Plant Doctor Archive

Bug alert

WHAT are these eggs and insects on the undersides of my canna leaf? I've also seen them on grapes. Are they green beetles?

THEY look like the eggs and young (nymphs) of the green vegetable bug which some gardeners call shield beetles or shield bugs.

The nymphs change colour as they develop from orange to shiny black and eventually to the green of the mature adult, though there is a relatively rare variety which is orange at maturity. They feed by stabbing their sharp hypodermic-like mouthparts into soft plant tissue and suck the sap.

You generally find them in warm sunny spots in the garden. They'll drop to the ground or fly away if disturbed. It's not uncommon in a late summer evening for them to be attracted to bright lights and come indoors where they can blindly fly around. They exude a foul-smelling liquid if provoked, hence their other common name of "stink bugs".

They can be a major pest of susceptible plants like tomatoes, beans and passionfruit, causing deformed growth, lack of vigour and poor fruiting, but are seldom a problem among ornamentals. Most common broad spectrum insecticides can be used to control them if necessary.

Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.