The aphid Rhopalosiphum padi (L.) coexists with the leafhopper Psammotettix alienus (Dahlbom) in the same cereal crops. However, dense populations of the aphid were never observed to be associated with dense populations of the leafhopper. This laboratory study focuses on the effect of the aphid at various densities on the development and reproductive biology of the leafhopper and constitutes a preliminary test to understand the interactions between these insects in the field. Independently of food quantity, an increase in aphid numbers caused a lengthening of development duration and increased mortality of leafhopper nymphs. In the absence of aphids, leafhopper nymphs preferred to feed on the lower part of the plant. In the presence of aphids, the leafhoppers moved towards the upper part of the plant. An increase in aphid numbers had no significant influence on the longevity of leafhopper females, although the daily fecundity decreased significantly. These data demonstrate the negative effect of R. padi on the development and fecundity of P. alienus and corroborated the field observations. Because food quantity was not the limiting factor, further experiments are underway to elucidate the factors modifying leafhopper biology. Such factors could be used to manipulate leafhopper populations.

The metabolic pathways of ingested ecdysteroids have been investigated in three insect species, the aphid Myzus persicae and two Lepidoptera, Plodia interpunctella and Ostrinia nubilalis. M. persicae produces mainly a 22-glucoside conjugate, whereas P. interpunctella eliminates a mixture of 20E and its 3-oxo and 3-epi derivatives, both in free form and as conjugates with various fatty acids. O. nubilalis only produces fatty acyl ester conjugates. These data point out the great diversity of detoxification mechanisms used by phytophagous insects in order to overcome the potential harmful effects of ecdysteroids present in their food.

Transgenesis developed in the last 20 years offers new possibilities for crop protection. The transgenic process, however, requires the use of marker fusion genes to select and visualize the transformed tissues. Although the expression products of these marker genes are stably expressed in crops, little attention has been given to assess the eventual risks of these recombinant proteins on phytophage populations. Three independent transgenic potato ( Solanum tuberosum ) clones from the cultivar Désirée (DG5, DG18, and DG20) carrying the commonly used nptII-gus gene construct and exhibiting different β -glucuronidase activity (0.843 ± 0.011, 0.576 ± 0.096, and 0.002 ± 0.000 pmol min − 1 .mg − 1 , respectively) were evaluated to determine the impact of the encoded proteins on the behaviour, development, reproduction, and demography of the peach-potato aphid, Myzus persicae , under laboratory-controlled light and temperature. Our results revealed that the transgenic event can alter aphid physiology or behaviour. Experiments showed a probiotic effect of one transgenic line, the DG5, resulting in reduced prereproductive period and mortality, and enhanced daily fecundity, which was expressed in a greater population growth potential (r m = 0.205 vs. r m = 0.174 of the control). In contrast, aphids fed with the DG18 line exhibited reduced adult survival and reproductive period but no alteration of their demographic parameters (r m = 0.176). Finally, no physiological alteration was induced in aphids fed on a DG20 diet (r m = 0.170). Behavioural experiments conducted in a 4-choice olfactometer demonstrated that insects were significantly more attracted by the odour of transgenic DG18 potato plant than that of Désirée non-transformed plant, spending twice as much time in the DG18 plant odour. The two other transformed clones (DG5 and DG20) were as attractive as the non-transformed cultivar. It is concluded that the β -glucuronidase expression in potato plants might be responsible for the probiotic effect measured on the feeding aphids, whereas alteration of the foliage odour would result from a pleiotropic effect.

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