A look at the top research findings published in the last 12 months.
Below we summarise the takeaways from the latest research in this field.
New Cockroach Bait Active
Syngenta Professional Products in the US has announced a new active ingredient is in registration: isocycloseram, a broad-spectrum insecticide. Isocycloseram is a new isoxazoline insecticide, a GABA-gated chloride channel allosteric modulator. As a new mode of action (Group 30), isocycloseram will be a useful tool in resistance management both in the agricultural and professional pest markets. The insecticide will be marketed as Plinazolin technology, and in the professional pest control market, it will be utilised in cockroach gels under the Vanecto brand name.
Recent research published by Prof. Chow-Yang Lee and his team at the University of Riverside, California, has highlighted some of the performance benefits of this new insecticide. A cockroach bait formulation containing 1% isocycloseram proved to be comparable or superior in terms of speed of action and level of mortality when compared to a range of leading commercial products when tested on adult male cockroaches from a range of different strains. This included delivering nearly 100% control of the Ryan strain, which has demonstrated high levels of resistance to fipronil. It also delivered excellent secondary kill properties, with cockroach recipients having a mean survival time of 1.5 days.1
Bait transfer in cockroach populations
It is well accepted that one of the key reasons that cockroach baits deliver excellent population control is that they not only control cockroaches that feed on the bait, but also kill cockroaches through a transfer effect, when other cockroaches feed on the vomit and faeces of cockroaches that have previously ingested the bait. This is a secondary transfer effect. But the question is, can the cockroaches that ate the vomit or faeces containing insecticide subsequently pass on this insecticide in their own excretions too? This would be a tertiary transfer effect. Researchers have recently evaluated a range of commercial products for secondary, tertiary and even quaternary transfer effects.
The laboratory trials involved feeding bait to adult female German cockroaches and then exposing first instars to their dead bodies and faeces (for secondary kill).2 These dead nymphs and their faeces were exposed to further first instars to assess tertiary kill and so on. All the baits tested delivered 100% mortality of the adult females and a high level of secondary kill (average 85%). However, when it came to tertiary kill, only fipronil, indoxacarb, dinotefuran and emamectin benzoate baits provided some level of mortality (15-70%). Only fipronil and indoxacarb gave any level of quaternary kill. Although the nymph mortality at the quaternary level was less than 20%, this demonstrates a remarkable passage of insecticide through the population.
How do cockroaches respond to pyrethroids?
It is a commonly accepted belief that pyrethroids are repellent to cockroaches. But is this really the case? Researchers have taken a closer look at the response of cockroaches to pyrethroid-treated surfaces.
The study evaluated the response of cockroaches to a range of pyrethroids, as well as DEET and corn mint oil, by exposing the cockroaches to areas where they could choose between treated surfaces and control surfaces (only treated with acetone).3 The cockroaches readily moved over pyrethroid-treated surfaces (no different to the control) but were repelled by surfaces treated with DEET or corn mint oil. However, in a second trial where cockroaches were given the choice between two harbourages – one treated with pyrethroid and one untreated – the cockroaches preferred to rest in the untreated shelters.
The authors concluded that pyrethroids do not act as spatial irritants; they did not impact cockroach movement behaviour, but that they did have some impact as a contact repellent.
The authors noted that these trials were carried out using field-collected, pyrethroid-resistant cockroaches and it is unclear as to whether this impacts the perception of repellency, although since these were field-collected species, the effect observed would be similar to the effect observed in the field.
The authors further point out that these results impact the description and performance of a perimeter barrier treatment, noting that it may be unwise to consider such a treatment as a repellent barrier. Furthermore, it may be that the use of pyrethroids near cockroach gel baits does not impact bait feeding as previously believed, however this would need to be evaluated in trials.
1 Lee, S-H et al. (2024). Toxicity of isocycloseram, an isoxazoline insecticide, against laboratory and field-collected German cockroaches (Blattodea: Ectobiidae). Journal of Economic Entomology, 177(3): pp. 1086-1094.
2 Hamilton, J.A. et al. (2023). Cockroaches as Trojan Horses for Control of Cockroach Aggregations With Baits. Journal of Economic Entomology, 116(2).
3 Gaire, S. et al. (2023). Behavioral responses of field-collected German cockroaches to pyrethroids and pyrethroid-formulated insecticides. Pest Management Science, 80(2): 433-441.
