Diversity and biosystematics of gall-inducing aphids (Hemiptera: Aphididae) and their galls in the Himalaya

Abstract

Aphids (Hemiptera) are one of the important groups that induce galls on plants. A review of the gall-inducing aphids and aphid-induced galls in the Himalaya has been made. Altogether, 76 aphid species belonging to the subfamilies Aphidinae, Drepanosiphinae, Eriosomatinae, and Hormaphidinae induce galls both of cataplasmic and prosoplasmic nature on different plant species in the Himalaya. Gall-inducing aphids mostly occur in the Western and Northwestern Himalaya and 33 species are endemic to the Himalaya. Although the specific gall-inducing generation and the galls on the primary host do not occur in the Eastern Himalaya, some aphids that are capable to induce galls elsewhere occur on secondary host plants in that area. Various types of galls on leaves and stems occur. Generally gall-inducing aphids and their host plants are species specific. A few host plants, for examples, Populus ciliata, Prunus cornuta, Pistacia integerrima, Ulmus spp. harbor more than one gall-inducing aphid.

Although gall-inducing aphids are mostly holocyclic and heteroecious, a few species such as Hamamelistes miyabei, Hayhurstia atriplicis, Pemphigus siphunculatus, Pterocallis afflnis, Thecabius qffinis, Tinocalloides montanus, are autoecious. Two-year cycle has been observed in some species of Fordini. Resource partitioning among species occurring on the same host plant has also been observed. A few pemphigine species have soldier morphs involved in either gall defense or territorial fighting for selection of gall-site and protecting galls from the invasion of other clones and cleaning the galls.

Trophic relationship of aphids and their galls shows that throughout the growth period aphids obtain a steady supply of nutrients. Accumulation of phenolic compounds above a threshold level plays an important role in the immigration of aphids from the galls. Natural enemies associated with gall-inducing aphids are few and that on prosoplasmic galls induced by the species of Baizongia, Epipemphigus, Forda, Kaltenbachiella, Pemphigus, Tetraneura, are limited. Out of the 24 hymenopteran parasitoids known, 9 species are endemic in the Himalaya. In comparison, all predators are non-specific and none is endemic. Predators include cocconellids (13 species), neuropterans (6 species), anthocorieds (7 species), and syrphids (5 species). Biological studies on these natural enemies have also been reviewed.

Key words:

• Gall aphids
• aphid galls
• Himalaya
• taxonomy
• biology
• distribution
• trophic relationships