Ask yourself this question. Do you like moths? If one was to swoop into your periphery at this very second would you be curious, ambivalent, or terrified? I am willing to bet that many of you reading this will have a particularly strong opinion of our scaly-winged compadres. I am a card-carrying member of the Pro-Moth faction when I’m not fan-girling over a cool mushroom (plant pathology student here!). Perhaps I can change your view of these incredible creatures.
- Moths love to party ( watching a moth flutter around a light source is very reminiscent of a disco fan gyrating under a strobe light on a Saturday night).
- Moths have a face only a mother could love ( which is in and of itself, its own brand of cuteness)
- Moths are the subject of many great memes
Whether you love or hate them, there is no denying that in every group, there are always a few bad eggs. One moth species, in particular, is a VERY BAD EGG.
The diamondback moth (Plutella xylostella) has caused quite a furore in the last few years because of mass-feeding damage on brassica species. Management strategies cost an estimated value of US$ 4-5 billion worldwide. Diamondback moths are voracious critters that are attracted to a mixture of popular vegetables, such as cabbage and broccoli, whilst also feeding on forage brassicas, such as kale and canola. It is the caterpillars of this moth that do the damage. Early instars eat by leaf-mining, and, when the caterpillars are more developed, they begin to burrow completely through the leaves.
Previous population control strategies used an over-reliance of broad-spectrum insecticides. The future of control is uncertain due to increased incidences of resistance in many populations. Sustained use of insecticides may also have negative impacts on non-target fauna, as well as other environmental and health risks. In New Zealand, two parasitic wasps (Diadegma semiclausum and Diadromus collaris) have been utilized as biological control agents for these moths; however, the efficacy of these agents, whilst promising in the North Island, has been shown to be lacklustre in the South Island.
Another control option is currently being explored, and that is the use of endophytic entomopathogenic fungi. There is a myriad of advantages that stem from the potential use of an endophyte (a fungus that lives inside plants) that can control diamondback moths. Advantages include general cost-effectiveness, a decrease in chemical residues introduced into the environment, and the potential to promote plant defenses and growth.
Personally, the mental image evoked when imaging a fungus slowly invading and diminishing the life of a hapless moth, provokes the same sick curiosity that one may feel upon seeing a dead pigeon sprawled outside the entrance to the Burns building. It is morbid, to be sure, but you just can’t help but look.
In a study undertaken to find appropriate fungi to use as potential biocontrol agents, Michal Kuchár and associates from Lincoln University, Canterbury University, and Plant & Food Research isolated 52 endophytic fungal isolates from cabbage plants. They fed leaf disks covered with spores to diamondback moth larvae obtained from a colony that has been maintained for over a decade at Lincoln University. They found that 32 of the 52 isolates induced varying rates of mortality among the larvae, with the highest rate achieved by three isolates of the fungus Lecanicillium muscarium (mortality rates greater than 80%).
Work will be done to best formulate these isolates for commercial use. Future research will need to focus on honing the optimum dosages, formulation, and manner of application in order to make it competitive with current control methods. It is not uncommon to see higher incidences of virulence in a controlled lab setting, versus in the field, and so future research should explore transferring this experiment into a natural field setting in order to fully understand whether environmental effects will alter the deadliness of fungal isolates.
Previous work has examined the use of Lecanicillium spp. as a commercial product for the control of other pests, such as whiteflies and thrips. So, there is promise! As a student currently studying plant pathology, it is my naive little hope that we shall one day remember the use of chemical controls as a not so fond distant memory. Until then, we do things like release fungi onto naughty critters and hope that by manipulating nature, we can bypass the damage done by our own past folly, and if that doesn’t work, it still makes for a hell of a good story.
P.S. While Team Moths is cool, I’m Team Fungus all the way.
Annaleze Cole is an ECOL608 student currently in her honours year of a BSc(Hons). Her favourite pastime is trying to decimate noxious weeds with fungi.