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.

Bemisia tabaci (Gennadius) is a pest of global importance which resists many conventional insecticides. Novel strategies for control are required and these may incorporate compounds whose lethal and sublethal effects have gone unremarked. Although most commonly employed as an insecticide synergist, piperonyl butoxide alone was lethal to predominantly second instar nymphs of the cotton whitefly, B. tabaci at LC50s of between 60 and 600 ppm, depending on the strain. Formulated and technical material were similarly toxic and far more so than detergents. Some strains exhibited slight tolerance (c. 3–10 fold) but there was no correlation of this with the presence of known resistance mechanisms or enzyme banding patterns. Residues of piperonyl butoxide alone were toxic to adult B. tabaci at c. 2000 ppm which was similar to the toxicity of paraffin oil. Piperonyl butoxide also increased developmental times among B. tabaci nymphs at doses as low as 10 ppm and exerted a transient effect on oviposition. There was strong evidence that it did not reduce the feeding activity of insects surviving treatment. Such effects offer scope for incorporating this compound into resistance management programmes, especially in conjunction with natural enemies (e.g, parasitoids active specifically against immature hosts).

The facultative ectoparasite, Lucilia sericata (Meigen) has been described as a pioneer colonizer of carrion. This behaviour is believed to enable it to escape the intense interspecific competition which can occur between dipterous larvae within carrion. Such escape is necessary as this fly species has been thought to have reduced competitive ability, resulting from its evolutionary progression towards parasitism. In the work reported here, the attraction of L. sericata to carrion bait at different stages of decomposition (fresh to 28 days old) was investigated in the field. Trials were run over three years, with carrion bait presented in the presence and absence of sodium sulphide. Decomposition had a significant effect on the numbers of L. sericata caught; more decomposed bait caught greater numbers of L. sericata than fresh bait. However, this effect was not apparent if sodium sulphide was added to the carrion. With sodium sulphide added, there was no significant difference in the attraction of female L. sericata, regardless of bait age. There was no general relationship between carrion bait age and the number of female L. sericata caught in different stages of ovarian development. The present data, therefore, suggest that L. sericata does not act exclusively as a pioneer species. Furthermore, this work suggests that, if used with sodium sulphide, the stage of carrion bait decomposition does not significantly modify carrion bait attractiveness.

The distribution and extent of parasitism of the apple ermine moth Yponomeuta malinellus Zeller by the polyembyronic encyrtid parasitoid Ageniaspis fuscicollis (Dalman) were examined in a three year field study and related to oviposition behaviour in the laboratory. Ageniaspis fuscicollis attacks egg batches of its host and kills the final instar larvae, which feed gregariously from within tents. Host population densities in the field were low, from 1.5 to 2.2 tents per 100 leaf clusters, and parasitism increased from 7.8% to 18% over the three year period. Parasitism was independent of host density at the whole tree scale, but at the individual tent scale, the probability of a tent containing parasitized host larvae increased and percent parasitism decreased with the number of host larvae per tent. Observations on the oviposition behaviour of A. fuscicollis in the laboratory revealed that parasitoids distributed their eggs randomly within host egg batches. On average, they spent almost two hours on an egg batch and laid 44% of their egg load of 132 eggs into the first egg batch visited, leading to a mean of 1.4 eggs laid per host egg through frequent self-superparasitism of hosts. The percentage of eggs receiving one or more ovipositions was independent of the size of an egg batch, contradicting our field observations of inverse density dependence. Factors that might account for the differences in rates of parasitism and attack distributions between laboratory and field data are discussed.

Responses of Stomoxys spp. to electrified targets (1 × 1 m) that differed in pattern and colour were investigated over a three month period at Rekomitjie Research Station, Zimbabwe. In the first experiment, a target baited with a blue and black cloth insert caught more flies (315 ± 117) than a target baited with blue cloth insert (202 ± 69). Next, a blue-cloth baited target caught more flies (491 ± 150) than a black-cloth baited target (164 ± 69) and a target containing a cloth with a black diamond on a blue background caught more flies (997 ± 326) than a target containing a cloth with a black square on a blue background (680 ± 125). Finally, a target fitted with a cloth consisting of a vertically oriented black stripe on a blue background caught almost three times as many flies (1366 ± 356) as a target fitted with a cloth consisting of a horizontally oriented black stripe on a blue background (545 ± 150). Hourly collections of Stomoxys spp. from a blue and black target, baited with and without carbon dioxide, indicated that daily activity was bimodal, with a small morning peak and a large late afternoon peak.

Variation in canopy arthropod abundances and community structure were evaluated in an old-growth (500-year-old) forest at the Wind River Canopy Crane Research Facility in southwestern Washington, USA. Arthropods were sampled at three canopy levels and two seasons in each of four tree species (Pseudotsuga menziesii, Tsuga heterophylla, Abies grandis, and Thuja plicata). The four tree species had distinguishable arthropod species compositions and community organization. Thuja plicata (Cupressaceae) had a particularly distinctive canopy fauna dominated by several mite taxa which did not occur on the other tree species (all Pinaceae). Pseudotsuga menziesii hosted a relatively diverse arthropod fauna with greatest richness of taxa and functional groups. Distinct arthropod assemblages were not observed among canopy levels and sampling dates, but these factors significantly influenced abundances of 63% of the arthropod taxa, either individually or interactively with other factors. These data indicate that forests managed for fewer tree species eliminate important components of arthropod diversity in Pacific Northwest forests and that sampling for biodiversity assessment also should represent season and canopy level.

Field surveys, manipulative field experiments and laboratory studies were employed to study the behaviour and development of a large coreid, Amorbus obscuricornis (Westwood), in response to changes in the architecture/foliar quality of Eucalyptus (Myrtaceae) hosts in Tasmania, Australia. Following tree decapitation and subsequent regrowth, A. obscuricornis nymphs were only associated with coppiced hosts. Eucalypts coppiced naturally by wild fire were found to carry significantly more nymphs than non-coppiced conspecific hosts. In contrast, adult A. obscuricornis were found on both coppiced and non-coppiced hosts. The foliar quality of coppiced hosts was superior to that of non-coppiced hosts; being softer, having a higher moisture content and a lower C/N ratio. Field collected fifth instar nymphs were heavier when collected from coppice vs. noncoppice; but in bagged shoot experiments second instar nymphs gained less weight on coppice than non-coppice. It is suggested that because coppice is softer the shoots may deteriorate (i.e. wilt) more quickly than non-coppice shoots. Through different exposure regimes, it was confirmed that first instar nymphs need only water to ecdyse, while feeding is initiated in the second instar. Differences in the nutritional requirements of first and second instar nymphs were reflected in their behaviour. First instar nymphs did not discriminate between conspecific hosts on the basis of whether they were coppiced or not, whereas second instar nymphs preferentially chose coppiced conspecific hosts. The findings of this work are discussed in the context of the plant vigour and resource regulation hypotheses.

Highly resistant and extremely resistant clones (R2 and R3) of Myzus persicae (Sulzer) exhibited a significantly lower mortality and developed a deleterious dark stomach deposit less frequently on sugarbeet than a susceptible (S) clone. After allowing equal populations of four resistant clones to develop together on sugarbeet for four weeks, approximately half of the aphids recovered were from the moderately resistant (R1) clone, suggesting that this clone had a significantly greater reproductive rate than the others. There was no significant difference in the propensity of any clone to produce alates on sugarbeet, although none of the clones produced very many. It is suggested that, even in the absence of insecticides on sugarbeet, resistant clones may become dominant due to their higher fecundity (R1 clones) and lower mortality (R2 and R3 clones) than susceptible clones.