Effect of age, mating history and temperature on male reproductive costs in the bean beetle Callosobruchus maculatus

Abstract

Temperature and humidity determine seed viability, but their effect on seed pest reproduction, such as that of the bean beetle Callosobruchus maculatus, remains understudied. Adult male C. maculatus pass large ejaculates to mates while not feeding. Here, we studied ejaculate production and longevity in C. maculatus males at different temperatures and mating patterns. After development at 25, 27 and 29 °C, eclosing males were weighed and prevented from mating (m0) or allowed to mate once with virgin females three (m3) or five (m5) days after eclosion or to mate twice, three and five days after eclosion (m3+5). We weighed males before and after mating to estimate body mass loss due to ejaculate transfer and depletion of resources over time attributed to routine physiology/evaporation. Warmer conditions increased mortality and development rates and tended to decrease body mass. Males with a large body mass at eclosion survived longer than smaller males. The body mass of males was depleted at daily rates equal to 3–5% of body mass at eclosion. The rates of this loss increased in warmer conditions, suggesting that this process was the main determinant of the thermal pattern of mortality. During a single mating, males produced ejaculates that constituted 2–6% of their body mass at eclosion. Contrary to predictions, ejaculate production did not change with thermal conditions. Body mass losses through ejaculate transfer resulted in increased male mortality, and this effect was two times stronger than the effect of a comparable body mass loss through routine physiology/evaporation. Ejaculate mass decreased with age independent of mating history, suggesting that ejaculate production is restricted by routine physiology/evaporation losses. We conclude that the longevity of male C. maculatus is a function of body mass loss, but the two sources of body mass loss considered here, ejaculates and routine physiology, are not equally costly.