Day-night temperature differential, rather than mean temperature, determines age of sexual maturation in Straicosta albicosta (Noctuidae)

Highlights

• We investigated calling behaviour of univoltine noctuid moth (western bean cutworm).

• Calling behaviour varied as a function of female calling age.

• Mean temperature and humidity did not directly affect calling behaviour.

• Pre-calling period was shorter with larger day-night temperature difference.

• Selection pressure for plasticity in calling behavior might depend on voltinism.

Abstract

While pheromone traps have been effectively used to monitor the recent range expansion of the western bean cutworm (WBC), very little is known about the pheromone mediated reproductive biology of this species. The age at which females initiated calling (the behaviour associated with the release of the sex pheromone), and the pattern of calling on the first three nights following sexual maturation were determined for virgin females held under four temperature regimes (25:20; 25:15; 20:15; 20:10 °C L:D and 16L:8D photoperiod), and two RH (60 and 80%). Regardless of the rearing conditions the pre-calling period (PCP) was always several days post emergence, supporting the hypothesis that WCB is a migrant species. However, surprisingly the length of the PCP was not directly related to mean temperature but rather to the temperature differential between the photophase and the scotophase. The duration of calling increased with female age, but unlike in other moths was not affected by the abiotic factors tested. The relative insensitivity to temperature and humidity, when compared with many other moth species, may be related to the WBC being a univoltine species with a mid-summer flight period. Consequently, there would not be strong selection pressure for plasticity in calling behavior when compared with the case of multivoltine species that experience a wide range of environmental conditions during different seasonal flight periods.

Introduction

Many moth species (Lepidoptera) rely on pheromone mediated communication for mating, and many studies have underlined the effects of biotic (e.g. age, autodetection, suitable host plants: Delisle, 1992, Holdcraft et al., 2016, Jacas and Peña, 2002, Landolt and Phillips, 1997, Noldus and Potting, 1990, Reddy and Guerrero, 2004, Rehermann et al., 2016, Turgeon and McNeil, 1982) and abiotic (e.g. temperature, photoperiod, relative humidity, wind speed and changes in atmospheric pressure: Delisle and McNeil, 1987a, Delisle and Royer, 1994, Pellegrino et al., 2013, Raina, 2003, Royer and McNeil, 1991, Webster and Cardé, 1982) factors on the age at which females become sexually mature and on their subsequent calling behaviour.

Most published research examining the factors affecting diel and seasonal patterns of pheromone communication has concentrated on multivoltine species, and there is clear evidence that considerable within species flexibility exits as a result of marked inter-generational differences in ecological conditions. In contrast, the level of flexibility in pheromone communication response to different biotic and abiotic factors by univoltine species has not been as intensely studied.

Western bean cutworm (WBC) Striacosta albicosta (Smith) (Lepidoptera: Noctuidae), is native to western United States but during the past decade this pest has expanded its range eastward and now occurs in States and Provinces in the Great Lakes region (Baute, 2009, Michel et al., 2010). Despite the fact that pheromone traps have been used to monitor range expansion (T. Baute, personal communication), very little is known about pheromone mediated mating of WBC. Therefore, we examined the effect of temperature and relative humidity (RH) on sexual maturation and subsequent calling behaviour of virgin females not only adding to our knowledge of the reproductive biology of this species, but using the WBC as a model system to examine the flexibility of calling behaviour of univoltine species with a mid-summer flight period.