Influence of host plant condition on population increase ofTetranychus telarius(Linnaeus) (Acarina: Tetranychidae)

Population growth studies were conducted with Tetranychus telarius (Linnaeus) on lima beans in the greenhouse. The capacity of populations to increase was studied in relation to host-plant nutrition, leaf age and plant age. Host-plant nutrition influenced population increase by affecting both longevity and fecundity. Adult female longevity was adversely affected when the mites were confined to plants grown in nutrient solutions deficient in phosphorus, nitrogen or potassium, rather than in full-nutrient solutions. In the host-plant nutrition studies, nitrogen deficiency was most detrimental for survival and phosphorus deficiency least detrimental. Age-specific fecundities were severely reduced when females were confined to plants grown in the deficient solutions. The phosphorus-deficient treatment gave the greatest reduction in total fecundity as well as maximum fecundity attained. This was true for both old and young leaves. The old leaves of the potassium-deficient treatment induced the second greatest reduction in both total and maximum fecundities. The nitrogen-deficient treatment was superior to either mentioned above but significantly inferior to the full-nutrient treatment. The young foliage in the potassium-deficient treatment was somewhat superior to the old foliage in the full-nutrient treatment in both total and maximum fecundities. Mite populations reared on host plants which received a full nutrient supply showed greater net reproduction rates and intrinsic rates of increase. Phosphorus-deficient plants were the most detrimental to these population attributes. The nitrogen-deficient plants and old leaves of the potassium-deficient plants gave intermediate results, while young leaves of the latter gave results comparable to those obtained on old leaves of the full-nutrient treatment. Although leaf age had no effect upon adult survival, young leaves, regardless of nutritional treatment, were more favorable for both total and maximum fecundities. Consequently, young leaves enhanced population growth in comparison to old leaves. Plant age was also found to affect population increase. Fecundity was reduced on older plants but survival was not affected.