A diverse range of novel molecular (DNA) markers are now available for entomological investigations. Both DNA and protein markers have revolutionized the biological sciences and have enhanced many fields of study, especially ecology. Relative to DNA markers, allozymes are cheap, often much quicker to isolate and develop, even from minute insects (aphids, thrips, parasitic wasps, etc.), and subsequently easy to use. They display single or multi-locus banding patterns of a generally easily interpretable Mendelian nature, and the statistics for their analysis are well established. DNA markers are also suitable for use with small amounts of insect material and can be used with stored, dry or old samples. They have an expanding range of applications, many involving intra- and interspecific discriminations. Like allozymes, they can be single or multilocus, whilst methods for their statistical analysis have recently been published. However, they can be considerably more expensive than allozymes, require more complex preparatory protocols, expensive equipment, may involve lengthy development procedures (e.g. isolating cloned oligonucleotides to develop primers to detect microsatellite regions) and some have complex multi-locus banding patterns which may be of a non-Mendelian nature (e.g. RAPDs, randomly amplified polymorphic DNA), and are in some cases, not easily repeatable. In this review, we hope to inform the general reader about the methodology and scope of the main molecular markers commonly in use, along with brief details of some other techniques which show great promise for entomological studies. Thereafter, we discuss their applications including suitability for particular studies, the methods used to load and run samples, subsequent band detection, band scoring and interpretation, the reliability of particular techniques, the issues of safety involved, cost effectiveness and the statistical analyses utilized.

The parasitic Nematomorph hairworm,Spinochordodes tellinii(Camerano) develops inside the terrestrial grasshopper,Meconema thalassinum(De Geer) (Orthoptera: Tettigoniidae), changing the insect's responses to water. The resulting aberrant behaviour makes infected insects more likely to jump into an aquatic environment where the adult parasite reproduces. We used proteomics tools (i.e. two-dimensional gel electrophoresis (2-DE), computer assisted comparative analysis of host and parasite protein spots and MALDI-TOF mass spectrometry) to identify these proteins and to explore the mechanisms underlying this subtle behavioural modification. We characterized simultaneously the host (brain) and the parasite proteomes at three stages of the manipulative process, i.e. before, during and after manipulation. For the host, there was a differential proteomic expression in relation to different effects such as the circadian cycle, the parasitic status, the manipulative period itself, and worm emergence. For the parasite, a differential proteomics expression allowed characterization of the parasitic and the free-living stages, the manipulative period and the emergence of the worm from the host. The findings suggest that the adult worm alters the normal functions of the grasshopper's central nervous system (CNS) by producing certain ‘effective’ molecules. In addition, in the brain of manipulated insects, there was found to be a differential expression of proteins specifically linked to neurotransmitter activities. The evidence obtained also suggested that the parasite produces molecules from the family Wnt acting directly on the development of the CNS. These proteins show important similarities with those known in other insects, suggesting a case of molecular mimicry. Finally, we found many proteins in the host's CNS as well as in the parasite for which the function(s) are still unknown in the published literature (www) protein databases. These results support the hypothesis that host behavioural changes are mediated by a mix of direct and indirect chemical manipulation.