A grasshopper and its beneficial drug source: The African story of Zonocerus variegatus and the neophyte Chromolaena odorata

Abstract

Since the 1970s, the pestilence of dry season populations of the polyphagous grasshopper Zonocerus variegatus (Orthoptera: Pyrgomorphidae) has impacted negatively on agriculture and forestry in Sub-Saharan Africa. Current chemoecological knowledge indicates that outbreaks of Z. variegatus may be due to sequestration of protective Pyrrolizidine Alkaloids (PAs) from the introduced perennial shrub, Chromolaena odorata (Asteraceae; Eupatorieae). Abetter knowledge of the impact of the plant PA system on the performance of Z, variegatus should help to develop efficient strategies for controlling outbreaks of Z, variegatus. The influence of the accessibility of a PA source (dried roots of C. odorata) on the development of Z. variegatus reared on cassava foliage as sole nutrient source was studied. The comparative studies, in which females and males were analyzed in separate trials, revealed that in the presence of the PA source Z. variegatus showed: (1) A slightly higher survival rate, (2) Significantly increased body weight and size (increased length of the thorax shield) and (3) Females produced heavier egg pods with more but lighter eggs. Eggs produced in the presence of the accessible PA source were found to contain PAs in concentrations known to efficiently protect eggs of PA sequestering Lepidoptera (e.g., arctiid moths) against various predators and parasitoids. Participation of a female-to-male-transfer of PAs could be excluded. The results suggest that in Z. variegatus, as in PA adapted leaf beetles and Lepidoptera, the acquisition of the plant PA system and its integration into the insect's biology is associated with specific functional and behavioral adaptations.