Professional Pest Controller issue 93

18 December 2018

Formulation focus for gel bait performance

Advertising | PPC93 December 2018

While overall results are extremely good, understanding how different formulations work can help select the most appropriate products and help to get the best from them, reports Syngenta Technical Manager, Dr Kai Sievert.

This approach has a risk of stopping ants feeding on gel baits for several days

Our research suggests gel baits are now utilised by pest management professionals in over 80% of cockroach infestations, and around 70% of call outs to tackle ant control issues.
I would like to highlight that the protein-based formulation of cockroach gels is inherently more stable and easier to handle, compared to syrup-based ant gel baits.
The problem is that ants are principally attracted to take moist baits, so for products to remain effective they have to stay in a semi-liquid form for longer, compared to cockroach gels where the pests will continue to take a palatable bait long after it has dried.

In my trials this summer, German cockroaches continued to find Advion Cockroach Gel bait that had been in-situ for over 12 months suggesting that the gel remained highly palatable, and completely effective in delivering 100% control.

There is definitely a clear difference in the palatability between the different gel bait formulations, and between the behaviour of different pest species and populations.
We would always advocate that operators trial different products in their specific situations, and find which one works most reliably for them.

Target pest ID

Identification of the target pest is important, since some gel bait formulations are more active on some species than others, particularly with ants. Cockroach gels are more accepted, with Advion Cockroach Gel effective against all major UK species, including German, American and Oriental species, for example.

With all ant gel baits more susceptible to drying out and losing attractiveness to ants, bait can also be put into protective capsules to retain moisture. Capsules could be bespoke bait stations, or simple drinking straws or small plastic vials fixed in place where ants are active. However, more frequent reapplication may be necessary.

For ant colonies, operators will sometimes combine an initial spray application for rapid knock-down of populations, followed up by gel bait application. However, in my experience, this approach has a risk of stopping ants feeding on gel baits for several days, and even of triggering an ant colony to split up - which may give a temporary respite, but greater problems in the long run.
Wherever possible, a useful approach with cockroaches is to physically hoover as many as possible from the environs, to reduce initial numbers, and then applying Advion Cockroach Gel where there is activity.

Secondary cascade

The formulation of the gel bait is important, since for ants you want to get as much as possible adhered to the workers and carried back to the nest, where other clean and feed nesting ants are to achieve a cascade effect of secondary kill.

With cockroaches, the aim is to give pests that have consumed bait time to get back to their harbourages, where they will die. The cannibalistic nature of cockroaches means they will eat the dead pests, and thereby consume a lethal dose of insecticide.

My research has calculated that, for each cockroach killed directly by Advion Cockroach Gel, up to 60 other roaches can be controlled through this secondary effect.

Customers need to be aware that whilst the initial numbers of cockroaches will start to decline soon after they feed, it can still take weeks for the cascade effect to work through the population.

However, the end result with Advion Cockroach Gel is almost always total control of the existing population.


In addition to the formulation of a gel bait, professionals need to consider the active ingredient it includes. Some gel baits contain a broad-spectrum insecticide, such as imidacloprid and fipronil.

The active indoxocarb, as in both Advion Cockroach and Advion Ant Gel, however, is effectively differentiated by target and non-target organisms. Thanks to its unique mode of action, the indoxocarb molecule is only converted into its insecticidal form by interaction with enzymes in the target species’ gut. Once activated, the molecule then binds to the target site inside the insect, to block its cell sodium channels. The insect experiences paralysis, followed by death.

Since other non-targets are unable to efficiently convert indoxocarb, if they were to inadvertently ingest bait it would be unlikely to have any serious detrimental effect.
That makes the Advion gel baits particularly well suited to use in homes, factories and food preparation areas, following the label instructions.

Active switching

My recent discussions with professionals indicates few consider the importance of active ingredient rotation to reduce the risk of resistance developing in cockroaches – despite related experiences with rodenticides. Fortunately, ants do not develop a resistance.

Where a single gel bait active is used repeatedly in the same situation, any mutations of pest populations that are less susceptible to an active could quickly increase in number.
If one brand appeared to be less effective, there is little point switching to another brand with the same active.

While we have seen no reduced efficacy or resistance to indoxocarb in Advion gel baits, it is good practice to rotate product use and actives in any cockroach population over a period of time.

Gel baits remain a key tool for targeted control of insect pest populations. Better understanding of how the different formulations and actives work, and how that can be utilised in practice, will ensure operators consistently achieve the best possible results for customers.

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Source: PPC93

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