THE ROLE OF ALTERNATIVE HOST-PLANT SPECIES IN THE LIFE OF A POLYPHAGOUS MOTH, OPEROPHTERA BRUMATA (LEPIDOPTERA: GEOMETRIDAE)

SUMMARY (1) As a major determinant of larval winter moth population levels is known to be the degree of synchrony between larval eclosion and the bud burst of the primary host-plant, the oak, it is argued that two hitherto unstudied factors have a considerable effect on the insects' population dynamics. These are: (a) the events occurring immediately after eclosion and the effect of the period of food deprivation which occurs should no food be available locally; (b) the degree to which larvae can utilize food-plant species other than the primary host. (2) Experimental evidence is presented which shows that first instar larvae can discriminate between host-plant species, and that this is unaffected by the degree of food deprivation relevant to field conditions. Also, it is shown that early deprivation has little if any adverse affects on the subsequent growth and development of larvae, and that it may confer mild advantages. (3) A comparison is made of the development of larvae reared on primary and alternative hosts before, during and after the period of peak level eclosion and oak bud burst in the field. Four of the five alternative food-plant species tested are found to support satisfactory larval growth. Further, it is only during the period of maximum oak bud burst that an oak diet results in a considerably greater reproductive success than that supported by a diet of alternative hosts. (4) It is argued that the polyphagy of winter moth larvae is a mechanism which promotes synchrony of larval eclosion with the primary host plant. It is also associated with several unusual features of winter moth biology; in particular the larval, as opposed to adult host selection and dispersal, as well as increased adult fecundity. SUMMARY (1) As a major determinant of larval winter moth population levels is known to be the degree of synchrony between larval eclosion and the bud burst of the primary host-plant, the oak, it is argued that two hitherto unstudied factors have a considerable effect on the insects' population dynamics. These are: (a) the events occurring immediately after eclosion and the effect of the period of food deprivation which occurs should no food be available locally; (b) the degree to which larvae can utilize food-plant species other than the primary host. (2) Experimental evidence is presented which shows that first instar larvae can discriminate between host-plant species, and that this is unaffected by the degree of food deprivation relevant to field conditions. Also, it is shown that early deprivation has little if any adverse affects on the subsequent growth and development of larvae, and that it may confer mild advantages. (3) A comparison is made of the development of larvae reared on primary and alternative hosts before, during and after the period of peak level eclosion and oak bud burst in the field. Four of the five alternative food-plant species tested are found to support satisfactory larval growth. Further, it is only during the period of maximum oak bud burst that an oak diet results in a considerably greater reproductive success than that supported by a diet of alternative hosts. (4) It is argued that the polyphagy of winter moth larvae is a mechanism which promotes synchrony of larval eclosion with the primary host plant. It is also associated with several unusual features of winter moth biology; in particular the larval, as opposed to adult host selection and dispersal, as well as increased adult fecundity. SUMMARY (1) As a major determinant of larval winter moth population levels is known to be the degree of synchrony between larval eclosion and the bud burst of the primary host-plant, the oak, it is argued that two hitherto unstudied factors have a considerable effect on the insects' population dynamics. These are: (a) the events occurring immediately after eclosion and the effect of the period of food deprivation which occurs should no food be available locally; (b) the degree to which larvae can utilize food-plant species other than the primary host. (2) Experimental evidence is presented which shows that first instar larvae can discriminate between host-plant species, and that this is unaffected by the degree of food deprivation relevant to field conditions. Also, it is shown that early deprivation has little if any adverse affects on the subsequent growth and development of larvae, and that it may confer mild advantages. (3) A comparison is made of the development of larvae reared on primary and alternative hosts before, during and after the period of peak level eclosion and oak bud burst in the field. Four of the five alternative food-plant species tested are found to support satisfactory larval growth. Further, it is only during the period of maximum oak bud burst that an oak diet results in a considerably greater reproductive success than that supported by a diet of alternative hosts. (4) It is argued that the polyphagy of winter moth larvae is a mechanism which promotes synchrony of larval eclosion with the primary host plant. It is also associated with several unusual features of winter moth biology; in particular the larval, as opposed to adult host selection and dispersal, as well as increased adult fecundity. SUMMARY (1) As a major determinant of larval winter moth population levels is known to be the degree of synchrony between larval eclosion and the bud burst of the primary host-plant, the oak, it is argued that two hitherto unstudied factors have a considerable effect on the insects' population dynamics. These are: (a) the events occurring immediately after eclosion and the effect of the period of food deprivation which occurs should no food be available locally; (b) the degree to which larvae can utilize food-plant species other than the primary host. (2) Experimental evidence is presented which shows that first instar larvae can discriminate between host-plant species, and that this is unaffected by the degree of food deprivation relevant to field conditions. Also, it is shown that early deprivation has little if any adverse affects on the subsequent growth and development of larvae, and that it may confer mild advantages. (3) A comparison is made of the development of larvae reared on primary and alternative hosts before, during and after the period of peak level eclosion and oak bud burst in the field. Four of the five alternative food-plant species tested are found to support satisfactory larval growth. Further, it is only during the period of maximum oak bud burst that an oak diet results in a considerably greater reproductive success than that supported by a diet of alternative hosts. (4) It is argued that the polyphagy of winter moth larvae is a mechanism which promotes synchrony of larval eclosion with the primary host plant. It is also associated with several unusual features of winter moth biology; in particular the larval, as opposed to adult host selection and dispersal, as well as increased adult fecundity.