IntroductionThe development of a technique to transform Droso-philamelanogasterwith‘foreign’DNAin1982(RubinSseeAshburner,1989)raisedhopesthatsimilar methods, probably mediated by P-elements,would soon be available for other arthropods. Thisfundamental tool for genetic manipulation wouldencourage both basic research and application. Inpractice,ithasprovedtobefarmoredi†cultthanwasforeseen to transfer the technology of transformationfrom Drosophila to other insects, let alone otherarthropods (Handler et al., 1991, 1993; O’Brochta etal., 1991). Despite this, there has been a considerableawareness of just how useful such a technique couldbe,forbothresearchandappliedpurposes.The recent success in transforming medfly with theMinoselement carrying a whitegene (Loukeris et al.,1995b), and of Aedes aegypti with the Hermes andmarinerelements carrying the Drosophila melanoga-sterkynurenine hydroxylase gene (Jasinskiene et al.,1998; Coates et al., 1998), encourages the view thatmethodsforgenetictransformationofarthropodsotherthan Drosophilamight soon be routinely practical. Itseems timely, therefore, to consider the medium-termneedsforresearchandlong-termimplicationsoftheseadvances. We will consider these needs under threeheadings: immediate research priorities leading torobusttechniquesfortransformationofatargetarthro-pod; medium-term research once such has beendeveloped, and longer-term research required forsuccessful application. In practice, these researchprogrammes should not be strictly consecutive. Ontheoptimisticassumptionthatthetransformationtech-nology will be developed, then research towardsmedium-term objectives and serious consideration ofthe problems that application will raise need to beembracednow.The need for further fundamental researchEncouraging as the data reported in 1995 (Loukeris etal.,1995a)and1998(Jasinskieneetal.,1998;Coates etal., 1998) are, we must remember that they came onlyafter over 10 years of intensive e•ort and that theroutine transformation of any non-drosophilid arthro-pod is not yet a reality. Both research and appliedinterestsneedrobustmethodsforthetransformationoftargetspecies. We definetransformation asthe stableintegration of DNA into the germ-line of an organism;the DNA is usually, at least in part, ‘foreign’ to thespecies. We define robustness by the property thatanyone skilled in the art can carry out the procedure,as is the case with transformation of Drosophila,atechnique that has been performed in hundreds oflaboratoriesworld-wide.What are the research issues?1. The introduction of DNA into the germ-line.Thetechnique of choice is clearly microinjection of trans-forming DNA into preblastoderm embryos, such thatthetransformingconstructisthenincorporatedintothegermcells.ThisworkswellinsomeDiptera(McGraneet al., 1988; Elbetieha & Kaltho•, 1988; Morris et al.,1989; Boccaccio & Quesada-Allue, 1994) and someLepidoptera (Nikolaev et al., 1989; Peloquin et al.,1997), though it is not trivial in species with a toughchorion (Leopoldetal., 1996).For any otherarthropodthe method of DNA introduction must be developed onacase-by-casebasis.Forsomeorganisms,e.g.mites,parasitic wasps and tsetse fly, direct injection of DNAintotheovariesthroughthemother’sbodywallmaybenecessary (Presnail & Hoy, 1992, 1995; Odindo, 1988).