Bedtime Story to My Mother: Virgin Females Seek Love

TL;DR

This study explores how virgin female bagworms seek mates in different species and environments, focusing on their mating success and timing.

Contribution

The study introduces neotenic female bagworms as a model system to better understand reproductive processes in insects with complete metamorphosis.

Findings

Calling females are long-lived relative to males and mate when male abundance is high.

Low mating success occurs during early season male shortages or late adult emergence in northern populations.

Synchronous larval development leads to a decline in live calling females over time in all three species.

Abstract

In organisms with obligatory sexual reproduction, females are born virgin and need to access male sperm over the course of their life to produce offspring. This problem is simplified in holometabolous insects with complete metamorphosis because food acquisition and sexual activities are segregated into separate life history phases (transition between larval, pupal, and adult stages). Unfortunately, female transition from virgin to mated status in feral populations is challenging to quantify due to the high mobility, small size, and cryptic nature of adult insects. Neotenic female bagworms reproduce within a self-constructed bag, thus providing a model system to parameterize reproductive processes.

The probability that female bagworms (Lepidoptera: Psychidae) are in mating time-in (live pheromone calling) was recorded in three bagworm species: Oiketicus kirbyi in a Costa Rican oil palm plantation in 1993–1994; Metisa plana in Malaysian oil palm plantations during five consecutive generations of bagworms in 1996; and Thyridopteryx ephemeraeformis on ornamental trees in the Midwest United States. Because females entirely reproduce within their bag (mate attraction, copulation, and oviposition), it is possible to assess the mating success of time-out females (dead individuals from an ongoing generation that either mated or died as a lifelong virgin) and incidence of calling females that may or may not mate before death. Synchronous larval development and discrete (non-overlapping) generations imply a declining proportion of live calling females over time in all three bagworm species: ‘young’ calling females prevail in the early season as opposed to a majority of time-out (post-reproductive) females in the late season. Calling females are long-lived relative to males (one-day lifespan) and thus expected to mate as adults when abundance of males is high and/or female longevity exceeds three days. A low mating success of calling females is associated with extreme protogyny (early season male shortage; O. kirbyi in 1994) or late adult emergence in populations at the edge of the distribution range (T. ephemeraeformis at latitudes > 41° N in 2019).

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