Sex ratios of Coccophagus atratus compere (Hymenoptera:Aphelinidae) in relation to host availability
- Authors: Donaldson, John Sydney
- Date: 1985
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5632 , http://hdl.handle.net/10962/d1004933
- Description: The mode of sex determination in most Hymenoptera is that of arrhenotokous parthenogenesis, i.e. females originate from fertilised eggs and males develop parthenogenetically from unfertilised ones. Females can therefore determine the sex of each of their offspring by controlling fertilisation. This has led to much speculation about the factors that govern hymenopteran sex ratios. Many sex ratio theories predict that solitary Hymenoptera should produce male and female offspring in a ratio of 1:1. The limited data available on sex ratios in solitary Hymenoptera does not support this prediction. However, for various reasons, data may not be representative and few detailed studies have been done. The purpose of this study was, therefore, to examine sex ratios of Coccophagus atratus, a solitary hymenopteran parasitoid, to determine whether sex ratios in this species approach 1: 1. C. atratus is a suitable species for sex ratio studies because male and female eggs are deposited in different hosts. The sex of deposited eggs can, therefore, be determined at oviposition. This eliminates any possible effects of differential mortality. Laboratory experiments were designed to determine whether C. atratus females deposit male and female eggs in fixed proportions or in a set sequence. In addition, samples of hosts were collected from the field to assess C. atratus sex ratios under natural conditions. Results show that C. atratus females do not produce sex ratios that approach 1:1 and male and female eggs are not deposited in a set sequence. Sex ratios are variable and appear to be related to the relative abundance of hosts suitable for female development and for male development. These results are discussed in relation to current sex ratio theories.
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- Date Issued: 1985
The host-searching behaviour of coccophagus atratus compere (Aphalinidae: hymenoptera)
- Authors: Clark, Maxwell Maitland
- Date: 1985
- Subjects: Coccophagus , Hymenoptera , Insects -- Host plants , Insect-plant relationships
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5630 , http://hdl.handle.net/10962/d1004923 , Coccophagus , Hymenoptera , Insects -- Host plants , Insect-plant relationships
- Description: The host-searching behaviour of the parasitoid Coccophagus atratus Compere was investigated. C. atratus parasitoids have unusual host relationships. Female offspring develop in scale insects but male offspring develop hyperparasitically on their conspecific females, or on other parasitoid species. C. atratus females, therefore, must locate, identify and oviposit into two different types of hosts. A primary aim of this thesis, was to identify when and how the behaviour of a female, searching for hosts suitable for female offspring, differed from that of a female searching for hosts suitable for male offspring. This was done by investigating and comparing the behaviour of virgin and mated females. Virgin females can lay only male eggs while mated females can lay both male and female eggs. The role of plant odours and host odours in attracting C. atratus females to the host habitat and to their scale insect hosts was examined with the aid of an olfactometer. Field observations, to test the validity of results obtained in laboratory experiments, indicated that C. atratus females do not search initially for for their hosts' food plants, but search directly for hosts. Only when hosts were physically located did the behaviour of virgin and mated females differ. Recognition cues used by the females to distinguish between the two types of hosts were identified. Finally, the implications of results obtained were discussed in relation to ecological and evolutionary aspects of heteronomous parasitoid biology.
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- Date Issued: 1985