Insect stowaways

From animals moving by their own agency, let’s consider the other side of the coin, when us humans get involved in moving animals around. Invasive species - foreign species introduced by humans to a new habitat - are a major concern for maintaining the diversity of species on the globe, and whereas some cases of introductions are purposeful, many are accidental. Australia is well known for its unique wildlife, and much effort goes into protecting it with various measures to prevent and deal with invasive species to minimise the impact on native animals and plants, and subsequent impacts on society. This is known as biosecurity, and expert Simon McKirdy at Murdoch University in Perth, Western Australia, has recently analysed a 1,500 cabin cruise ship for stowaway insect life, to better understand the biosecurity risks posed by these global transport links to vulnerable habitats...

Simon - We've been heavily engaged in working with an island that has one of the world's largest natural gas plants on it. And when this project commenced, there was requirements put on by both our federal and state government, that the developers were not allowed to introduce a single what was referred to as a non-indigenous spaces or an invasive species to the island. The island was actually very much as it was pre the separation of this island from the mainland. So for more than 8,000 years, what's been living on that island was quite unique. And for some species that have become extinct on the mainland, this is their only last reserve. And so because of that, there's been very strict requirements put in place as to how that island would be protected.

In developing up a gas plant on the island, a decision was made to bring a cruise vessel, 1500 cabin size, bring it to the island to operate as an accommodation facility for more than 15 months. And because that vessel was operated for most of its working life in the Baltic, we then set up detailed surveillance on that vessel to find out what organisms were actually living on that vessel and what organisms might pose a risk to the island when the vessel arrived. We identified a number of insect species on the vessel that posed a significant risk not only to the Island, but also to Australia as a whole.

Katie - How do you go about surveying and monitoring that enormous boat?

Simon - We actually set up quite an extensive programme. We had scientists on board the vessel every day for that 19 months, extensive maps of the vessel. For the first period it was very much about looking over every part of the vessel in quite an intensive way. Part of that also included actually, you know, lifting carpet, dismantling wooden seating and things to try and get into any of the little holes and nooks where insects might live. And then through a process of starting to map where the insects were at a broad scale on decks, then to focus our efforts in on the particular decks where there was significant populations. So the insects that we were particularly concerned about, which were insects that are normally a concern with stored products, they were all around the decks where there had been bars in the previous life of the vessel - restaurants, dining rooms, nightclubs. So anywhere where people were consuming a lot of food or drink, that's where the insects would be. And our theory in the end on why we continued to find so many insects in those areas was just that when humans are there eating and drinking, we just naturally drop a lot of food and drink. And so it's the mix of, you know, the human detritus skin and that, that we just drop every day, food crumbs and spilt drinks that had become this long-term food source to keep these insects alive.

Katie - Were there any insects that were particularly successful stowaways?

Simon - Yeah, there was one in particular and it was the one that we actually considered was the biggest threat to Australia. And that was an insect called tribolium destructor, a tiny little beetle, we're only talking, you know, a beetle of about five millimetres in length. But despite all the effort we put into hunting for this beetle and baiting and trapping and chemical treatments, even at the end of the 19 months when that vessel sailed away, we had not managed to kill the population. We were still finding larvae on the last few days before it left. You know, we didn't eradicate the insect from the vessel, but what we did manage, and that was also an important part was, we didn't want the beetle to leave the vessel. If it left the vessel and then got introduced to the island and then to Australia, you know, that could have been a significant threat. So we set up a strong biosecurity system on the vessel where every single passenger that left the vessel had their luggage inspected. And we also did a lot of communication with the people that lived on the vessel, which were workers on the island, in communicating to them the importance of making sure they weren't carrying any of these insects as hitchhikers. And to make sure, you know, their luggage was clean when they left. And through that process, we were successful in making sure that the insect did not leave the vessel.

Katie - How would you summarise the significance of this work? Because it sounds like there aren't just lessons here to learn for Australia. Cruise liners go, well by definition, all over the world.

Simon - Yeah. Covid has thrown up an interesting discussion around cruise vessels and what they'll look like for the next, you know, few years. But what we had seen up to before Covid arrived was quite a rapidly increasing industry. And there was this need with passengers to keep visiting more and more remote locations. To us, the biggest message out of this - and from a biosecurity perspective, the concern - is that if we are going to allow cruise vessels to visit remote and vulnerable locations where we have very few or no invasive spaces, then we have to be very conscious of the risk that they may introduce pests into these areas. I don't think we should assume that just because from a surface view a cruise vessel looks very clean, it is possible that, you know, lurking underneath cleanliness layer is a population of insects that could pose a significant risk to a new area.