Browsing by Author "He, Xiong Zhao"
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- ItemReproductive behaviour of Aphidius ervi Haliday (Hymenoptera: Aphidiidae : a thesis presented in partial fulfi[l]ment of the requirements for the degree of Doctor of Philosophy in Plant Science (Entomology) at Massey University, Palmerston North, New Zealand(Massey University, 2008) He, Xiong ZhaoAphidius ervi Haliday is a cosmopolitan parasitoid species of several major aphid pests on economically important crops. Prior to this research, little information was available on its reproductive behaviour. Emergence of A. ervi peaks during the first few hours of the photophase with males being protandrous. Females become sexually mature earlier than males and oviposit primarily in the photophase. Aphids parasitised in their early instars die before reproduction but those parasitised in later instars produce a limited number of progeny. Females prefer aphids of 3- to 5-d-old over the younger and older aphids for oviposition. Females ovipositing in 4- to 7-d-old aphids have more fitness gains in terms of progeny body size and egg load at emergence. Fertilised eggs are more likely deposited in large hosts and unfertilised eggs in small ones. Large individuals have greater longevity, large males father more progeny, and large females have higher fecundity, parasitism and greater ability in host searching. However, with increasing body size females gain more than males in longevity and fecundity but males gain more than females in the number of female progeny. Males can inseminate up to nine females and they carry about 82% effective sperm at emergence and replenish about 18% sperm during their adult life. Females adjust the oviposition and sex allocation strategies in response to increasing host density with higher number of aphids parasitised at higher host densities and lower proportion of female progeny produced at lower host densities. Males play an active role in mating behaviour. Males having mating experience, and being large or younger, respond to females more quickly and perform better courtships resulting in higher mating success. Males prefer larger and younger females for mating probably because the latter have greater reproductive potential. Males optimize the use of their sperm based on the availability of their sperm and the reproductive status (age) of females. The switchingoff of female receptivity of male mating attempt after the mating is a gradual process. Some females accept the second males within 1 minute since the termination of the first mating. The shorter mating period in the second mating suggests that females remate probably due to the gradual process of switching-off of female receptivity rather than the insufficient sperm transformation during the first mating. Males prolong their mating duration in male-biased operational sex ratio to reduce the probability of female remating.
- ItemReproductive performance of a spider mite Tetranychus ludeni Zacher (Acari: Tetranychidae) in response to social environments : a thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Entomology at Massey University, Palmerston North, New Zealand(Massey University, 2023) Weerawansha, AgampodiAnimals are sensitive to changes in social environments and may plastically adjust their life history traits in response to multiple socio-environmental factors. Population size and density are two key socio-environmental factors affecting female reproductive output and offspring sex ratio. However, previous studies have mostly focused on only one factor at a time, ignoring the other and their interactions. Moreover, the reproductive plasticity of females in response to social environments has been investigated under constant population size and density, but whether they could adjust their reproductive strategies in response to the fluctuations or shifts of population size and density during the breeding period is largely unknown. Using a haplodiploid spider mite, Tetranychus ludeni Zacher, I carried out a series of experiments to examine how ovipositing females alter their reproductive investment under different population sizes and densities. Results demonstrate that both population size and density and their interaction significantly affected reproduction and sex allocation. I reveal that when the population was small, females tended to reduce local mate competition among sons by producing more daughters. When the population was large and dense, females were more likely to reduce local resource competition by producing more daughters early in life that would disperse from the natal patch to found new colonies. My findings show that the extremely high female-biased offspring sex ratios in large populations could not be explained by local mate competition models alone, and local resource competition and local resource enhancement might also be involved in sex allocation of T. ludeni. However social environments had weaker effects on T. ludeni sex allocation compared to the life history traits, and social environments influencing offspring sex ratio was implemented or mediated through other life history traits. T. ludeni females adjusted their reproductive strategies in response to the shifts of population density and size during their breeding period. Females constrained fecundity in response to the fluctuating environments. Females traded off egg number for size in response to dynamics of population size and increasing egg size significantly raised the proportion of daughters. They fertilized more larger eggs laid in a small population but fertilized more smaller eggs laid in a large population by lowering the egg size dependent fertilization threshold. This study provides evidence that spider mites can manipulate their reproductive output and adjust offspring sex ratio in response to various static and dynamic social environments.