No abstract

The effect of temperature on the life table of Acyrthosiphon pisum reared on Pisum sativum was evaluated under laboratory conditions using temperatures of 10, 15, 20, 25, 30, and 35°C. The development time of juvenile A. pisum decreased with increasing temperature (from 21.3 days at 10°C to 4.7 days at 35°C). Adult longevity also decreased with increasing temperature (from 53.2 days at 10°C to 2.3 days at 35°C). Interestingly, 70% and 25% of A. pisum nymphs reared at 30°C and 35°C, respectively, successfully developed into adults. These temperatures have previously been considered unsuitable for A. pisum development. However, adult aphids reared at 30°C and 35°C failed to reproduce. Linear regression analysis revealed that the lower development threshold of A. pisum was 153.1 degree-days above 1.9°C. Maximal average reproductive capability was observed at 10°C for A. pisum adults, with each adult producing more than 120 nymphs. The intrinsic rate of increase (rm) of A. pisum increased from 0.124/day at 10°C to 0.337/day at 25°C, whereas opposite trends were observed for the net reproductive rate (R0) and the mean generation time (GT). At 20°C and 25°C, the intrinsic rate of increase of A. pisum was significantly higher than at 10°C and 15°C (P < 0.0001), indicating that 20°C and 25°C are within the optimal range for the growth of A. pisum, and that 30°C is beyond the upper threshold limit for reproduction, which involves a temperature range that is narrower than that of the survival range (upper limit is unknown, but above 35°C).

In aphids, an identification system based on adult morphology is difficult to apply to larvae or adults of a different morph because of their small size and extensive polymorphism. In this work, identification of aphids using random amplified polymorphic DNA (RAPD) fingerprinting to generate species-specific primers was studied. A total of 20 RAPD primers were screened on eleven members of Aphidinae, i.e., Acyrthosiphon pisum, Aphis craccivora, Aphis gossypii, Aphis rumicis, Cavariella salicicola, Indomegoura indica, Lipaphis erysimi, Myzus formosanus, Myzus hemerocallis, Myzus persicae, and Toxoptera odinae. DNA fragments potentially useful as species-specific markers were selected for six aphid species. A primers set, A02ApF/A02ApR, based on the nucleotide sequence of a specific 462 bp fragment obtained from Ac. pisum by RAPD-PCR using primer A02, amplified this fragment only from Ac. pisum genomic DNA, but not from that of other species. The specificity of the primers for M. persicae was further confirmed using individuals from several field populations. It is concluded that RAPD PCR-SCAR (sequence characterized amplified region) DNA assay is a useful method for the detection of species-specific DNA fragments in mixed populations, and that pertinent data could facilitate development of a realistic quarantine system for pea aphids.