Only problem if you need to feed them the plants. Sunlight helps to break it down, not water. up to 16 days, but it can last longer because some of it goes into the plant.http://www.livingwithbugs.com/PDFiles/mfs13.pdf
EFFECTS ON THE ENVIRONMENT
Leaf persistence: Spinosad is partly taken up by leaf tissue and this
enhances its effectiveness over time. Dry surface residues do little harm to
non-plant feeding insects. Spinosad residues on the leaf surface are be
broken down by sunlight. Half-lives for spinosyn A were 1.6 to 16 days
depending on the amount of sunlight received (Saunders and Brett 1997).
Fate in water: When spinosad is applied to water, very little breakdown
(hydrolysis) occurs, and it can be persistent. However, in water exposed to
sunlight, photodegradation occurs rapidly (Saunders and Brett 1997). In the
absence of sunlight, the half lives of spinosyn A and D are at least 200
Soil Persistence: Soil microbes degrade spinosad into other spinosyns that
can persist in the soil for several months and remain biologically active.
Repeated applications could lead to some build-up of spinosyns in soil. A
10-month field study in California and Mississippi showed that no degradation
products were found in soil below 24 inches (Saunders and Brett 1997).
SPINOSAD MATERIAL FACT SHEET
142 ORGANIC RESOURCE GUIDE
Leaching: Spinosyn A is more water-soluble than the other component of
spinosad, spinosyn D, and therefore was the subject of soil mobility studies.
However, spinosyn A and its soil metabolites bind to soil and have low soil
Wildlife: Spinosad shows slight toxicity to birds, moderate toxicity to fish,
and slight to moderate toxicity to aquatic invertebrates. It is highly toxic to
bees in laboratory tests and is highly toxic to oysters (US EPA 1997 a,b) and
other marine mollusks (Dow 2001).
Beneficial insects: Care must be taken when applying spinosad while honeybees
are foraging; after residues dry (a few hours) it is far less toxic to
bees (Bret et al. 1997). Spray droplets can also harm Trichogramma wasps
and other parasitoids (Suh et al., 2000; Tillman and Mullrooney, 2000; Bret
et al., 1997). However, once the deposits dry, they are generally safe for
beneficial insects. Studies in sweet corn have shown spinosad to be very
effective against the European corn borer, while conserving its natural
enemy complex (Musser and Shelton, 2003).
Other non-targets: Effects of spinosad on earthworms and soil microorganisms
have been investigated in the laboratory. Results indicated that application
rates of 25-150 g/ha should not cause significant effect on soil
microflora respiration. Earthworms were not very susceptible to spinosad
(LD50 > 970 mg/kg, Jachetta 2001). There is little research on the impact of
spinosad on insect soil detritivores and their predators, including ants and
springtails. However, since some spinosad products are targeted against
fire ants, a soil dwelling species, it is likely that there would be some impact
against other soil fauna
Spinosad is principally toxic to plant-eating insects in the orders
Lepidoptera (caterpillars), Coleoptera (beetles), Thysanoptera (thrips), and
Diptera (flies). It is not a plant systemic, but will penetrate leaves to some
extent and therefore has activity against some leafminers. Spinosad is not
effective at controlling mites at normal use rates (Thompson et al., 2000;
Cowles et al., 2000; Tjosvold and Chaney, 2001), although at high rates or
in combination with some adjuvants it has miticidal activity (Gilrein 2004).