Theories predict that in polyandrous species, the focal male should increase sperm allocation per mate in the presence of rivals to gain greater share of paternity, but in the presence of additional mates, he should reduce sperm allocation per mate to save sperm for insemination of more mates. However, empirical findings are often inconsistent and reasons behind are unclear. Furthermore, many studies use copulation duration as an estimate of the number of sperm transferred. Yet, empirical evidence for such assumption is largely lacking. Here, we used a sperm heteromorphic insect Ephestia kuehniella whose males produce two types of sperm, eupyrenes (fertile) and apyrenes (nonfertile), to test these postulations. We allowed focal males to detect chemical and acoustic but no tactile cues from rivals or additional mates both before and during mating and measured copulation duration and sperm allocation in successive copulations. We demonstrate that males transfer significantly more eupyrenes per mate in the presence of rivals and that the sperm allocation pattern persists in successive copulations under this condition. However, males do not adjust apyrene allocation in response to rivals probably because apyrenes play a relatively minor role in male reproductive success. Contrary to a previous study, focal males do not respond to additional mates most likely due to the lack of tactile cues in the present study. We reveal that sperm allocation is not a function of copulation duration in this insect for spermatophore formation and delivery occupy most of copulation duration and sperm transfer is complete near the end of copulation.

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Theory predicts that due to limited resources males should strategically adjust their investment in reproduction and survival. Based on different conceptual framework, experimental designs, and study species, many studies support while others contradict this general prediction. Using a moth Ephestia kuehniella whose adults do not feed and thus have fixed resources for their lifetime fitness, we investigated whether males adjusted their investment in various life activities under dynamic socio-sexual environment. We allowed focal males to perceive rivals or additional females without physical contact. We show that males do not adjust the number of sperm they transfer to mates in a given copulation at different immediate or both immediate and mean sperm competition levels. Contradictory to general predictions, our results demonstrate that cues from additional females increase males' investment in courtship and reduce their lifetime number of copulations and sperm ejaculated, whereas cues from rivals have no effect on these parameters. Males have similar longevity in all treatments. We suggest that the sex pheromone produced by multiple females overstimulate males, increasing males' costly flirtations, and reducing their lifetime copulation frequency and fecundity. This finding offers a novel explanation for the success of mating disruption strategy using sex pheromones in pest management.

Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say), is the most important insect pest of potato in Iran. If local potato varieties vary in susceptibility to the pest, host plant resistance may provide management benefits to potato growers. A life table study was carried out to determine the relative suitability of four common potato varieties (Agria, Marfona, Savalan and Satina) for CPB development and reproduction in northwest Iran under laboratory conditions at 23 ± 3 ºC, 62 ± 10% RH, and natural photoperiod. Development time and hence generation time was longest on Savalan (31.07 ± 0.48 d and 42.72 ± 0.71 d respectively) and shortest on Agria (27.8 ± 0.65 d and 35.99 ± 0.8 d respectively). Juvenile mortality was highest (47.5%) on Satina and lowest (22.5%) on Marfona. Intrinsic rates of increase (r) were 0.129 ± 0.005, 0.127 ± 0.005, 0.129 ± 0.006 and 0.104 ± 0.004, on Agria, Marfona, Satina and Savalan, respectively, that on Savalan being significantly lower than the others. The highest net reproductive rate was 145.26 ± 25.23 on Marfona and the lowest was 81.18 ± 2.71 on Savalan which was not significantly different among the cultivars. It seems that, among the four tested cultivars, the Savalan cultivar is less suitable to CPB, resulting in the poorest overall biological performance of the beetle, but the level of resistance did not appear sufficient to negate the need for other control methods.