What are the ants doing in the tree?
As winter sets in there are less and less flying insects to be seen, which might seem like a bad time to be an entomologist. But even in the middle of June there are still plenty of insects around – you just need to know where to look. Personally when I get a bit desperate for hexapodal company I head for the nearest gum tree.
Gum trees (Eucalytpus spp., Corymbia spp and Angophora spp.) are hosts to myriad insects but today I want to talk about the insects which form “lerps” on gum tree leaves. A lerp is the white sugary, waxy covering which the immature stages of some psyllid insects (family Psyllidae) produce from liquid excretions known as honeydew. There is disagreement among scientists as to the purpose of the lerp. Some argue that the lerp is protection from predators, while others insist that it provides the immature psyllid with a more humid environment. Perhaps it is a mixture of both. The image below shows an intact lerp in the upper image and then moved to reveal the Glycaspis sp. nymph underneath.
Have you noticed swollen bronze-coloured aphids on your plants? These are aphid ‘mummies’ caused by the parasitic wasp Aphidius of the wasp family Braconidae. There are several species of Aphidius which have been released in Australia. A species that has established well and is common in urban gardens is Aphidius rosae, a successful parasite of the rose aphid Macrosiphum rosae.
Aphidius wasps are shiny black, slender insects about 3 mm in length with long antennae. The diminutive size of these wasps makes it hard to see them in gardens, but you will see the results of their life cycle within aphids. Adult female wasps lay their eggs singly inside adult aphids and aphid nymphs. To accomplish this a female wasp must bend her abdomen under her legs and inject an egg into the aphid with her ovipositor (‘stinger’). If you were watching and you blinked, you would miss it, as this operation takes less than a second. Obviously I don’t have many images like this one.
Night of the Bloodsuckers (Part 1) prompted several conversations, and people had lots of suggestions about how to control or repel mosquitoes. The repellent suggestions included lemongrass, citronella, and garlic oil spray (a product not available in Australia as far as I know). In addition to emptying pot trays, bird baths etc regularly to stop mosquitoes breeding, one correspondent reminded us not to forget emptying bromeliads. One ingenious person suggested deliberately placing buckets of water around the garden to encourage mosquitoes to lay their eggs in them, and then emptying them out. That’s using buckets as a trap! Thanks for all your suggestions.