Aphid feeding, as influenced by disruption of the symbiotic bacteria: an analysis of the pea aphid ( Acyrthosiphon pisum)

Abstract

Pea aphids ( Acyrthosiphon pisum) whose symbiotic bacteria were disrupted with the antibiotic chlortetracycline over the first 5 days after birth (i.e. aposymbiotic aphids), were able to feed from the host plant Vicia faba, as indicated by the regular production of honeydew droplets and by electrical penetration graph (EPG) recordings of stylet penetration through the plant tissues to the sieve elements. No difference was identified in the time taken by adult symbiotic and aposymbiotic aphids [24 ± 2.4 and 24 ± 3.0 min (mean ± SE), respectively] to penetrate the plant tissues and puncture the sieve elements during the probes which resulted in sustained phloem feeding. 7/8-day-old aposymbiotic larvae produced less honeydew (0.43 ± 0.038 mg/aphid) over 24 h than symbiotic aphids (0.79 ± 0.079 mg/aphid), but this difference was attributed primarily to the greater body size of the symbiotic aphids, suggesting that feeding by these larval aphids was not substantially impaired. The aposymbiotic larvae produced smaller honeydew droplets more frequently than symbiotic larvae, and no difference between the number of droplets produced in the first and second 12 h in the 24 h recording period was found. Aposymbiotic adults, in contrast, fed relatively poorly. Both EPG and honeydew production studies indicated that all symbiotic adults, but only 60–66% of aposymbiotic adults, had initiated phloem ingestion within a 10 h test period. It is proposed that the deleterious effects of bacterial disruption may be cumulative, and become increasingly severe and nonspecific with time since antibiotic treatment. It is recommended that studies on the nutritional physiology of aposymbiotic aphids are conducted with recently-generated aposymbionts, whose feeding responses are not impaired.