Soldiers of a European gall aphid,Pemphigus spyrotecae (Homoptera: Aphidoidea): Why do they molt?

Abstract

Abstract-A non-migratory aphid, Pemphigus spyrothecae, produces l st-instar larvae of 2 types in the gall: thick-legged ones and normal-legged ones. It was found that the thick-legged larvae play a defensive role, hence they may be called soldiers. Unlike the soldiers of other species hitherto reported, at least some soldiers of this species molt and become adults. Their incomplete sterility is explained historically:1) The migratory ancestor of P. spyrothecae once produced monomorphic l st-instar larvae attacking predators in the gall. 2) It acquired a non-migratory life cycle by the larviposition of emigrants in the gall. 3) As a result, lst-instar larvae of another morph, which had lived on the secondary host without attacking predators, joined the gall inhabitants. This hypothesis is supported strongly by the fact that the normal-legged lst-instar larvae very much resemble the lst-instar larvae of migratory Pemphigus species produced on the secondary hosts.

Pemphigus “soldiers” and a defence of the generation-packing hypothesis: A response to Itô and Akimoto

“…We proposed that the non-migratory life cycles of these Pemphigus species have evolved through generation packing (GP): in the migratory ancestor of a non-migratory Pemphigus species a mutation that caused alate .emigrants to Iarviposit in the gall (instead of on the secondary host) occurred and was fixed, and the "emigrants" were later transformed into apterae. Morphological data for P. spyrothecae (Aoki & Kurosu 1986) and P. monophagus (Aoki & Kurosu 1988a) accord well with what the GP hypothesis predicts.As a result of GP, 2 types of (lst-instar) larvae coexist in the gall of a non-migratory species. Larvae of one type are original gall inhabitants, and those of the other type had once lived on the secondary host, and were packed into the gall.…”

“…However, neither P. spyrothecae nor P. monophagus has such intermediate-like lst-instar larvae (Aoki & Kurosu 1986, 1988a.…”

Ecological factors promoting the evolution of colony defense in aphids: computer simulations

“…Aoki (1978) and Aoki and Kurosu (1986) found that fertile defensive larvae appear in the galls of Pemphigus dorocola and P. spyrothecae. Heie (1980) and Aoki and Kurosu (1988b) reported that the colonies of both species last much longer than those of other Pernphigus species without defenders (for P. dorocola, from early July to November; for P. spyrothecae, as late as November).…”

New records of aphid species (Hemiptera: Aphididae) in Greece

“…The species is monoecious holocyclic and winged sexuparae emerge in AugustNovember to produce sexuals on the bark of the trees (Lampel 1960). First instar nymphs with thick forelegs function as soldiers and defend the gall against predators (Aoki andKurosu 1986, Foster 1990), repair the gall (Pike and Foster 2004) and remove waxcoated droplets of honeydew (Pike et al 2002). The species is widely distributed in Europe, in North Africa (Tunisia), Western Siberia, Pakistan and introduced into Canada [Blackman and Eastop (1994) It is a holocyclic, heteroecious species and the fundatrix makes galls on leaves of P. nigra which originate from the mid-rib at the base of the upper side of the leaf.…”