▪ Abstract Interest in trap cropping, a traditional tool of pest management, has increased considerably in recent years. In this review we propose a broader definition of trap cropping that encompasses the inherent characteristics of the trap crop plants themselves as well as the strategies associated with their deployment. Inherent characteristics of a trap crop may include not only natural differential attractiveness for oviposition and feeding, but also other attributes that enable the trap crop plants to serve as a sink for insects or the pathogens they vector. Successful deployment of trap crops within a landscape depends on the inherent characteristics of the trap crop and the higher value crop, the spatial and temporal characteristics of each, the behavior and movement patterns of insect pests, and the agronomic and economic requirements of the production system. Thus, trap cropping is more knowledge-intensive than many other forms of pest management. We review recent references on trap cropping, classify them according to their modalities and level of implementation, and provide a synthesis of the factors that influence the success of trap cropping. Last, we provide a list of recommendations and guidelines that should prove helpful in moving trap cropping forward to its full potential.

Despite the prominent and worldwide use of Bacillus thuringiensis (Bt) insecticidal toxins in agriculture, knowledge of the mechanism by which they kill pests remains incomplete. Here we report genetic mapping of a membrane transporter (ABCC2) to a locus controlling Bt Cry1Ac toxin resistance in two lepidopterans, implying that this protein plays a critical role in Bt function.

Summary: 1. Plants face threats from a variety of herbivorous insects and can use induced responses to defend themselves against these attackers. Induced responses are mediated by signal transduction involving phytohormones, such as jasmonic acid (JA) and salicylic acid (SA). Cross‐talk between signal transduction pathways triggered by attackers with contrasting feeding styles allows plants to fine‐tune defences. A central question in this emerging field is to understand how responses to single attackers interfere with responses to other attackers, especially by integratively addressing molecular and ecological aspects.2. We examined the plant‐mediated interactions between the leaf‐chewing Pieris brassicae and the phloem‐sucking Brevicoryne brassicae, and their respective parasitoids Cotesia glomerata and Diaeretiella rapae, when feeding simultaneously, sequentially or in isolation on the brassicaceous ecological model plant Brassica oleracea. We analysed the underlying defence mechanisms in the plant. Levels of the phytohormones JA and SA transcriptional responses of a number of selected defence‐related genes and secondary plant compounds were quantified at different time points during the single and multiple infestations.3. The caterpillars developed faster and reached a larger body mass on plants previously attacked by aphids. Aphids initially developed faster on plants with caterpillars, although the moment of moulting to adults was independent of the presence of caterpillars. Both parasitoid species performed better under multiple‐infestation scenarios than in single‐herbivore situations.4. On plants attacked by aphids, the JA levels were tenfold lower than on undamaged plants or plants with caterpillars. Additionally, the low transcript levels of LOX and MYC, genes coding for a JA biosynthesis‐related enzyme and a transcription factor, respectively, in aphid‐infested plants, suggest that the facilitation of the caterpillar performance was mediated by interference in signal transduction. Levels of carbon and nitrogen and secondary plant compounds (glucosinolates) did not differ significantly between treatments, suggesting that these compounds did not mediate the facilitation.5. Our data show that the leaf chewer and phloem feeder asymmetrically interact not via competition as would be expected from interspecific herbivores but instead via facilitation; the phloem feeder attenuated JA‐related plant defences, thus facilitating the growth and development of the leaf chewers. In linear bitrophic systems, interactions between JA and SA signalling pathways have been proposed to allow plants to fine‐tune their defences, but if facilitation frequently occurs in interspecific interguild interactions among herbivores this may represent an important constraint for plant defences. Such a constraint might be reduced if, as in our model system, parasitoids also benefit from interactions between interguild hosts and nonhosts, but parasitoids are rarely considered in model molecular systems to assess the impact of herbivore‐induced plant defences.

Glucosinolates are plant secondary metabolites used in plant defense. For insects specialized on Brassicaceae, such as the diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae), glucosinolates act as “fingerprints” that are essential in host plant recognition. Some plants in the genus Barbarea (Brassicaceae) contain, besides glucosinolates, saponins that act as feeding deterrents for P. xylostella larvae, preventing their survival on the plant. Two-choice oviposition tests were conducted to study the preference of P. xylostella among Barbarea leaves of different size within the same plant. P. xylostella laid more eggs per leaf area on younger leaves compared to older ones. Higher concentrations of glucosinolates and saponins were found in younger leaves than in older ones. In 4-week-old plants, saponins were present in true leaves, while cotyledons contained little or no saponins. When analyzing the whole foliage of the plant, the content of glucosinolates and saponins also varied significantly in comparisons among plants that were 4, 8, and 12 weeks old. In Barbarea plants and leaves of different ages, there was a positive correlation between glucosinolate and saponin levels. This research shows that, in Barbarea plants, ontogenetical changes in glucosinolate and saponin content affect both attraction and resistance to P. xylostella. Co-occurrence of a high content of glucosinolates and saponins in the Barbarea leaves that are most valuable for the plant, but are also the most attractive to P. xylostella, provides protection against this specialist herbivore, which oviposition behavior on Barbarea seems to be an evolutionary mistake.