Neonicotinoids case study Flashcards
What are neonicotinoids?
Water soluble insecticicides which are synthetic derivatives of nicotine (alkaloid compound). Systemic insecticides that translocate through plant tissues following application.
They are used to control sucking insects and some chewing insects- generally applied to crops and soil as seed treatment- but maybe used as a spray
How do neonicotinoids work?
In insects they act on post-synaptic acetylcholine receptors in the central nervous system.
Neonics do notdistinguish between pests and “good” insects; e.g. honeybees, bumblebees, predatory ground beetles and parasitoid wasps.
Why have neonics grown in popularity?
Insects have developed resistance to organophosphates, carbamates and pyrethroids- and it opened the market for neonics. Today, nearly 30% ofthe insecticide market is neonics.
Often applied as seed treatments- systemically taken up by the plant- it can be present in all plant parts including nectar and pollen.
Big 3 of neonics- Imidacloprid, Clothiandin, Thiamethoxam.
Ban of neonics
Use of most neonics was restricted in 2013 (EU), but now emergency application in England of ‘Cruiser SB’ pesticide which contains Thiamethoxam is allowed. In 2006 in UK, Imidacloprid was widely used on wheat, oilseed rape (OSR), linseed, triticale and sugar beets
Most used on:
1) Sugar beets
2) Wheat
3) OSR
Concerns about neonics?
Most of the concerns has been about bees and the decline in no. of pollinators because of the importance of these creatures. An aspect that is relatively ignored is the effects of neonics in soil.
Oral LD50 for imidacloprid for bees is 3.7 - 40.9 ng per bee. Sub lethal effects include altered reflex responses, altered learning responses, altered ability to combat other stressors.
Shmuck et al (2001) found imidacloprid levels of 1.5μg/kg in pollen and nectar from sunflowers grown in soils containing 18μg/kg imidacloprid.
Bees would need to consume 2.6mL of nectar to obtain the LD50 dose but its possible over time, but neonics have sub lethal effects on the bees that make it less able to cope with disease, lack of food, bad water.
Half life of neonics in soils?
Half lives depend upon amount of organic matter and other factors, but half lives in literature are:
1) Imidacloprid: 28-1250 days (across the world). In the UK it is 1233-1268 days- but Jones et al. (2014) suggest 440-560 days in England, but they guessed the original application late.
2) Clothiandin: 148- 6931 days, but Jones et al. (2014) suggest 37-78 days (based on data from just 4 fields in England)
3) Thiamethoxam: 7-353 days.
Effects of neonics on honeybees and bumblebees?
It is accepted now that neonics affect honeybees and bumblebees. The EU implemented a temporary ban on use of neonic seed dressings for flowering crops on 1st December 2013.
A study of neonic residues in honey was carried out before the ban and a year after the ban. Residues were found in 1/2 the samples before the ban and in over 1/5 a year after the ban. Clothiandin was most frequently detected.
Nenonics conc. declined from May-Sep after the ban, but spikes in early year coincide with OSR flowering, suggest OSR contained residues carried over from previous winter cereal crop.
