Solanum mauritianum Scop. (bugweed, woolly nightshade; Solanaceae), a small perennial tree from South America, is a major environmental weed in South Africa and elsewhere in the world (see review by Olckers 2011). Bugweed populations persist in a variety of habitats in South Africa, ranging from sunny, exposed habitats (e.g. grasslands, savanna and roadsides) to partially shaded and fully shaded habitats (e.g. forest/plantation margins and understoreys, respectively). The lace bug Gargaphia decoris Drake (Hemiptera: Tingidae) was released in South Africa in 1999, and later in New Zealand in 2010, for the biological control of S. mauritianum (Olckers 2000, 2011; Olckers & Borea 2009). As is typical of lace bugs (e.g. Buntin et al. 1996), high levels of sap-sucking by the adults and nymphs can reduce the plant's growth rate as a result of leaf chlorosis, reduced rates of photosynthesis and transpiration, as well as premature leaf abscission.
Specialist herbivores have evolved adaptations to overcome plant defensive chemicals and thus prefer younger leaves with their higher nutritional value, whereas generalist herbivores are unable to overcome these chemical defences, and opt for older leaves which have fewer nutrients, but are less defended (Center & Wright 1990). Plants such as the invasive aquatic weed Eichhornia crassipes (Martius) Solms-Laubach (Pontederiaceae) (water hyacinth) continuously produce young, unfurling leaves that require high concentrations of digestibility-reducing chemicals in their tissues to ensure protection against herbivory (Center & Wright 1990). These defensive chemicals are products of secondary metabolism (Berenbaum 1995) and ensure that young leaves are typically unpalatable to herbivores and resistant to disease (Center & Wright 1990).
Banded fruit weevil, Phlyctinus callosus Schönherr (Coleoptera: Curculionidae), is indigenous to South Africa, and is a polyphagous species occurring or feeding on a wide variety of weeds, grasses and ornamental plants (Barnes 1987). The oldest specimen in South African collections was collected on Devil's Peak, Cape Town, in 1884, and is housed in the SAMC: Iziko South African Museum (Cape Town), under the catalogue number SAM-COLA045063 (S. Van Noort, pers. comm.). Phlyctinus callosus is adapted to hot, dry summers and wet winters (Annecke & Moran 1982), and with one exception (the annotation of which is dubious) has only been recorded in South Africa below latitude 33°S (Barnes 1987).