Co-Authors:
Mendel, Z., Department of Entomology and Natural Products, Agricultural Research Organization, The Volcani Center, Bet Dagan, 50250, Israel
Blumberg, D., Department of Entomology and Natural Products, Agricultural Research Organization, The Volcani Center, Bet Dagan, 50250, Israel
Zehavi, A., Forests Department, haKeren haKayemet le'Israel (J.N.F.), Eshta'ol, Israel
Weissenberg, M., Department of Chemistry of Pesticides and Natural Products, Agricultural Research Organization, The Volcani Center, Bet Dagan, 50250, Israel
Abstract:
Interactions were studied among alkaloid-containing legumes (Erythrina corallodendrum and Spartium junceum) and non-toxic plants (Citrus sinensis, Cucurbita moschata and Euphorbia tirucalli), several polyphagous homopterans, Aphis craccivora (Aphididae), Icerya purchasi, I. aegyptiaca (Margarodidae), Lepidosaphes ulmi (Diaspididae) and Planococcus citri (Pseudococcidae), and some major natural enemies of these homopterans. Significant reductions in survival due to negative effects of alkaloid containing as compared with non-alkaloidal plants were recorded for the predators Rodolia cardinalis and Chilocorus bipustulatus, but not for Cryptolaemus montrouzieri (Coleoptera: Coccinellidae), Chrysoperla carnea (Neuroptera: Chrysopidae) and Sympherobius sanctus (Neuroptera: Sympherobiidae). The development time of the larvae or pupae of R. cardinalis, C. carnea and S. sanctus was longer on the toxic plants than on the non-toxic ones. The percentage of parasitism of A. craccivora collected from the non-alkaloidal plants Vicia palaestina and Melilotus albus was much higher than that on S. junceum. The parasitoid complexes of A. craccivora differed between both plant groups. The nutritive value of honeydew of I. purchasi and A. craccivora, as expressed by the life span of Encyrtus infelix (Hymenoptera: Encyrtidae) adults, was also investigated. Life spans were significantly longer when the wasps fed on honeydew produced on non-alkaloidal plants (C. sinensis and Pittosporum tobira) than on alkaloid containing plants when I. purchasi - but not A. craccivora - was the producer. It is suggested that the chemical defense of E. corallodendrum and S. junceum is exploited by polyphagous phytophages to reduce predation. In nature, population growth and density of four of the investigated homopterans are conspicuously high when they developed on the alkaloid containing plant species, and very low on non-alkaloid plants. The efficiency of their natural enemies may be reduced by sequestration of alkaloids (or other toxic plant compounds) or their transfer into excreted honeydew. Therefore it is assumed that a generalist phytophagous homopteran may be protected from its natural enemies, although at different rates of efficiency, if it can safely sequester the host allelochemical when it develops on toxic species within its host range. © 1992 Georg Thieme Verlag Stuttgart.