Some polyphagous Homoptera gain protection from their natural enemies by feeding on the toxic plantsSpartium junceum andErythrina corallodendrum (Leguminosae)

Abstract

SummaryInteractions were studied among alkaloidcontaining legumes (Erythrina corallodendrum and Spartium junceum) and non-toxic plants (Citrus sinensis, Cucurbita moschata and Euphorbia tirucalh), several polyphagous homopterans, Aphis craccivora (Aphididae), Icerya purchasi, L 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 L 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 L purchasibut 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 (of 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 fange.

Food Relationships

“…The prey were reared on the alkaloid -bearing legumes Erythrina corallodendron and Spartium junceum and on non -toxic plants as a control. Survival of both ladybirds was signifi cantly reduced and the development time of R. cardinalis increased by preying on insects from the toxic plants (Mendel et al 1992 ). However, this was not the case with Cryptolaemus montrouzieri .…”

Insect‐resistant transgenic plants in a multi‐trophic context

“…Negative effects of host plant resistance on carnivores may be found when herbivores sequester plant toxins and subsequently employ them in their defence against their carnivorous enemies (Barbosa, 1988; Björkman and Larsson, 1991; Mendel et al ., 1992; Pasteels et al ., 1988; Peterson et al ., 1987). This may especially occur in specialist herbivores (Dicke, 1999).…”

A case of ecological specialization in ladybirds:Iberorhyzobius rondensis(Coleoptera: Coccinellidae), potential biocontrol agent ofMatsucoccus feytaudi(Hemiptera: Matsucoccidae)

“…The specialist R. cardinalis was tested on 16 prey species before its introduction in Galapagos and it was only able to complete its life cycle with one, Margarodes similis Morrison which, like the target prey I. purchasi , belongs to the family Monophlebidae (Causton et al , 2004). According to Hodek & Honěk (1996) most cases of unsuitable prey concern herbivores that derive chemical protection from their toxic plants (e.g., Mendel et al , 1992).…”