Slugs and snails are the bane of just about each vegetable planting gardener and farmer. Slugs specifically have voracious appetites and are relentless in consuming stems, leaves and shoots. No marvel gardeners have sought any means to manage the unfold of this crop killer. Sadly, the most typical response – slug pellets – can have a horrible impact on different wildlife. One various is the parasite Phasmarhabditis hermaphrodita, a nematode worm which naturally kills slugs and snails.
Till just lately, we had little thought why this parasite was so efficient. Our current analysis, revealed in Behavioural Processes, reveals that after P. hermaphrodita infects the slug, it takes management over its behaviour, basically remodeling it right into a zombie. By delving additional into how this parasite takes management of the slug’s behaviour, we are able to achieve a greater understanding into the molecular intricacies of thoughts management and even the best way to management the behaviour of slugs en masse.
Slugs are notably very onerous to manage as a result of they will transfer deep into the soil and produce an incredible variety of offspring. Management strategies which have tended to deal with slug pellets may be washed away simply and are extremely poisonous to a variety of different wildlife. For many years, these pellets have contained methiocarb and metaldehyde, each of which may be dangerous to the surroundings. Methiocarb has now been banned and the usage of metaldehyde round waterways is below strict regulated use.
The P. hermaphrodita parasite then again is an natural and efficient various for controlling slugs. When added to the soil the parasites will hunt, infect and kill any slugs they discover inside 21 days. Then the nematodes reproduce on the cadaver and go in quest of any slugs that beforehand escaped them. There are 108 species of nematodes that infect slugs and snails. However in contrast to others, P. hermaphrodita is extremely particular and doesn’t have an effect on different invertebrates comparable to bugs or earthworms.
Peter Andrus, CC BY-SA
Our analysis additionally confirmed that the nematode worm P. hermaphrodita has the exceptional potential to manage the behaviour of slugs. Ordinarily, when within the presence of parasitic worms, slugs sense hazard and slither away in concern of being fatally contaminated. However when slugs are already contaminated, they appear to be drawn to areas the place the parasite is current and can fortunately stay in an space the place they danger additional an infection.
By directing the slugs in direction of extra parasites, P. hermaphrodita lead the slugs to their dying, after which the nematodes can feast on the carcass and reproduce. We had beforehand proven that a number of slug species averted P. hermaphrodita however have been very shocked to see that a number of different species, when contaminated, have been drawn to the nematodes. This behaviour was induced particularly by P. hermaphrodita however not different nematodes.
Its all within the serotonin
To know precisely how these nematodes have been controlling the slug’s behaviour, we started a drug-based experiment, wherein we fed uninfected slugs the antidepressant fluoxetine (Prozac). Fluoxetine will increase the extent of serotonin, the chemical sign or “neurotransmitter” that regulates temper in lots of animals. Amazingly, these drugged slugs have been drawn to the nematode-infested soil in the identical manner as slugs contaminated by the parasite.
We additionally discovered that nematode-infected slugs fed cyproheptadine, a drug which does the other of prozac and blocks serotonin, have been not drawn to the nematodes. All of this implies P. hermaphrodita manipulates serotonin signalling within the slug’s mind to alter its behaviour.
P. hermaphrodita isn’t alone on this behaviour and lots of parasites have developed to manage the thoughts and behavior of their hosts. Protozoa comparable to Toxoplasma gondii make contaminated rats lose their concern of cats. A fungus referred to as Ophiocordyceps spp. takes over ants and causes them to climb up bushes so the fungus can higher disperse its spores. Trematode flatworms
are masters of manipulation, with the power to manage the behaviour of quite a lot of organisms.
Whereas the proof helps the concept that P. hermaphrodita controls its hosts by affecting neurotransmitters comparable to serotonin, T. gondii interferes with manufacturing of one other neurotransmitter, dopamine, to alter the behaviour of rats. We additionally know that injecting serotonin into crustacean brains can mimic the behavioural modifications attributable to acanthocephalan worm parasites. And the parasite Euhaplorchis, alters the stability of a killifish’s serotonin and dopamine, inflicting it to conspicuously entice the eye of feeding birds. Solely by reaching the fowl’s intestine can the parasite lay its eggs.
Our outcomes recommend that by altering the degrees of serotonin in wholesome slugs, we are able to replicate the behavioural modifications attributable to P. hermaphrodita an infection. Equally, we are able to additionally reverse the behavioural modifications of contaminated slugs to imitate uninfected members of their species.
Additional investigation may result in a greater perception into the molecular intricacies of thoughts management of not simply these nematodes however different parasites too. In the end, we may use this information to affect and direct the behaviour of contaminated slugs. We may make them transfer en masse to areas of our selecting by manipulating their serotonin ranges, and in so doing eradicate their menace and urge for food.
Robbie Rae receives funding from BASF Agricultural Specialities Restricted, which manufactures parasite-based slug management merchandise.
Sally Williamson doesn’t work for, seek the advice of, personal shares in or obtain funding from any firm or group that might profit from this text, and has disclosed no related affiliations past their educational appointment.