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Lacewings are attracted by a solution in the bottle and over-winter within the straw chambers |
The green lacewing (Chrysoperla carnea)
is the most important lacewing with regards to its impact on arthropod pest
populations in agricultural ecosystems and systems, and for this reason is
greatly used in biological control. A single adult female is able to produce
several hundred eggs and each emerging larvae is capable of consuming several
thousand prey insects (such as aphids, whitefly, thrips) during its lifetime(1).
Observations of lacewing biology form the basis of the
present work. Firstly, adults locate suitable habitats and hosts by responding
to chemical cues (semiochemicals)(2,3) and secondly lacewings need to find a
suitable habitat in which to survive the winter in a semi-active physiological
state known as diapause. Diapause comes about in response to changes in the day
length and temperature, and is accompanied by a change in the colour of the
insect from green to yellow-brown. Recorded sites for diapause include unheated
parts of houses, stables and barns, the underside of bark, leaf-litter and
abandoned wasps nests, and large clusters can be found at such sites(4).
Chambers colonised
Our project evaluates artificial chambers which mimic
normal diapause sites, and which incorporate attractive colours and chemicals
into their design in order to maximise the rate of lacewing colonisation.
The study includes an intensive field testing programme to
assess the chambers in olive groves in southern Spain and pastureland in West
Wales. A variety of sites are necessary because the species contains
geographical variants which may behave differently. The Spanish work has the
advantage that olive producers are keenly searching for pest controls that do
not rely on pesticides and the project thus taps a potentially lucrative market.
Chambers have been in the field for several weeks and early
results indicate that they are being colonised by lacewings. The chambers will
be stored in the lab during winter and returned to the field next spring, thus
releasing lacewings early in the season just as pests are appearing. The crops
will be sprayed with a food solution of yeast, sugar and water in the ratios
4:7:10 to provide the protein-rich material the insects require to mature eggs.
The chambers will subsequently act as portable pest control units to assist in
the control of insect pests in agricultural, horticultural and glasshouse
systems.
The present work is a pilot study and
further work may be required on the chamber design and attractant development
before a product is commercially available. Manipulation of natural enemy
populations using semiochemicals in this way is likely to be an increasingly
important area of investigation for entomologists over the next few years.
References
1. Canard, M. and Principi, M.M., Life Histories and Behaviour. In: Biology of
the Chrysopidae (eds. Canard, M, Séméria Y, New, T.R.) Dr. W Junk Publishers,
The Hague, Chapter 4, 1984.
2. Hagen, K.S., Greany, P., et. al., Tryptophan in Artificial Honeydews as a
source of an attractant for adult Chrysopa carnea, Env. Ent. 5, 1976, 3:458-468.
3. McEwen, P.K., Jervis, M.A., Use of sprayed L-tryptophan solution to
concentrate numbers of the green lacewing Chrysopa carnea in olive tree canopy.
Ent. Expt. et Applicata, 1994, 70:97-99.
4. op. cit. 1.
The work is supported by a Welsh Office Regional Enterprise Grant to Peter Rossiter, Insect Habitat, Ty Pellaf, Pant-y-deri, Boncath, Dyfed SA37 OJB.
The author wishes to thank the Dyfed Wildlife Trust, The Biodynamics Centre, Dyfed and the consèjo Superior de Investigaciones Cientificas, Granada, Spain for the use of their field sites.
School of Pure and Applied Biology,
University of Wales, Cardiff, UK, Tel. +44 (0)1222 483861.
[This
article first appeared in Pesticides News No. 30,
December 1995, page 18]