Molecular structure of spinosad

Spinosyns are a group of complex chemical compounds produced through fermentation of the soil fungi Saccharopolyspora spinosa and S. pogona.

The first isolated and identified representative of this chemical class was spinosad. It was discovered in the 1990's in the laboratories of Eli Lilly.

In the meantime several dozens natural spinosyns have been identified, and several hundreds semi-synthetic derivatives have been produced in the laboratory.

Spinosyns are one of the newest and last chemical classes of insecticides discovered, in the meantime already more than 20 years ago.

Mode of action and characteristics of the spinosyns

Spinosad and derivatives are broad-spectrum insecticides and acaricides that act by contact or ingestion by the parasite, and have also a systemic mode of action on mammals. Efficacy has been shown against important veterinary parasites such as fleas, horn flies, houseflies, lice, ticks, blowflies, poultry mites, etc. But availability of commercial products with spinosyns is modest in many countries.

The molecular mechanism of action of spinosyns has not been completely elucidated. They act on both GABA and nicotinic receptors of the membranes of nerve cells of insects, but they target different subunits than other known insecticides. The good news is that spinosyns don't have cross-resistance with other currently available chemical classes of insecticides.>

Active ingredients

The most relevant spinosyns for veterinary use so far are:

Delivery forms of spinosyns

For use in livestock spinosad is available mainly in the form of pour-ons and liquid formulations for spraying and jetting or dipping of sheep. So far commercial products have been introduced only in the major markets (e.g. Australia, New Zealand, USA, a few EU countries).

There are also spinosad products for spraying poultry against mites. This is particularly interesting to control resistant red poultry mites (Dermanyssus gallinae) that have become a serious probem worldwide. Hopefully products with spinosyns will be soon available in many other places, since they are an excellent option for the control of parasites with serious resistance problems such as horn flies.

A significance benefit of such products for dairy and layers is also that there is no need to discard milk or eggs.

For use in dogs and cats spinosyns are available in some countries mainly as tablets for oral administration, alone or in combination with other active ingredients.

Safety of spinosyns

Spinosadis quite safe for mammals, birds, fish and wild animals in general. The poisoning risks for livestock and pets, as well as for operators and pet owners seems very low, also considering that it is quickly metabolized and excreted. Spinosad is also not too persistent in the environment because it is photodegradable, easily broken down in soil and water and by aerobic microorganisms, and does not bio-accumulate.

General information on the safety of veterinary antiparasitics is available in specific articles in this site (click to visit):


Never use livestock, horse or poultry products on dogs and/or cats, unless explicitly approved for dogs and/or cats too. Without reliable use instructions they can be easily overdosed, and pets may not tolerate formulations developed for use on livestock, horses and/or poultry.  Some active ingredients may be toxic to particular animals.

Never use agricultural or hygiene products on livestock, horses, poultry or pets, unless explicitly approved for veterinary use, which is quite unusual. Even if the specific active ingredient is approved for some veterinary use. The formulations for agricultural and/or hygiene use are mostly different than those for veterinary use and  may be toxic to or not be tolerated by animals.

It is obvious that veterinary medicines are not intended for and should never be used on humans!!!

Resistance of parasites to spinosyns

So far there are no reports on confirmed field resistance of veterinary parasites to spinosad. This is not surprising since spinosad products have been introduced recently.

However, there are already reports on spinosad resistance in field strains of a few agricultural pests. In addition, in laboratory tests it was possible to select a housefly (Musca domestica) pupulation resistant to spinosad after only 10 generations. It showed a resistance factor of >150.

This is a clear warning. The experience of the previous decades strongly suggets that several veterinary parasites will develop resistance to whatever parasiticide if they are put under high and persistent selective pressure. And they will develop it rather sooner than later. Among the veterinary parasites especially at risk of quickly developing resistance are sheep lice, red poultry mites, blowfly strikehouseflies and horn flies. Therefore it is crucial to use spinosyns following strategies that delay resistance development, e.g. alternating their use with products containing active ingredients with a different mode of action before resistance or even tolerance to spinosyns has developed.

Visit also the articles in this site about parasite resistance to antiparasitics and  how it develops.