A simple and rapid technique for assaying toxicants in aphids

A simple bioassay technique has been developed in order to study the effect of toxic compounds on aphids. The technique involves dipping of leaves of a particular aphid host in a solution of the desired toxic compound contained in a vacuum flask. The flask is then connected to a vacuum source in order to remove the air from the intercellular spaces of the palisade and the spongy parenchymas of the leaves. Breakage of the vacuum and return to atmospheric pressure forces the test solution into the now empty intercellular spaces which are thus filled with the solution. The treated leaves exhibited a typical water-soaked appearance. The infiltrated leaves were then offered to the aphids. The above treatment did not affect either the structure of the leaves or the development of the aphid colony on them. Aphids grown on leaves infiltrated with water lived longer in comparison with controls. In addition, insects grown on leaves infiltrated with 27.5, 13.7 and 6.9 p.p.m. of the systemic insecticide heptenophos died after 1.5, 3.0 and 5.0 h, respectively. The bioassay technique described in this report has certain advantages: it is simple, fast and inexpensive and is especially suitable for short-term studies involving the effects of such chemicals as toxins, insecticides and other toxicants on aphids. It may also be used to study the effects of growth factors, hormones and special nutrients on aphid growth and possibly on other sucking insects.