Influence of temperature on female reproductive traits of the armyworm (Lepidoptera: Noctuidae).

Abstract

The armyworm, Mythimna unipuncta (Haworth), is a seasonal migrant that travels every spring from the United States towards northern breeding areas, such as Quebec (Canada), to avoid hot summer temperatures. Because of climate change, it could arrive earlier in the province, and the temperatures encountered upon arrival could increasingly vary, possibly influencing the female's reproductive traits. To explore the influence of temperatures on the reproduction and fecundity of M. unipuncta, we investigated the correlation between the number of eggs in egg clusters and their mass (g). Next, sexually mature couples were formed and subjected to constant temperatures of 10, 17, or 25 °C in growth chambers. We evaluated the lifetime fecundity, daily fecundity, delay between couple formation and egg laying, oviposition period (number of days between the first and last days of oviposition), number of oviposition days inside the oviposition period, mating percentage, and lifetime mating frequency. Our results showed that high temperature (25 °C) reduced egg size. Although temperature did not influence the lifetime fecundity of M. unipuncta, high temperature negatively influenced the couples' mating percentage and frequency. The 25 °C treatment also shortened the females' oviposition period. Together, our findings suggest that high temperatures would be more detrimental to the reproductive parameters of M. unipuncta than cooler temperatures. Results are discussed in a context of climate change.