Multiple mating and mate choice in Sitophilus oryzae (L.) (Coleoptera : Curculionidae) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Plant Protection (Entomology) at Massey University, Palmerston North, New Zealand
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Date
2010
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Massey University
Abstract
The rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae) is a major pest
of stored grains throughout the world. A recent study found a reduction in fecundity
and fertility in females that are exposed to multiple males. However, the mechanism
behind this is unknown. In the first experiment we examined female S. oryzae fitness
decline and behaviour in response to male density (i.e. 1, 5 and 10 males) maintained
with a single female. Results show that female fecundity and longevity significantly
decreased with increased male density (P < 0.01). However there was no significant
effect of male density on fertility. Mating time significantly increased with male
density (P < 0.01) but feeding and foraging time decreased from male density 1 to
male density 5 and 10 (P < 0.03). The decrease in fecundity under high male density
is proposed to be caused by increased damage by male reproductive organs. The
second experiment examined precopulatory sexual selection in S. oryzae. Results
show that both sexes select for large genitals. In addition males select for the number
of mature eggs in females. These traits may directly affect the reproductive fitness of
these insects. In the final experiment we examined how multiple mating affected
female reproductive fitness in the laboratory. Results indicate that over sixty days
females permanently paired with males, mated twice with different males and four
times with the same males did not suffer from significant fertility decline while
females mated once, twice with the same males and four times with different males
had significant fertility declines. It is suggested that mating once or twice with the
same males is not enough for females to maximise their reproductive fitness. The
significant fertility decline in females that mated with four different males may be
caused by reproductive organ damage or other factors which decreases their fertility
due to excessive polyandry.
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Keywords
Rice weevil, Sitophilus oryzae, Rice weevil fertility, Multiple mating, Oviposition