Pest control| PPC97 November 2019
Partho Dhang has a PhD in Zoology and is the author of ‘Urban Pest Control: A Practitioner’s Guide’, where he explores trends in the industry, pest control tools, and sustainable pest management.
In this exclusive article for PPC, Partho explores the intricacies of insecticide baits, giving practical insights for UK pest management professionals.
SPEED VIEW
- Baits are generally safer than sprays as they have low levels of active ingredients
- Baits designed to attract one species rarely attract other pests
- By coprophagy and necrophagy, leftover insecticide is taken up by others in the infested location, causing secondary kills
- After eight months, cockroach populations decreased about 80% in IPM units, compared with a 300% increase with conventional treatments
- The human component involved in baiting is possibly the factor against its effectiveness, possibly resolved by training.
Indoor pests have habituated themselves with human food and items we leave lying around, thus making use of insecticide baits has turned out to be most advantageous and effective.
As we know, pests find harbourage in homes for food and shelter.
The concept of baiting has taken these two aspects and turned it into a practical technique.
A pest controller now provides bait as a food substitute, and bait stations as shelter to replicate both of the pests needs.
Another reason bait has become popular is reduced risk and higher safety qualities when used correctly.
Reducing risk with bait
Baits are generally safer than spraying as they make use of very little active ingredients in their formulation.
The amount of active ingredient varies between 50mg to 2.0g per kilogramme of bait.
The application rate is also a few grammes of formulated bait per square metre of the treatment area.
This keeps both the application site and the applicator safe.
Most active ingredients used in insect baits are chosen to have low mammalian toxicity and are target specific.
They are not usually contact poisons and are mainly analogues and antagonists of insect growth regulators (IGR) such as juvenile hormone (JH), ecdysone, chitin synthesis inhibitors and related compounds.
Most active ingredients used in insect baits are chosen to have low mammalian toxicity and are target specific.
Partho Dhang
Each of these generation compounds has low toxicity to mammals, or selective toxicity towards insects, therefore making bait handling safe.
But there are instances where toxic active ingredients are also used in baits to give a quick killing effect.
In such cases, the percentage of active used in the formulation is kept at a level which is many times lower than conventional spraying.
Baits are target specific - baits made for one pest species rarely attract another pest species.
This prevents affecting non-target organisms that may also be around.
This is achieved by using pest-specific attractants and stimulants.
In addition, baits should always be applied or placed in selective areas or inside concealed bait stations which prevent non-target organisms coming in contact.
These two aspects lower the risks of bait when applied.
Baits work by a single process of ingestion - a precise act on the part of the pest.
While conventional spraying requires the pest to come into contact with the chemical.
To achieve this, baits need to be selectively placed, whereas for spraying the entire area is treated.
Thus the amount of active ingredient used in baits can be very small.
The inner workings of bait
Baits developed for insect pests are food based.
They have not only been effective in killing the insect directly through ingestion by the feeding individual, but also showed a killing effect on individuals that did not ingest the bait directly.
The process termed ‘transfer effect’ or ‘secondary effect’ further enhances the efficacy of the bait against insects which are social or live in groups and exhibit trophallaxis or proctodeal feeding.
Cockroaches are not social insects but live in groups, therefore bait works well with them.
Cockroaches have shown a horizontal transfer of insecticides contained in baits and there is much research to demonstrate this fact (Kopanic and Schal, 1997; Buczkowski et al, 2001).
They have not only been effective in killing the insect directly through ingestion by the feeding individual, but also showed a killing effect on individuals that did not ingest the bait directly.
Partho Dhang
The process of secondary kill takes effect due to the presence of unmetabolized slow acting insecticide in the bait formulation, in the faeces, or oral secretions or it may simply remain in the body of the dead cockroaches.
By the process of coprophagy and necrophagy, leftover insecticide is then taken up by another group individual in the infested location, which brings about secondary kills.
Transfer effects or secondary kills increase the overall control efficiency of the bait; however the efficiency of the secondary kill can be dependent on the active ingredient and other influencing factors such as developmental stage, strain and donor/recipient ratio (Wang et al, 2008).
In one study, the researchers Bayer et al (2012) showed that cockroaches in fact consumed more active ingredient from a bait than needed to cause mortality proving there was no bait shyness.
The same work also estimated that a 30g tube of gel bait potentially killed from 394 to 6,966 adult cockroaches, depending on their species.
Mortality for all cockroach species was faster for adults (≥3 days) than for nymphs (≥7 days).
Similar successful bait transfers, from one individual to others in a colony, have been shown in controlling all forms of social insect pests such as ants, termites and wasps.
Are baits advantageous over conventional sprays?
It remains an unchallenged fact that conventional methods of pest control have eased urban life of humans, but it has also brought enormous damage to health and the environment.
Conventional methods of pest control can cover a wider range of pests, provide quick and easy elimination and have long field persistence as key benefits.
Conventional methods depend on the use of pesticides as a single approach to pest control, in which the chemical provides significant or acceptable reduction in the pest population.
It involves a single action of a chemical application following some regular, predetermined spray schedule.
However, modern pest management is more than just eliminating pests. It involves maintaining control over pests, preventing re-infestations and reducing chemical use as being more important than mere killing (Dhang, 2011).
Baits have provided a rational solution to all the above and, in addition to being able to control cryptic pests, have allowed treatment to inaccessible and sensitive areas.
In addition baits offer no odour, no translocation, and no staining potential, which are all common household concerns. Baits also leave lower or no residues.
Furthermore, baiting is most suitable for treating sensitive locations such as high-density human population, food preparation areas, inside hospitals and schools.
It is another aspect, such as cost of services and overall efficacy, which make baits advantageous over conventional sprays.
A World Health Organization (Europe) publication provides some insight into it (Rust, 2008): it reported in one instance that the cost for a conventional service of cockroach control was US$8.57 (£6.79) per unit and IPM was US$7.49 (£5.93) per unit.
In another study, the costs for IPM involving monitoring, baiting, cleaning and structural repairs were US$46-69 (£36-55) per unit in the first year and US$24 (£19) per unit in the following year.
In comparison, conventional chemical controls cost US$24-46 (£19-36) per unit, and involved no repairs or structural modifications to the apartments.
In another study in public housing, the costs of conventional crack-and-crevice treatments with sprays and dusts were compared with vacuuming, baits and insect growth regulators (IGRs) for controlling German cockroaches.
The average costs for IPM and conventional treatments were US$4.06 (£3.64) and US$1.50 (£1.19) per unit, respectively. After eight months, cockroach populations decreased about 80% in IPM units, compared with a 300% increase with conventional treatments.
What are the methodologies involved in baiting?
Compared to conventional spray treatment, baiting is inspection-driven, friendlier to the environment, and often more effective.
Though the technology is restricted to a few pests, it has made significant progress as a tool in urban pest management.
However, as discussed by Dhang (2011) the overall efficiency of baiting will depend on the bait applicators.
Applicators’ knowledge and skills are of paramount importance for baiting to be successful, as the concept of baiting is a dynamic field, constantly evolving and adjusting to changes in insect behaviour and location.
The human component involved in baiting is possibly the single factor against its popularity among pest control practitioners, which could be resolved by training.
The critical part of a typical baiting programme depends on the following:
Commercial bait varies in attractability, nutritional quality, colour, texture, moisture and many other factors which are critical to acceptability and sustained feeding. For best performance, bait needs to be tested before use.
- Technical skills and knowledge of the bait applicator
This is the second most important factor in bait performance. Good bait but poor placement and wrong dosage can make bait ineffective. The greatest variant in any baiting program is the quantity of bait consumed. Knowledge of pest biology is often required to overcome this issue.
It is never possible to determine the pest population based on a survey or inspection. Often the population of the pest determines the bait quantity, the number of visits and ultimately the cost. This has to be thoroughly noted before starting a baiting programme.
Baits will only work if they are ingested, which is always a voluntary act. A pest will not walk an extra mile to seek a bait when food is around the harbourage. To make baits competitive it is thus important to either aggregate the pest in a specific location, using a bait station or place the bait in the regular feeding zone near the harbourage.
Baits or a baiting programme does not work well if the sanitation of the site is poor. Leftover food or alternative food available on site acts as temptation away from the bait, reducing its consumption and in turn becoming ineffective in the elimination of the pest. Thus it is advisable to clean the site before baiting.
- Follow-ups and monitoring
One time bait application does not often work. Too much bait left may turn dry, get contaminated, and thence be unfit for sustained consumption. Too little will not kill all individuals in the group. This makes a repeat visit a must.
References
Bayer BE; Pereira RM and Koehler PG, 2012. Differential consumption of baits by pest blattid and blattellid cockroaches and resulting in direct and secondary effects. https://doi.org/10.1111/eea.1200
Buczkowski G, Kopanic RJ and Schal C, 2001. Transfer of ingested insecticides among cockroaches: effects of active ingredient, bait formulation, and assay procedures. Journal of Economic Entomology 94, 1229-1236.
Dhang P, 2011. Insect Bait: Technology to Manage Urban Pest with less Insecticide. In: Dhang P (ed.) Urban Pest Management: an Environmental Perspective. CABI, London,pp. 187-206.
Dhang P, 2018. Urban Pest Control: A Practioner’s Guide. CAB International, Oxfordshire, UK, pp 98-107.
Kopanic RJ Jr and Schal C, 1997. Relative significance of direct ingestion and adult-mediated translocation of bait to German cockroach (Dictyoptera: Blattellidae) nymphs. Journal of Economic Entomology 90, 1073-1079.
Rust M, 2008. Cockroaches. In: Bonnefoy X; Kampen H and Sweeney K (eds) Public Health Significance of Urban Pests. World Health Organisation Regional Office for Europe, Copenhagen, Denmark, pp.65.
Wang C; Yang, X; El-Nour MA and Bennett GW, 2008. Factors affecting secondary kill of the German cockroach (Dictyoptera: Blattellidae) by gel baits. In: Robinson WH and Bajomi D (eds.) Proceedings of the sixth International Conference on Urban Pests, Budapest, July 2008, OOK-Press, Budapest, pp. 153-159.
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Source: PPC97