Natural history of Cassida sphaerula Boheman, 1854 (Coleoptera: Chrysomelidae: Cassidinae: Cassidini) on Arctotheca prostrata (Salisb.) Britten (Asteraceae: Arctotidinae) in South Africa, with a checklist of South African Cassidinae (leaf-mining and tortoise beetles)

Abstract

The tortoise beetle, Cassida sphaerula Boheman, 1854 (Coleoptera: Chrysomelidae: Cassidinae: Cassidini) is endemic to South Africa. Its endemic host, Arctotheca prostrata (Salisb.) Britten (Asteraceae) has been introduced in other countries where it is becoming invasive. Cassida sphaerula could provide a potential biocontrol of Arctotheca weeds as it spends the entire life cycle on this host. An intensive field study, with rearing, photography, and short films of C. sphaerula was conducted in its native habitat to document the life cycle. A checklist of Cassidinae genera in South Africa, along with 19 new host records for Cassidini species in South Africa are presented. Oothecae are simple, with few laminate membranes enclosing fewer than five eggs. There are five larval instars. Larvae and adults feed by making a series of cuts in the ventral cuticle, forming an arc, and they consume the mesophyll as the cuticle is rolled to one side. This creates many ventral craters, thickened on one margin with the rolled cuticle; these ventral craters correspond to ‘windows’ in the dorsal leaf surface where the dorsal cuticle is left intact. This unusual feeding pattern is known in three Cas¬sida species, all in South Africa. Like many tortoise beetles, instar I initiates a feces-only shield on its paired caudal processes (= urogomophi); this construction is retained, along with exuviae, by subsequent instars. The shield construction was studied by film and dissections. This revealed that the columnar or pyramidal shield in this species has an exterior of dry or moist feces that obscures the central nested stack of exuviae, each exuviae compressed onto the caudal processes. Pupae may retain the entire larval shield of exuviae and feces or only the 5th instar exuviae; this behavioral flexibility in pupal shield retention is novel for tortoise beetles. Behaviors of C. sphaerula are discussed in the context of phylogenetic characters that can give evolu¬tionary insights into the genus, tribe, and subfamily.

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