Ecology of Coleophora spissicornis (Haworth) and C. frischella (Linnaeus) associated with Trifolium repens Linnaeus in Canterbury, New Zealand

Abstract

This thesis reports the first comprehensive ecological study on a population of Coleophora spissicornis and C. frischella infesting Trifolium repens. The study was conducted at Lincoln, New Zealand during the summer seasons from 1969/70 to 1971/72. The biology of the two species and sampling methods for them were investigated during the first two seasons, and quantitative sampling was conducted during the third season.

No characters were found which could be used to differentiate between the two species during the egg and early larval instars. They occupy the same niche in time and space. Females place their eggs into a cavity beside the hinge in white clover florets and larvae eat developing seeds.

The lower threshold temperatures for development of eggs are 12.9 C for C. spissicornis and 12.8 C for C. frischella; the developmental rates are identical, eclosion occurring after 6.7 days at 20 C. The developmental rates of the larval instars are also similar. The lower developmental threshold temperature for C. spissicornis pupae is 11.7 C and development is completed in 14.5 days at 20 C.

No major differences in the behaviour of the larval or adult instars were found.

There are major differences in voltinism and fecundity. C. spissicornis is univoltine while the C. frischella population is composed of univoltine and multivoltine strains. The mean number of eggs deposited by a C. spissicornis female during its 5.7 day life was 17.2 but a C. frischella female deposited 59.8 over 9.7 days.

The heaviest mortality occurs during the final larval instar, both before and after feeding is completed. Mortality during this instar, in decreasing order of impact, is caused by an unidentified "disease", two pathogenic fungi (Beauvaris sp. and Paecilomyces sp.), a parasitic wasp, Bracon variegator, a Pyemotes sp. mite, and intrapopulation competition. Competition gives rise to the heaviest mortality during the earlier instars; the disease is also present but the parasites are not. Competition and B. variegator do not affect larvae on the soil surface.

Searching was found to be costly but the only practicable method for extracting Coleoehora spp. from their habitats. At the population levels encountered the most efficient sampling units were one half of axially divided flowers and 50 cm² quadrats of surface soil and litter. Components of variance showed that variance among flowers accounts for more than 85% of the variation in this habitat; coefficients of variation were mostly between 70% and 150% but ranged from 40% to 570%. In the litter habitat variance among quadrats is the major variance source; coefficients of variation were lower, with most between 20% and 40%.

A sampling plan for the construction of age-specific budgets is presented.

It is doubtful that studies of the dynamics of Coleophora spp. populations would lead to the development of new control strategies at a reasonable cost. A reduction of their economic impact would more readily be achieved through the introduction of additional parasites or the development of resistant host varieties. This thesis reports the first comprehensive ecological study on a population of Coleophora spissicornis and C. frischella infesting Trifolium repens. The study was conducted at Lincoln, New Zealand during the summer seasons from 1969/70 to 1971/72. The biology of the two species and sampling methods for them were investigated during the first two seasons, and quantitative sampling was conducted during the third season.

No characters ware found which could be used to differentiate between the two species during the egg and early larval instars. They occupy the same niche in time and space. Females place their eggs into a cavity beside the hinge in white clover florets and larvae eat developing seeds.

The lower threshold temperatures for development of eggs are 12.9 C for C. spissicornis and 12.8 C for C. frischella; the developmental rates are identical, eclosion occurring after 6.7 days at 20 C. The developmental rates of the larval instars are also similar. The lower developmental threshold temperature for C. spissicornis pupae is 11.7 C and development is completed in 14.5 days at 20 C.

No major differences in the behaviour of the larval or adult instars were found.

There are major differences in voltinism and fecundity. C. spissicornis is univoltine while the C. frischella population is composed of univoltine and multivoltine strains. The mean number of eggs deposited by a C. spissicornis female during its 5.7 day life was 17.2 but a C. frischella female deposited 59.8 over 9.7 days.

The heaviest mortality occurs during the final larval instar, both before and after feeding is completed. Mortality during this instar, in decreasing order of impact, is caused by an unidentified "disease", two pathogenic fungi (Beauvaris sp. and Paecilomyces sp.), a parasitic wasp, Bracon variegator, a Pyemotes sp. mite, and intrapopulation competition. Competition gives rise to the heaviest mortality during the earlier instars; the disease is also present but the parasites are not. Competition and B. variegator do not affect larvae on the soil surface.

Searching was found to be costly but the only practicable method for extracting Coleoehora spp. from their habitats. At the population levels encountered the most efficient sampling units were one half of axially divided flowers and 50 cm² quadrats of surface soil and litter. Components of variance showed that variance among flowers accounts for more than 85% of the variation in this habitat; coefficients of variation were mostly between 70% and 150% but ranged from 40% to 570%. In the litter habitat variance among quadrats is the major variance source; coefficients of variation were lower, with most between 20% and 40%.

A sampling plan for the construction of age-specific budgets is presented.

It is doubtful that studies of the dynamics of Coleophora spp. populations would lead to the development of new control strategies at a reasonable cost. A reduction of their economic impact would more readily be achieved through the introduction of additional parasites or the development of resistant host varieties.