Reproduction
C. maculatus mating is injurious for the female. The male possesses penile spines and these cause damage to the female reproductive tract. Females forcefully kick the males during copulation, which serves to end the mating event. It is possible that male beetles benefit from harming females because the injury to the female could cause reduced mating or mating success with other males, or increased egg-laying in the injured female. When females are prevented from kicking the males (by removal of the hind legs), matings continued for longer than usual, and harm to females was increased. However, the amount of time before females became receptive to mating again and the rate of oviposition were not affected. This suggests that penile spines do not increase the reproductive success of males, and biologists have speculated that the spines do not increase reproductive success for either sex, and may have no adaptive value.
Once the female has mated with a male, whose donation of spermatophores (capsule containing nourishment and sperm) can be up to 20% of his body weight, she glues single eggs to the chosen bean. Females generally lay fewer eggs when there are fewer hosts. In an experimental set-up, females that were presented with three large beans laid more eggs than females presented with three small beans. Occasionally females deposit many eggs onto nonviable surfaces, especially if there are few or no hosts available. This leads to a higher mortality rate in eggs and potential larvae, but it may also lead to host expansion in the long term.
Read more about this topic: Callosobruchus Maculatus
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