The influence of food plant quality on the fecundity of Megamelus scutellaris Berg (Hemiptera: Delphacidae), the latest biological control agent of water hyacinth, Eichhornia crassipes (Martius) Solms-Laubach (Pontederiaceae)

The influence of food plant quality on the fecundity of Megamelus scutellaris Berg (Hemiptera: Delphacidae), the latest biological control agent of water hyacinth, Eichhornia crassipes (Martius) Solms-Laubach (Pontederiaceae)
Sven Tozer, Julie A. Coetzee
Department of Zoology and Entomology, Rhodes University, Grahamstown

The quality of host plants has a direct influence on herbivore life history traits such as fecundity, body size and development. Megamelus scutellaris Berg. (Hemiptera: Delphacidae) is the latest arthropod to be released in South Africa for the biological control of water hyacinth, Eichhornia crassipes (Mart.) Solms.-Laub.  (Pontederiaceae).  Megamelus  scutellaris  expresses  two  wing  phenotypes,  a  long winged (macropterous) form, and a short winged (brachypterous) form; the production of either wing form has both beneficial and negative aspects. Each is an adaptation to maximise the availability of resources; macropters disperse to escape overcrowding and deteriorating conditions, while brachypters are mainly sedentary and attain their highest densities in the presence of high or increasing food quality. The trigger mechanism[s] initiating the production of either wing form is not well understood, but may include environmental stimuli such as host plant quality, nutrition, density, temperature and photoperiod. The aim of this study is to determine the effect of nutrition and host plant quality on the fecundity of M. scutellaris. The results of the study are important for biological control of water hyacinth in South Africa because many southern African water systems are highly eutrophic due to pollution and may affect the probability of M. scutellaris establishing in the field. The nutrient status of water bodies may therefore need to be taken into account when sites for the release of M. scutellaris are chosen.