Native insect jumps to eggplant
From the February 2009 edition of Agriculture Today.
Gosford Horticultural Institute scientists are intrigued by a sap-sucking insect which appears to have jumped from its usual host species and begun attacking eggplants.
The insect is a psyllid, a sapsucking insect like an aphid which is commonly seen on wattle and eucalypt trees.
"In Australia psyllids have not been known to infest or attack vegetable crops - until now," NSW Department of Primary Industries entomologist, Dr Deborah Kent, said.
"In 2007 an as yet undetermined psyllid species belonging to the genus Acizzia was found feeding on eggplants in the Sydney Basin.
"The usual host plants of this psyllid genus are wattles."
So why has this psyllid switched to feed on eggplant?
"We are not sure, but a number of insect species are capable of having multiple hosts of completely different plant types at different times of the year," Dr Kent said.
She said the Acizzia psyllid had been found two years running in a western Sydney backyard vegetable garden.
On each occasion the psyllids were only noticed in late summer and early autumn.
The variety of eggplant affected in 2007 was a Long Tom variety, while in 2008 both Long Tom and more traditional Black Beauty varieties were affected.
The same psyllid species had been previously reported from the Central Coast, as early as 2005, again on eggplant and again in a backyard garden," Dr Kent said.
"Eggs are laid directly onto the underside of the leaf surface and are attached by a thin stalk.
"The newly emerged nymphs are clear to white in colour with numerous spiky hairs and, unlike young aphids, are relatively flat in shape.
"Both adults and nymphs are found on leaves mainly on the under surface of the leaves or near new growing tips."
Dr Kent said that at this stage the only solanaceous vegetable infested in the Sydney Basin was the eggplant Solanum melongena.
Tomatoes and capsicums that have been exposed to the psyllids both in a garden situation and in a laboratory greenhouse have not become infested.
Damage to the eggplant seems to be confined to the new leaves at the growing tips and flowers.
Severe feeding damage has caused the death of growing tips and the premature loss of flowers.
This psyllid has a unique method of disposing of excess plant sap known as honeydew.
Both the adults and the nymphs package the honeydew within a plastic-like sac which can be seen as silvery globules or threads adhering to the leaves.
A small parasitic wasp was found parasitizing large nymphs late in the 2007 season and this supports the belief that the psyllid is a native species rather than an exotic.
"A single survey of a commercial eggplant grower in the western Sydney Basin during spring 2007 found no psyllids," Dr Kent said.
"However, in March 2008 a single psyllid was collected from a commercial eggplant crop in the Freeman’s Reach area by DPI staff from Gosford and Richmond.
"This agrees with the observations in the suburban backyard and it is possible that commercial growers may only be affected late in the season."
Due to its similarity to aphids the psyillid may well be overlooked in general monitoring.
"I am interested to hear from any grower, commercial or backyard, who has noticed this insect either on eggplant or another solanaceous crop such as tomato, capsicum or potato," Dr Kent said.
Contact Deborah Kent, West Pennant Hills, (02) 9872 0133.
