Carolin Götze, global application and scientific coordinator, department for application technology, Getia Degesch Group.
Carolin Götze is the global application and scientific coordinator at the department for application technology at Detia Degesch Group. She is a trained biologist with a bachelor’s degree of biological sciences and a master’s degree of biology. Her postgraduate education focused on toxicology. Götze joined Detia Degesch in 2015, in regulatory affairs, and switched to application technology in 2016. Her department’s responsibilities include post-harvest efficacy trials, exposure assessments regarding residues, toxicity, and eco toxicity. Götze is also involved in external research, as well as project coordination and communication.
Tobacco Asia (TA): How is the term “phosphine resistance” to be understood? It’s not complete immunity by tobacco beetle populations against phosphine gas fumigation, is it?
Carolin Götze (CG): Thank you for addressing this very important issue. Yes, “phosphine resistance” does indeed not mean that there’s absolutely no way to fight the insects with phosphine any longer. We must be careful not to confuse tolerance with resistance. Tolerance means the direct observation of an occurrence that happens most probably after fumigation, while resistance is something that solely can be reliably investigated in a lab. So there’s kind of a difference between user versus scientific personnel understanding. Phosphine resistance is something that has been claimed over the last decades, but it is definitely not a term that should be used carelessly. For better understanding, I prefer the term “decreased susceptibility.”
TA: Okay, so “decreased susceptibility” instead of “resistance” then?
CG: Yes, absolutely. For that is what a user or an applicator sees after a potential failed treatment, and it basically covers what is being investigated in the lab, when people are looking at the behavior of the beetles of selected strains.
TA: So, phosphine gas will still work fine, but in some populations, and depending on how the applicator carries out the fumigation, there might be some decreased susceptibility in certain beetle strains. Did I understand that correctly?
CG: Exactly. It’s definitely a matter of how the treatment is being conducted. And if your first treatment fails, you should consider the option (and regulatory background) of doing another one. In that case please consider thorough sealing and monitoring as well as longer exposure times, as well as adapted dosing and conduct of tolerance testing priorly.
TA: Would it be correct to say that not all tobacco beetle populations around the world are equally displaying decreased susceptibility to phosphine gas, but that the issue is restricted to certain regions and perhaps also to certain sub-strains of tobacco beetle? In other words, how pronounced and widespread is this decreased susceptibility in reality?
CG: We lately see a higher occurrence, or a higher reporting of decreased susceptibility, in areas where we have a lot of storage facilities that, for example, handle tobacco… but not only tobacco, because this beetle is not only feeding on tobacco. Lasioderma feeds on many agricultural commodities, like grains and other cereals. And to be even more exact, it’s not the weevil [i.e. adult beetle] eating the tobacco, but its larvae which cause the damage. Populations move from one commodity to another, from one storage object to another. The species can fly. Their activity, though, is very dependent on air temperature, so you tend to find tobacco beetle in warmer regions. It cannot really survive winter times very well, so we don’t find it much in more northern regions.
TA: Okay, so the beetles cannot really survive in cold climates. But of course it can be introduced by way of a contaminated shipment, can it not?
CG: That’s correct. Due to our way of globally interacting with each other, the likelihood of (storage) pests being put into regions where they do not occur naturally because of [unfavorable] climate conditions, you can [still] have them in storage facilities where there is a pretty warm and nice environment for them.
TA: And yet, it’s rather perplexing how tobacco beetle developed decreased susceptibility in the first place. What happened from a scientific stand-point? Why do certain populations develop decreased susceptibility while others don’t?
CG: We know now that there are certain mutations within the genetics or the genome of beetles that exhibit a degree of decreased susceptibility. However, these mutations did not occur due to [exposure to] phosphine. That’s a major misunderstanding. It’s not like you expose them to phosphine and then there’s kind of a mutation and then you have less susceptibility towards phosphine. Rather, there potentially are other external influences for this occurrence than only phosphine exposure, because we also know that these [same] mutations can be found in wild range populations as well as in samples from storage facilities. So it’s nothing that you only find in treated populations. You need some kind of a trigger [to effect mutations], and this can be anything; and it’s not necessarily correlated with phosphine.
TA: In simpler terms, exposure to phosphine is not the scientifically established cause of decreased susceptibility, but it comes from other factors, right?
CG: Exactly. We have observed decreased susceptibility also during other treatment types. For example, I’ve seen some data from low oxygen treatments, where beetle strains that had been pronounced as being phosphine resistant also exhibited a lower susceptibility towards low oxygen treatment.
TA: How can that be?
CG: This is about [natural] selection processes. From [beetle] generation to generation, you can see that whenever you pressure them with sub lethal concentrations [of a pest treatment] that there can be some kind of a change. … When one generation has a low tolerance level, meaning that it shows some degree of decreased susceptibility, then the next generation might exhibit a bit more decreased susceptibility.
The less susceptible specimen reproduce, until most of this particular population exhibits this specific trait.
TA: Are we talking evolution here?
CG: Exactly. We are live observers of evolution.
TA: That is amazing! But at which development stage is the beetle actually most resistant… or to stick to the term, displays decreased susceptibility?
CG: Phosphine gas interrupts an organism’s metabolism, effectively preventing that oxygen reaches the cell mitochondria to generate ATP [adenosine tri-phosphate], the body’s energy carrier. That means that any life stage with a high metabolic rate has a higher chance of being successfully erased [with phosphine]. Tobacco beetle has 4 life stages: the egg, the larva, the pupa, and the adult. As the eggs have the lowest metabolic rate of these stages, as in near-zero, they therefore show the highest rates of decreased susceptibility [to phosphine].
TA: Let’s cut to the chase. Is phosphine fumigation still effective? And what should be done by storage facility operators and manufacturers to keep the incidence of decreased susceptibility as low as possible?
CG: The actual key term here is “IPM,” so “integrated pest management” strategies. We do have a lot more than phosphine gas to prevent and also fight infestations. One key aspect is definitely preventing infestations in the first place. The storage facilities themselves… are they suitable to even store tobacco? Sanitation and hygiene measures also matter a lot. Then, of course, you can play with temperature. You can disrupt opportunities for the beetle to thrive. You also have low oxygen treatments. So, there really is a lot of actions to be considered before starting a phosphine fumigation as a last resort. It definitely shall be seen as a last resort, and not as the only and all-time weapon suitable for any kind of object and location and situation.
I’d actually like to quote a colleague of mine from the US who said that phosphine is actually the only insecticide that can break its own resistance. This is a unique trait and impossible to be achieved with any other kind of insecticide. So, if you carry out the fumigation properly and according to protocol, you will be successful. However, there’s still a lot that you have to keep in mind and follow through with, not only during fumigation but also post-fumigation. Phosphine won’t linger and have a long-lasting protective effect. Rather, it’s something that works now and immediately.
TA: So in the end, affected manufacturers or warehouse operators, they needn’t panic in case of an infestation, right?
CG: That’s correct. Operators should keep their eyes open when storing tobacco and moving it around. Insects such as tobacco beetle can be very mobile. They can occur at any point in the logistics chain. Operators shouldn’t feel helpless or intimidated by all the research that’s being done on the subject of resistance or decreased susceptibility and be concerned that we don’t have any weapons against insects any longer.
TA: And companies like Detia Degesch can of course offer assistance whenever there are questions regarding an infestation or how to get rid of it, correct?
CG: Of course. If you need advice or help or support regarding any kind of infestation, insect infestations in particular, then please be in touch with us. Our website address is dd-group.com. You will find various contact tools there.