"More research is needed, and also to follow what's happening overseas. In New Zealand no one is really looking in soils and the wider ecosystem for traces of these chemicals or metabolites of them. In Europe, especially the Low Countries, there are persistent traces in soil and water."
In New Zealand new chemicals have to be approved by the Environmental Protection Authority.
The National Beekeepers Association's technical committee submits to it on new registrations of pesticides and alterations to existing pesticide registrations and takes the role of advocacy for pollinator health on pesticides for the association.
It was hard to maintain bee health in some horticulture areas here, Mr Foster said, especially in autumn and winter when he and other beekeepers had unexplained losses.
"Substances like pesticides are, if not killing bees, likely depleting their immune systems and having an effect on colony growth and survival."
Neonicotinoid pesticides have been in New Zealand for about 20 years, and are many times more toxic than organophosphate pesticides.
They include a nicotine molecule that acts on insects' nervous systems, disrupting their behaviour.
A neonicotinoid sold overseas and designed to kill termites, for example, works by stopping them grooming, which leaves them open to other pathogens and fungi which eventually do the work of killing the termites.
Neonicotinoid substances are used in New Zealand to treat most maize and grass seed, Mr Foster said. When the seed germinates they remain in the plant's system to kill biting and sucking insects.
They can remain in soil for more than 18 months and migrate into water.
Neonicotinoid (neo-nic) sprays have a wide range of uses and applications, from applying to foliage to seed treatments, and are commonly found in treatments for killing pets' fleas.
But bees in New Zealand have other threats as well. There's the varroa mite, which has killed off many wild colonies, plus a range of other pathogens and viruses, and a reduction in the plants they need for nectar and pollen. When combined, these reduce the number of insect pollinators around.
Bees are also killed if spraying is done in sunshine hours when plants are in flower. Sticking agents used to help sprays adhere to leaves are toxic to bees.
So while a particular spray may be dubbed "bee friendly" it becomes toxic to foraging insects such as bees when combined with a sticking agent.
Mr Foster's bees and those of other nearby beekeepers were hard-hit when a neonicotinoid spray was used in a citrus orchard in flower a few years ago.
"I had bees nearby in a kiwifruit orchard and they got it in the pollen and nectar from the citrus flowers. It's possibly very much a chronic thing in New Zealand - we really don't know," he said.
New Zealand has not yet suffered the large-scale colony losses found in parts of the northern hemisphere. Countries with colony losses have had these factors operating in combination for longer and New Zealand has the advantage and opportunity of learning from their mistakes and from their remedies.
This country's isolation from continental land masses is another advantage. New Zealand has a greater capacity than most countries to protect honey bees from the arrival and spread of new diseases - by prohibiting the entry of all bee products - and to eradicate some diseases completely - such as the goal of the American foulbrood programme.
But unlike continental countries, New Zealand has the disadvantage of being vulnerable to honeybee losses because there are fewer non-Apis (bee) pollinators available. Mr Foster said the country would benefit from investigating the global issues and proactively putting in place the types of remedies that were working elsewhere: "The National Beekeepers' Association is in the forefront of advocating for this."