The lesser of two weevils: Investigating bug diversity and distribution at a coastal wetland restoration site

By Tallulah Davey | News, Fieldwork, Labwork | Comments are Closed | 25 June, 2024 | 14

A unique opportunity to explore bug diversity

Avalon Coastal Complex – just north of Geelong, Victoria – was historically full of thriving coastal wetlands, with vast saltmarshes, natural mudflats and seagrass meadows just offshore. However, many of these coastal ecosystems were lost due to the construction of a large-scale salt works, when much of the site was landscaped into a network of salt ponds. With salt production long ceased, the area has become a perfect candidate for restoring degraded wetlands back to their former glory.

One of the key ecosystem services that coastal wetlands provide is habitat to support biodiversity. When we think of coastal wetlands, often larger animals like shorebirds, fish, frogs, and reptiles spring to mind. An often-overlooked component of bustling wetland biodiversity is that they are teeming with invertebrates, aka ‘bugs’. Coastal wetlands support a huge variety of macro-invertebrates (i.e. bugs you can see), though little is known about the communities of bugs across these coastal wetlands, and how they may change as we restore degraded areas.

Sweeps, beats and mud samples make for a successful catch

Our scientists recently undertook baseline surveys across the vast wetlands at Avalon Coastal Complex to inform our understanding of the biodiversity prior to restoration, collecting swathes of data, including a lot of bugs. Researchers collected the bugs using four different methods, to capture as much diversity as possible:

Sweep nets, for flying and hopping bugs
Bush beating, to sample bugs living in foliage and on vegetation
Direct collection, for bugs moving around on the ground
Soil cores (or as we like to call them, mudcakes), to give us a snapshot of all the bugs living within the soil

Left: Sorting through and collecting specimens after a sweep net in saltmarsh habitat. Right: a freshly collected macroinvertebrate soil core (“mudcake”) sample.

We collected over 2,500 bugs across the saltmarsh, seagrass, mudflat, subtidal sand and salt pond ecosystems. After hours of dedication looking under the microscope, specimens were identified to the lowest possible taxonomic level. Our next step will compare how the species differ between the diverse sites and ecosystems e.g. salt ponds versus established saltmarshes. Our upcoming winter surveys will contribute to this, so that we have a great overview of bug diversity that we can compare across seasons as well as after we have restored coastal wetlands in the area.

Check out some of the bugs we uncovered and the key roles they play within the ecosystem:

Dive into the world of weevils

Allow us to introduce our two favourite weevils:

The first is a Fungus Weevil (Xynotropis micans), which spends its time eating fungi and decaying plant matter, providing a critical role in the ecosystem by contributing to decomposition and nutrient cycles. This individual was found through bush beating the vegetation in healthy saltmarsh next to a lagoon.

Our second weevil may look friendly, however this White-fringed Weevil (Naupactus leucoloma) is in fact invasive in Australia! Native to South America, all individuals outside its native range are female and reproduce through parthenogenesis (i.e. asexual reproduction, where embryos grow without the need for fertilization). Larvae of this species are known to feed upon the roots of at least 385 different plant species, and adults feed on their leaves. They are most commonly found in pastures and can cause menacing damage to crops. This individual was found in a salt pond, where she was likely searching for a good place to lay some eggs, as adults are generally only active for up to three months over the summer.

Agile arachnids

Avalon Coastal Complex is also blessed with a high abundance and diversity of arachnids, both mites and spiders. Some of the most visually striking are jumping spiders from the genus Simaethula, whose metallic gold colouration makes them a perfect subject for microscope photography.

Jumping spiders have some of the best eyesight among arthropods, and as their name suggests are agile jumpers. Just before a jumping spider makes a jump, it tethers a ‘dragline’ of silk to whatever it is standing on, which provides a mechanical aid for purposes of braking and stabilisation while also acting as a failsafe if the jump were to be unsuccessful. So, they are really more like bungee jumping spiders! They are effective predators and use their excellent vision and precision jumping to capture and poison all kinds of prey.

Other kinds of spiders found in abundance at Avalon include Wolf spiders (Artoriopsis expolita), Lynx spiders (Oxopes sp.) and Orb weavers (Socca sp.). Some less common spiders found were Red and Black spiders (family Nicodamidae), Crab spiders (Sidymella sp.) and Stretch spiders (Tetragnatha sp.) among many others.

Connecting the dots

Returning to our six-legged specimens, we found particularly high numbers of lady beetles. Several species were observed with the most dominant being the Variegated Lady Beetle (Hippodamia variegata). This species was introduced to Australia around the year 2000, and is actually seen as beneficial in crop bio-control, helping to control the numbers of pests that damage growing crops.

Also present but in smaller numbers were the introduced Eleven-spotted Ladybird (Coccinella undecimpunctata), the native Striped Ladybird (Micraspis frenata) and Large Spotted Ladybird (Harmonia conformis). We also found two Black Ladybird specimens (Rhyzobius forestieri) that are native to Australia. Interestingly, this species was introduced to Europe in the 1980s as a bio-control agent.

Glittering beetles

A particularly striking beetle we collected was the more straightforwardly-named Red and Blue Beetle (Dicranolaius bellulus). This species is endemic to Australia and plays an important role in coastal wetland ecosystems. Often regarded as pests to the agriculture industry, they are predators of many insects, eating a variety of larvae and eggs as well as pollen. Much like our field researchers (who were out collecting specimens in 35+ degrees!), these beetles are heat-tolerant, able to control prey populations when other predators like lacewings die out from the intense Australian summer heat.

The truth about true bugs

So far, we have been using the very general term ‘bug,’ so it would be remiss not to discuss True Bugs, those of the order Hemiptera. In many entomologists’ opinion, these are the only organisms that should be called bugs. At Avalon Coastal Complex we had a smorgasbord of true bugs, including the ambush predators the Assassin bug (Coranus sp.) and Brown Soldier Bug (Cermatulus nasalis), which use their long proboscis to inject a lethal saliva that liquifies the insides of their prey. There are also False Chinch Bugs (Nysius sp.), and Dictyopharid Planthoppers (Thanatodictya sp.) who predominantly feed on plant sap.

Keep your antennae tuned for more

These bugs barely scratch the surface of the diversity of the specimens we collected, and we are hard at work distilling our results. So for now, enjoy a few more jumping spider highlights from the microscope camera and stay tuned for many more bug updates to come!