Some ecological implications of a neem (azadirachtin) insecticide disturbance to zooplankton communities in forest pond enclosures.
A neem-based insecticide, Neemix 4.5, was applied to forest pond enclosures at concentrations of 10, 17, and 28 microg l(-1) azadirachtin (the active ingredient). At these test concentrations, significant, concentration-dependent reductions in numbers of adult copepods were observed, but immature copepod and cladoceran populations were unaffected. There was no evidence of recovery of adult copepods within the sampling season (May to October). The ecological significance of this disturbance to the zooplankton community was examined by determining biomass as a measure of food availability for higher predators, plankton community respiration, dissolved oxygen (DO) concentrations, and conductivity as functional indicators of ecosystem stress, and zooplankton food web stability as a measure of effects on trophic structure. The selective removal or reduction of adult copepods was sufficient to measurably reduce total zooplankton biomass for several weeks mid-season. During the period of maximal impact (about 4-9 weeks after the applications), total plankton community respiration was significantly reduced, and this appeared to contribute to significant, concentration-dependent increases in dissolved oxygen and decreases in conductivity among treated enclosures. The reductions in adult copepods resulted in negative effects on zooplankton food web stability through eliminations of a trophic link and reduced interactions and connectance. Comparing the results here to those from a previous study with tebufenozide, which was selectively toxic to cladocerans and had little effect on food web stability, indicates that differential sensitivity among taxa can influence the ecological significance of pesticide effects on zooplankton communities.
Kreutzweiser
David P
DP
Canadian Forest Service, Natural Resources Canada, 1219 Queen Street East, Sault Ste. Marie, Ont., Canada P6A 2E5. dkreutzw@NRCan.gc.ca
Sutton
Trent M
TM
Back
Richard C
RC
Pangle
Kevin L
KL
Thompson
Dean G
DG
D000704:Analysis of Variance; D000818:Animals; D018533:Biomass; D033361:Cladocera / Q000187:drug effects; D033342:Copepoda / Q000187:drug effects*; D017753:Ecosystem; D004553:Electric Conductivity; D020387:Food Chain; D005618:Fresh Water / Q000032:analysis; D006863:Hydrogen-Ion Concentration; D007306:Insecticides / Q000633:toxicity*; D036701:Limonins / Q000633:toxicity*; D010100:Oxygen / Q000032:analysis; D010101:Oxygen Consumption / Q000187:drug effects; D013696:Temperature; D015048:Zooplankton / Q000187:drug effects*
D007306:Insecticides; D036701:Limonins; C010329:azadirachtin; D010100:Oxygen