I detected pesticides in (honey, pollen and bees ) collected during spring and summer and i need to assess if there is significant difference between spring and summer through pesticide frequency of detection.
You need to do plain hypothesis testing. Which test you should choose depends on you data. Without further infomation that is all I can tell you.
So you have only presence-absence outcomes?
A binomial outcome with a pool size of 1. Try using the software PooledInfRate written by Dr. Brad Biggerstaff. Try this link and download the appropriate file: http://www.cdc.gov/westnile/resourcepages/mosqSurvSoft.html.
The software will use your presence-absence data and calculate the probability that your next sample will be positive. It also gives a 95% confidence interval. If the intervals between spring and summer do not overlap then you have a significant difference. If the 95% confidence intervals do overlap, then it is unlikely that there will be a significant difference.
You have more choices if you have quantitative data.
if your data can be summarized as a 2x2 table (line = spring vs. summer; column = pesticide vs. no pesticide), each cell of the table containing the number of observations, you can use a chi-squared test (or an exact Fisher test available on-line in several sites like http://danielsoper.com/statcalc3/calc.aspx?id=29)
Yes, there could be a simple t-test, which serve the purpose, since only non-overlapping sets of data are there, ie., spring and summer, for comparison.
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