Pesticides and Phytomedicine / Pesticidi i fitomedicina

Improvement of rodent pest control strategy: II - Response of wild brown rats to baits containing preservative previously exposed to unfavourable environmental conditions

2024-12-26T12:19:14+01:00

Control of brown rats (Rattus norvegicus) is an indispensable measure of protection of
human population and domestic animals, aimed at preventing the spread of infectious
diseases, and a measure of protection of goods and commodities that the brown rat
can damage by its presence and activities. Rodent control procedures in environments
with unfavourable conditions, such as high temperature and humidity, may fail due to
reduced bait palatability caused by its degradation. Baits were prepared based on OEPP/
EPPO recommendations, while ECHA recommendation was followed for bait exposure to
unfavourable environmental conditions. Placebo baits were prepared by mixing ground
maize grain and paraffin. Test baits, made by mixing the placebo bait with sorbic acid, were
exposed to unfavourable environmental conditions (temperature 30-35 ⁰C and humidity
90-95%). Brown rats previously captured from a wild population were used as the test
organism. After an acclimation period, the animals were subjected to a four-day choice
feeding test in which they were simultaneously offered placebo and test baits. The average
bait palatability was unchanged, and the palatability of bait containing the preservative was
48.85 %. Furthermore, the preservative had no influence on bait consumption, compared
to baits in the pre-test period, as there was no statistical difference in total amounts of bait
consumed in the tests. The results indicate that 1% sorbic acid can be used as a potentially
good additive to baits that are planned to be used in sewage systems and other areas where
unfavorable environmental conditions prevail and there is a risk of rapid mold development
and bait decay.

The longevity of two types of cereal carriers for rodenticide baits under adverse environmental conditions

2024-12-26T12:19:14+01:00

The protection of quality and safety of stored products requires adequate and
regular measures of protection from harmful rodents. Poisonous baits in a variety of
formulations, primarily those based on cereals, are the most widely applied method of
rodent control. Providing rodenticide baits that are durable over extended periods of time under adverse environmental conditions is an evident challenge for successful rodent control.
The present study focused on examining the effects of particle size of maize- and
wheat-based rodenticide bait carriers on bait longevity under unfavourable environmental conditions. Maize and wheat grain fractions with particle sizes <0.8 mm, 0.8-1.25 mm, 1.25-2 mm and >2 mm were kept in a climate chamber for 33 days at temperature varying from 30-35 C˚ and humidity from 90-95%. Baits containing different grain fractions, and supplemented with 1% sorbic acid, were tested for mold development. The same grain fractions without the preservative were used as control baits. Test and control baits were exposed to identical environmental conditions in the climate chamber over the same time period.
Mold development on preservative-free baits was considerably faster and more
intensive, compared to baits that contained sorbic acid. Initial signs of mold development on control baits were observed as early as on the third day of testing. Carrier type and fraction size affected mold development significantly. Regarding maize-based baits, mold development was more intestive on grain fractions >1.25 mm, compared to wheat-based grain which enabled more intensive development of mold on fractions with particle size <1.25 mm.

Demografic analysis of biopesticide effects on the two-spotted spider mite (Acari: Tetranychidae) following egg treatment

2024-12-26T12:19:14+01:00

The effects of biopesticide products based on oxymatrine, azadirachtin and Beauveria
bassiana (strain ATCC 74040) on demographic parameters of the two-spotted spider mite,
Tetranychus urticaeKoch (Acari: Tetranychidae), were evaluated in laboratory bioassays. The
biopesticides were applied by spraying 24 h old eggs laid on bean leaves, using the following
concentrations: 50 μl/l (oxymatrine-based product), 0.75 g/l (azadirachtin-based product)
and 3 ml/l (B. bassiana-based product). These concentrations were within 95% confidence
limits of the LC50s estimated in acute toxicity bioassays. The mites that hatched from treated
eggs completed their juvenile development on the same leaf discs, i.e. the toxic effect was
caused by topical treatment and residual exposure. When the surviving females entered
their preovipositional period, cohorts of 40 control and 40 treated females were transferred
to untreated leaf discs (1 female/disc). Females were transferred daily to new discs until
the death of the last one. Using the data on their age-specific survival and age-specific
fertility (production of female offspring), the following demographic parameters were
estimated: gross reproductive rate (GRR), net reproductive rate (R0), intrinsic rate of increase
(rm), finite rate of increase (λ), and mean generation time (T). The biopesticides significantly
affected these demographic parameters in females that survived treatments. All three
biopesticides significantly reduced the GRR and R0 values. In the bioassays with oxymatrineand
azadirachtin-based products, the rm and λ values were reduced by 22% and 5%, and
16% and 4%, respectively, due to reduced survival and fertility, as well as extended juvenile
developmental time of females that survived treatment, compared to control females. In
the bioassay with the B. bassiana-based product, the rm and λ values were reduced by 7%
and 2%, respectively, mostly due to the reduced survival of treated females. The oxymatrineand
azadirachtin-based products significantly extended, while B. bassiana-based product
reduced the T values.