Title : Variation in plant biochemistry affects acceptance of lupins by the pea aphid
Abstract:
The pea aphid Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae) is globally distributed throughout all temperate regions of the world but it has become an important pest on legumes also in tropical regions of Africa. One of the alternative methods to the use of neurotoxic insecticides is the exploitation of the natural or bred traits that enable plants to defend themselves against herbivores. Plant acceptance by pea aphids depends on the presence of allelochemicals, which are either the chemical markers of its host plant or toxicants in the non-hosts. The aim of the present work was to establish the level of acceptability of all species of lupines that occur in Poland (the wild species Lupinus polyphyllus Lindl. and cultivated lupines of three species: L. albus L., L. luteus L., and L. angustifolius L.) to the pea aphid infestation and determine the effect of cyclitols and alkaloids on aphid behaviour during probing. Basing on EPG (Electrical Penetration Graph) monitoring of the pea aphid behaviour during penetration in plant tissues, we found that aphids did not ingest phloem sap while probing on L. angustifolius and the probes were very short. All varieties of L. angustifolius were rejected by aphids during an early stage of probing in peripheral tissues, i.e., epidermis or mesophyll. On L. polyphyllus and on both studied varieties of L. albus, the probes were short and none of the aphids on these plants reached phloem vessels. It is likely that the rejection of these lupins was caused by chemical factors detected by aphids at the epidermis and mesophyll level. On L. luteus the total and mean duration of probing, time to reach phloem phase, and the duration of the first phloem phase were comparable to those in aphids on control plant Pisum sativum. Eighteen alkaloids were identified: one piperidine alkaloid (ammodendrine), one indole (gramine), ten quinolizidine alkaloids (one tricyclic and nine tetracyclic compounds), and six esters. All lupine varieties that contained lupanine, its derivatives and especially their esters appeared to be unacceptable to the pea aphid, independent of the total concentration of any specific lupanine alkaloid. In contrast, sparteine and its derivatives did not seem to affect aphid probing significantly. The following cyclitols were found in lupine species: myo-inositol, D-ononitol, and D-pinitol. L. angustifolius also contained D-chiro-inositol. Cyclitols had no significant effect on aphid probing and feeding and lupin susceptibility to the pea aphid infestation.
