No abstract

A technique for rapidly measuring non-lethal thermal tolerance traits in small insects and terrestrial arthropods of similar size is described. Single or multiple individuals are heated or cooled in an arena milled into a temperature-controlled aluminium block and their behaviour recorded continuously using a digital video camera. Data are collected retrospectively by playback of the stored images. To illustrate this technique measurement of six thermal tolerance traits using this method is described using first instar nymphs (body length ϭ 0.66 mm) of the aphid Myzus persicae . These traits are high and low temperatures at which individual aphids cease walking, high and low temperatures at which aphids move for the final time, the temperature at which aphids begin to recover from chill coma, and the temperature at which they begin to walk again. The method is validated by comparing the results of multiple low temperature assays. No significant differences are detected between assays. Potential applications, limitations and technical problems are discussed.

The predatory mirid Dicyphus hesperus Knight (Hemiptera: Miridae) is native to North America. The species has been used for the control of glasshouse whitefly on aubergine in the Netherlands, and is currently being evaluated for continued and wider release in Europe. Field and laboratory studies were conducted on a population collected from southern California, USA, to assess the cold tolerance and potential for outdoor establishment under prevailing northern European climates. The supercooling points (whole animal freezing temperatures) of nymphal and adult insects were around À208C. The lethal temperatures (LTemp 50 ) of non-diapausing nymphs and adults and diapausing adults were close to their respective freezing temperatures at À17.6, À17.6 and À19.28C. At 58C, the LTime 50 was 54, 101.7 and 117.5 days for fed nymphs, non-diapausing and diapausing adults respectively. When first instar nymphs were placed in the field in winter, starved samples died out after 70 days, but 5% of the fed nymphs survived until the end of winter (140 days) and developed to adult on return to the laboratory. After a similar 5-month field exposure, 50% of fed diapausing adults and 15% of fed non-diapausing adults were still alive at the end of winter, whereas starved diapausing adults died after 140 days. On return to the laboratory after 5 months in the field, both diapausing and non-diapausing adults mated and laid eggs, forming viable populations. Overall, the field and laboratory experiments indicate that this population of D. hesperus is able to enter diapause and that winter temperatures are not a barrier to establishment in northern Europe.

The outdoor establishment of non-native biocontrol agents released for inundative control of glasshouse pests is determined primarily by two factors: ecophysiological compatibility with local climate, particularly winter cold tolerance, and ability to locate and utilise wild prey. Observations on the number and diversity of acceptable wild prey as part of an assessment of establishment potential therefore overlap with more focused studies to determine host range. This study investigated two aspects of the interactions between biocontrol agents and non-target prey that are rarely considered in tests for establishment or host range: the role of different host plantprey associations in modifying the development and reproduction of biocontrol agents, and the longer term sustainability of such relationships beyond the single generation observed in most laboratory studies. Using the glasshouse whitefly (Trialeurodes vaporariorum) predator Macrolophus caliginosus Wagner (Hemiptera: Miridae) as a case study, the mirid was able to sustain viable populations over three generations on the related cabbage whitefly Aleyrodes proletella (Linnaeus) (Hemiptera: Aleyrodidae) and the aphid Myzus persicae (Sulzer) (Hemiptera: Aphididae), including when these prey were feeding on different host plants (Chinese cabbage, cabbage and Brussels sprout). However, the rate of development, fecundity and mortality of the predator varied between the different prey and host plant combinations, and in all cases differed than when feeding on its glasshouse prey T. vaporariorum reared on tobacco (Nicotiana tabacum). The results are discussed in the light of the current debate on methods for conducting host range testing as part of an environmental risk assessment.