The susceptibility of verieties of carrot to attack by the aphid, Cavariella aegopodii (Scop.)

Representative varieties from the carrot groups, Chantenay, Nantes, Berlikum and Autumn King, together with three Australian varieties, were tested for susceptibility to attack by Cavariella aegopodii (Scop.). Tests were done at different average temperatures in cages in the insectary by inoculating plants with apterous forms of the aphid and frequently checking the extent of colonization over the next 20 or so days. Field sowings of the varieties were also made in each of 3 years, and over the immigration period and the subsequent population development and decline of the aphid, regular counts were made of the alates settling on a standard number of plants of each variety, and of the progeny produced. Some differences in susceptibility to attack were noted but, because the main development of C. aegopodii on field carrots is limited to two generations, these were too small to be of practical value in terms of plant resistance, and on all varieties large numbers of aphids could be found. Although the Australian variety Osborne Park was thought to have some resistance to C. aegopodii in New Zealand, it proved to be of average susceptibility. Autumn King appeared to be the most aphidsusceptible variety but could be tolerant to motley dwarf virus. Nantes was not as tolerant to aphid attack as the other varieties and as it is also intolerant to motley dwarf virus, might suffer much damage in years favouring aphid expansion. Berlikum seemed to be the least susceptible to aphid attack. Temperature differences affected expressions of varietal susceptibility less than they affected aphid fecundity and a few degrees increase in temperature more than halved the number of young born in a generation.