Hemileuca lucina

Oviposition refers to a process in which animals lay eggs. Hemileuca lucina females lay eggs in batches three months after the larval developmental period, which is usually around September. Females tend to make one or very few decisions on where to deposit the eggs. This is different from other species that oviposit eggs singularly as it is known that they make hundreds of decisions on where to oviposit the eggs, when to oviposit the eggs, etc. The flight time of Hemileuca lucina is about two weeks during September and they lay eggs once a year (univoltine). Hemileuca lucina females expand their wings, which is often seen as a signal for hormone production. The hormone is used to attract males and once males are with females, they copulate for about one to two hours. The host plant in which females oviposit eggs is called Spiraea latifolia and they usually lay one or two batches of eggs on the stem of the host plant.[1]

Females use their abdomen and shift it left and right around the twig and start laying eggs in a half-circle. At first, these half-circles of eggs are nearly empty, lacking any form. Females then re-crawl up the twig to fill in the gaps, which makes the batch of eggs look like a long ring. These eggs overwinter and hatch around May. Local weather conditions are one of the known factors that can change the hatching period.[1] It was also observed that females preferred the periphery of the twig for their oviposition location as sunlight was more abundant compared to the inner side. Shady regions were avoided for most of the females but the reason is not fully understood.[1]

Larval response to predators or other harmful factors are mainly defense or escape. Defense takes on multiple forms, as larvae thrash, bite and regurgitate when near predators. Such defensive behavior is mostly seen in larvae of the first three instars. Aggregation behavior can be explained by the early instar larvae's tendency to group together to defend themselves against predators. Once larvae enter the fourth instar however, they show escape behaviors as most larvae are in solitary phase. Escape behavior also takes on multiple forms as larvae drops from the host plant to the ground or cringe and curl tightly on the plant. As a result of escaping, late instar larvae tended to disperse rather than aggregate.[10]

An average of 146 eggs are laid per batch. Each egg weighs around 1.63 mg and ranges from 1.13 to 1.89 mg. The specific time in which the eggs are laid does not seem to determine larval fitness. Similarly, the range of egg weight seems insignificant as there is no known information on whether or not quality/health of larvae depends on egg weight. However, female age seems to control egg weight, as the weights declined as females aged. The eggs hatch in May.[1]

Larvae

Generation for Hemileuca lucina larvae starts around May and lasts until July.[11] Larvae are black and have spines on their back that are black and orange. These spines can cause pain through dermatitis when handled improperly. During the first four instars, larvae show gregarious behaviors as they move in clumps. Group size tends to decrease over time due to various factors including weather, predators, parasitoids, food availability, etc. During the fourth and fifth instars, most larvae show solitary behavior. During the sixth instar, larvae are completely solitary and display yellow stripes on their back.[1]

During this stage, larvae move away from the host plant and burrow into the ground for pupation. The pupa resides in the soil for the entire summer until September.[1]

Adult New England buck moths usually emerge in the morning, faster than its sister species, Hemileuca maia.[3] Flight season is about two weeks long for adult moths. Flight usually occurs in September but, depending on weather conditions, it often occurs in October. Males are known to fly in the late morning and mating occurs around 10:00 am – 1:00 pm. After copulating for about two hours, females find host plants for oviposition.[1]

Few predators of Hemileuca lucina larvae have been reported, including wasps, stinkbugs and orb-weaving spiders. Specifically, vespid wasps (Polistes dominula and Polistes fuscatus) have shown to prey upon H. lucina caterpillars that are masticated and given to wasp larvae as nutritional sources. It was observed that wasps attack one member of the group rather than attacking multiple larvae at the same time but the specific method of wasp predation requires further investigation. Moreover, H. lucina larvae's spines are known to be ineffective against some social wasps (P. dominulus and P. fuscatus) as they are able to bite off the spines before masticating the larvae.[2] Stinkbugs such as Podisus maculiventris are also reported predators of gregarious caterpillars like H. lucina, but their interaction with the caterpillars are rarely observed due to low numbers of stinkbugs in the spring.[12] It has been observed that adult moths are attracted to three species of araneid spiders and their webs. The specific cause behind the moth's attraction to these webs is not known but pheromone mimicry seems to be the widely used strategy in these spiders.[3]

There are few notable parasites of Hemileuca lucina caterpillars including tachinid fly (Compsilura concinnata) and ichneumonid wasp (Ichneumonidae - Hyposoter fugitivus), both of which are not H. lucina specific parasites. Of these two, C. concinnata is responsible for mortality of H. lucina caterpillars as 30% mortality was found in Massachusetts.[5] Even though C. concinnata is a major cause of H. lucina caterpillar mortality, its predation is not specific to H. lucina caterpillars as 36% mortality on Hemileuca maia was found in southern Massachusetts.[4] It was observed that C. concinnata attacks each H. lucina caterpillar aggregation and ultimately lays live larvae in the host. The specific mechanism in which the tachinid fly lays the larvae needs further investigation. It was also found that the tachinid fly's attack triggers H. lucina caterpillars to separate from the aggregation by dropping off the host plant or inducing solitary status. In both cases, the tachinid fly then had an advantage to prey on the separated larvae that fails to rejoin the aggregation.[5] Similarly, ichneumonid wasps do not only parasitize on H. lucina as there are reported incidents of H. maia getting parasitized.[5]