Studies on the regulation of progeny production and sex-ratio of Wesmael
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Date
1979
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Department of Agricultural Entomology, College of Horticulture,Vellanikkara
Abstract
The fecundity, progeny production, female – male composition of the progeny and duration of development of Bracon brevicornis wesmael as influenced by the density and size (weight) of host larvae of Corcvra cephalonica Stainton and the sex-ratio of the parent parasite population were studied at three temperature- humidity (TH) combinations, viz, 280c and 75% RH (TH1), 300c and 60% RH (TH2) and 320c and 50% RH (TH3).
The maximum fecundity of the parasite was registered consistently at all the three TH levels at a host density level of two larvae per female parasite. The exclusive use of light weight larvae (weight range 8 to 10 mg) as hosts produced significantly less number of eggs at the TH1 and TH2 levels, while at the TH3 level the fecundity was maximum when the heavier host larvae (weight range 30 to 35 mg) were used. The parental sex-ratio levels of 2:1 and 3:1 (female:male ) led to the production of higher number of eggs than under the ratios of 1:1, 1:2 and 1:3.
The maximum progeny production in B. brevicornis at the TH1 and TH2 levels was attained under a host density level of two larvae per female parasite. The progeny production was relatively higher at the TH1 and TH2 levels when heavier larvae were exposed for parasitisation. The superiority of the parental sex-ratio of 2:1 (female: male) in the production of higher number of progeny was established at the TH2 and TH3 conditions.
Significant influence of the host larval density on the female progeny production was detected at the TH1 and TH2 levels. The female progeny production was maximum at a host larval density level of two per female parasite at the TH2 combination, while this was found to be the highest at a density level of one larva per female parasite at the TH1 level. Relatively heavier host larvae produced significantly higher number of female offsprings at the TH2 and TH3 combinations. The parental sex-ratio level of 2:1 (female:male) consistently produced maximum number of female progeny.
The influence of host larval density on the proportion of females was pronounced only at the TH3 level and a density level of two laevae per female parasite was found to be better with reference to the production of a higher proportion of females. The sex-ratio of the parent parasite population influenced the proportion of females in the F progeny and a ratio of 1:3 (female:male) produced higher proportion of females at the TH2 and TH3 combinations.
The host larval density, weight of host larvae and the sex –ratio of the parent parasite population exerted significant influence on the duration of development of B. bravicornis.
The feasibility of manipulating the ambient temperature-humidity conditions for maintaining laboratory cultures of B. brevicornis at the maximum possible levels has been discussed
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MSc
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Citation
171007