The cowpea aphid,
Aphis craccivora
Koch (Aphididae), is considered to be one of the major pests in the semiarid Pampas
of Argentina and in other alfalfa (
Medicago sativa
L.) growing areas of the world. In the present study the antibiotic,
antixenotic, and tolerance resistance of eight alfalfa cultivars to
A. craccivora, were investigated under laboratory
conditions at 24 ± 1 °C, 65 ± 10% relative humidity, and 14:10 h photoperiod. Antibiosis experiments showed significant
differences in the developmental time and adult longevity of the cowpea aphid among the alfalfa cultivars. Intrinsic rate
of natural increase (r
m) for apterous aphids varied significantly with alfalfa cultivars on which aphids were reared. This
value ranged from 0.04 to 0.16 females female
-1 d
-1, which was the lowest on ‘Medina’. Additionally, the estimated net
reproductive rate (R
0) and finite rate of increase (λ) for apterous aphids were the lowest on ‘Medina’. For the antixenosis
experiment significant difference was found in aphid’s preference to the alfalfa cultivars. ‘Carmina’ and ‘Victoria’ were the
least preferred by the apterous aphids. For the tolerance experiment ‘Carmina’, ‘Monarca’, ‘SPS6550’ and ‘Victoria’ were
more tolerant than the other cultivars to
A. craccivora. Therefore, our results demonstrated that among the investigated
cultivars ‘Medina’ displayed antibiosis to
A. craccivora, ‘Carmina’ and ‘Victoria’ expressed antixenosis and tolerance, and
‘Monarca’ and ‘SPS6550’ were tolerant to this aphid pest.
