erroneously referred to as a bagworm which is the common name applied to unrelated caterpillars in the family Psychidae. The moths oviposit almost exclusively on trees in the plant family Rosaceae, particularly cherries (Prunus) and apple (Malus). The caterpillars are hairy with areas of blue, white, black and orange. The blue and white colours are structural colours created by the selective filtering of light by microtubules that arise on the cuticle.

The adult moth lays her eggs in a single batch in late spring or early summer. The egg masses contain on average 200-300 eggs. Embryogenesis proceeds rapidly and within three weeks fully formed caterpillars can be found within the eggs. But the small caterpillars lie quiescent until the following spring, chewing their way through the shells of their eggs just as the buds of the host tree begins to expand.

The newly hatched caterpillars initiate the construction of a silk tent soon after emerging. They typically aggregate at the tent site for the whole of their larval life, expanding the tent each day to accommodate their increasing size. Under field conditions, the caterpillars feed three times each day, just before dawn, at mid-afternoon, and in the evening after sunset. During each bout of feeding the caterpillars emerge from the tent, add silk to the structure, move to distant feeding sites en masse, feed, then return immediately to the tent where they rest until the next activity period. The exception to this pattern occurs in the last instar when the caterpillars feed only at night. The caterpillars lay down pheromone trails to guide their movements between the tent and feeding sites. The insect has six larval instars. When fully grown, the caterpillars disperse and construct cocoons in protected places. The adults (imago) emerge about two weeks later. They are rather strictly nocturnal, they start flying after nightfall, and possibly stop some hours before dawn already (Fullard & Napoleone 2001). Mating and oviposition typically occur on the same day as the moths emerge from their cocoons; the females die soon thereafter.

THE CATERPILLA ON THE MOVE

The Barbed Setae on the Caterpillars
The focus on the caterpillar led us to examine them under the Electron Microscope (EM, Fig 3c)). We noted, in passing, the barbed nature of the very fine setae that cover the exterior of the caterpillar and we noted that in some caterpillar species these setae are venomous and extremely effective offensive weapons. Although not recognized at the time, this was a critically important observation.