Effects of soil applications of imidacloprid on adult green lacewing (Chrysoperla carnea)

Imidacloprid is a systemic insecticide with soil, foliar and seed uses for control of sucking insects, including aphids, thrips, whiteflies and fungus gnats in the greenhouse. It is also used by botanical gardens, nurseries and golf courses to control white grubs feeding on roots, foliar feeding insects and borers that feed directly under tree bark. Imidacloprid is part of the neonicotinoids class of insecticides and acts upon the nervous system, causing blockage of postsynaptic acetylcholine receptors (Ware 2000).

The objective of this experiment was to investigate the effects of soil applications of imidacloprid (Marathon 1G) on adult lacewings used for biological control in the greenhouse. Chrysoperla carnea larvae are generalist predators, and attack eggs and soft-bodied insects such as aphids, spider mites, whiteflies and thrips among others. Adults feed on nectar, pollen and honeydew. When provided with these, the lacewing adults will live longer and lay more eggs (Rincon-Vitova Insectaries 2005). A feeding test was set up in which adult lacewings in cages were fed nectary flowers from treated Fagopyrum esculentum, buckwheat, and Asclepias curassavica, milkweed. We found that imidacloprid was highly toxic when ingested via plant nectar and pollen to adult lacewings. Mortality was greater amongst populations of lacewings fed from treated plants than for control plants. 
 

Materials and Methods
Three thousand lacewing adults, Chrysoperla carnea, were obtained from Rincon-Vitova Insectaries of Ventura, California for the whole experiment. Approximately one thousand lacewing adults were used every replication. The lacewings arrived inside a paper container and distributive in nine mesh cages (30cm x 30cm) for the first replication and twelve mesh cages (30cm x 30cm) for the second and third replication. Upon release, cages were provided with lacewing diet, four tubes with water, four tubes with honey-water and two untreated flower head of Asclepias currissavica, Mexican milkweed and annual buckwheat Fagopyrum esculentum. The cages were cleaned and provided with water, honey-water, lacewing diet, and flower heads daily until the experiment started.

The experiment was examined in Asclepias currissavica, Mexican milkweed and annual buckwheat Fagopyrum esculentum. Neotropical Mexican milkweed is strongly recommended to use in conservatories, butterflies garden and nectar feeder (Missouri Department of Conservation 2005). Mexican milkweed has small, open flowers comprising an umbel on which lacewing adults can easily feed. Annual buckwheat, Fagopyrum esculentum, is commonly used in organic production to provide shelter and flowers with nectar for beneficial insects, such as lady beetles, parasitoids, minute pirate bug, Orius insidiousus and lacewing Chrysoperla carnea (University of Connecticut 2005). One hundred forty four cutting of Asclepias currissavica, Mexican milkweeds were purchased from Tropilab, Inc. and transplanted in six inch pots and two hundred forty four seeds of Fagopyrum esculentum were sowed in six inch pots.

Through all three replications, behavioral changes were observed in lacewing adults in 1x and 2x treatment that were not significant in any of the control cages, expressed as reduction of movement and flight inability of lacewing adults. Affected lacewings were not able to continue feeding or able to defend themselves against larvae that persisted in the cages, suggesting a sub-lethal effect of imidacloprid. Egg production in 1x and 2x were observed to be lower than that of control cages. However, eggs were not counted for this experiment; this could be included in future research. 

References
Missouri Department of Conservation. 2005. Butterfly Gardening and Conservation. http:/www.conservation.state.mo.us/nathis/insects/butterf/.

Rincon-Vitova Insectaries. Green Lacewing Technical Bulletin. 2005.
http://www.rinconvitova.com/lacewing.htm#Green%20Lacewing%20Technical%20Bulletin.

University of Connecticut, 2005. Integrated Pest Management. http:/www.hort.uconn.edu/ipm/general/htms/cvercrop.htm.

Ware, G. 2000. The Pesticides Book. Thomson Publications. Fresno, California