The cabbage aphid, Brevicoryne brassicae, has developed a chemical defence system that exploits and mimics that of its host plants, involving sequestration of the major plant secondary metabolites (glucosinolates). Like its host plants, the aphid produces a myrosinase (b-thioglucoside glucohydrolase) to catalyse the hydrolysis of glucosinolates, yielding biologically active products. Here, we demonstrate that aphid myrosinase expression in head/thoracic muscle starts during embryonic development and protein levels continue to accumulate after the nymphs are born. However, aphids are entirely dependent on the host plant for the glucosinolate substrate, which they store in the haemolymph. Uptake of a glucosinolate (sinigrin) was investigated when aphids fed on plants or an in vitro system and followed a different developmental pattern in winged and wingless aphid morphs. In nymphs of the wingless aphid morph, glucosinolate level continued to increase throughout the development to the adult stage, but the quantity in nymphs of the winged form peaked before eclosion (at day 7) and subsequently declined. Winged aphids excreted significantly higher amounts of glucosinolate in the honeydew when compared with wingless aphids, suggesting regulated transport across the gut. The higher level of sinigrin in wingless aphids had a significant negative impact on survival of a ladybird predator. Larvae of Adalia bipunctata were unable to survive when fed adult wingless aphids from a 1% sinigrin diet, but survived successfully when fed aphids from a glucosinolate-free diet (wingless or winged), or winged aphids from 1% sinigrin. The apparent lack of an effective chemical defence system in adult winged aphids possibly reflects their energetic investment in flight as an alternative predator avoidance mechanism.

The hypothesis that plants supplied with organic fertilizers are better defended against insect herbivores than those supplied with synthetic fertilizers was tested over two field seasons. Organic and synthetic fertilizer treatments at two nitrogen concentrations were supplied to Brassica plants, and their effects on the abundance of herbivore species and plant chemistry were assessed. The organic treatments also differed in fertilizer type: a green manure was used for the low-nitrogen treatment, while the highnitrogen treatment contained green and animal manures. Two aphid species showed different responses to fertilizers: the Brassica specialist Brevicoryne brassicae was more abundant on organically fertilized plants, while the generalist Myzus persicae had higher populations on synthetically fertilized plants. The diamondback moth Plutella xylostella (a crucifer specialist) was more abundant on synthetically fertilized plants and preferred to oviposit on these plants. Glucosinolate concentrations were up to three times greater on plants grown in the organic treatments, while foliar nitrogen was maximized on plants under the higher of the synthetic fertilizer treatments. The varying response of herbivore species to these strong differences in plant chemistry demonstrates that hypotheses on defence in organically grown crops have over-simplified the response of phytophagous insects.

Brassica nigra plants, characterized by high levels of sinigrin, and artificial aphid diets to which sinigrin was selectively added were used to rear the crucifer specialist, Brevicoryne brassicae. Aphids were provided as a food source to two species of polyphagous ladybird, Adalia bipunctata and Coccinella septempunctata. First instar A. bipunctata were unable to survive when fed with B. brassicae reared on B. nigra or diets containing 0.2% sinigrin, but when fed with aphids reared on diets containing 0% sinigrin, survival rates were high. By contrast, first instar C. septempunctata were able to survive when fed with aphids reared on B. nigra or artificial diets containing up to 1% sinigrin. However, the presence of sinigrin in the aphid diet decreased larval growth and increased the time necessary for larvae to reach second instar for this species of ladybird. These results indicate that the presence of sinigrin in the diet of B. brassicae makes this aphid unsuitable as a food source for A. bipunctata but not for C. septempunctata, although for this ladybird species, there appear to be costs associated with feeding on aphids that contain this secondary metabolite.

1 The rosy apple aphid, Dysaphis plantaginea , is the most serious pest of apple in Europe and, although conventionally controlled by insecticides, alternative management measures are being sought. Colonies of D. plantaginea are commonly attended by ants, yet the effects of this relationship have received little attention. 2 An ant exclusion study was conducted in two distant orchards within the U.K. At both sites, ants were excluded from a subset of D. plantaginea infested trees at the beginning of the season and populations were monitored. The number of natural enemies observed on trees was also recorded and, before harvest, the percentage of apples damaged by D. plantaginea calculated. 3 Overall, the exclusion of ants reduced the growth and eventual size of D. plantaginea populations. On trees accessed by ants, greater numbers of natural enemies were recorded, presumably because aphid populations were often greater on such trees. However, this increased natural enemy presence was diluted by the larger aphid populations such that individual aphids on ant-attended trees were subjected to a lower natural enemy pressure compared with those on ant-excluded trees. 4 At harvest, apple trees that had been accessed by ants bore a greater proportion of apples damaged by D. plantaginea . There were also differences in cultivar susceptibility to D. plantaginea damage. 5 The present study highlights the importance of the ant -D. plantaginea relationship and it ia suggested that ant manipulation, whether physically or by semiochemicals that disrupt the relationship, should be considered as a more prominent component in the development of future integrated pest management strategies.

Wingbeat frequency in insects is an important variable in aerodynamic and energetic analyses of insect flight and often is studied on a family-or species-level basis. Meta-analyses of these studies report order-level patterns suggesting that flight strategy is moderately well conserved phylogenetically. Studies incorporated into these meta-analyses, however, use variable methodologies across different temperatures, which may confound results and phylogenetic patterns. In the present study, a high-speed camera is used to measure wingbeat frequency in a wide variety of species (n = 102) under controlled conditions aiming (i) to determine the validity of previous meta-analyses showing phylogenetic clustering of flight strategy and (ii) to identify new evolutionary patterns between wingbeat frequency, body mass, wing area, wing length and wing loading at the order level. All flight-associated morphometrics significantly affect wingbeat frequency. Linear models show that wing area explains the most amount of variation in wingbeat frequency (r 2 = 0.59, P ≤ 0.001), whereas body mass explains the least (r 2 = 0.09, P ≤ 0.01). A multiple regression model incorporating both body mass and wing area is the best overall predictor of wingbeat frequency (r 2 = 0.84, P ≤ 0.001). Order-level phylogenetic patterns across relationships are consistent with previous studies. Thus, the present study provides experimental validation of previous meta-analyses and provides new insights into phylogenetically conserved flight strategies across insect orders.

Cruciferous plants (Brassicaceae) are characterized by the accumulation of a group of secondary metabolites known as glucosinolates that, following attack by pathogens or herbivores, may be hydrolyzed to one of a number of products including isothiocyanates and nitriles. Despite the range of hydrolysis products that may be produced, the toxicity of glucosinolates to pathogens and herbivores may be explained largely by the production of isothiocyanates. Isothiocyanates are also known to provide an indirect defense by acting as host finding cues for parasitoids of insect herbivores that attack crucifers. It has been speculated that nitriles may provide a similar indirect defense. Here, we investigate the olfactory perception and orientation behavior of the aphid parasitoid Diaeretiella rapae, to a range of alkenylglucosinolate hydrolysis products, including isothiocyanates, nitriles, and epithionitriles. Electroantennogram responses indicated peripheral odor perception in D. rapae females to all 3-butenylglucosinolate hydrolysis products tested. By contrast, of the 2-propenylglucosinolate hydrolysis products tested, only the isothiocyanate elicited significant responses. Despite showing peripheral olfactory detection of a range of 3-butenylglucosinolate hydrolysis products, naïve females oriented only to the isothiocyanate. Similarly, parasitoids oriented to 3-isothiocyanatoprop-1-ene, but not to the corresponding nitrile or epithionitrile. However, by rearing D. rapae either on Brassica nigra, characterized by the accumulation of 2-propenylglucosinolate, or Brassica rapa var rapifera, characterized by the accumulation of 3-butenylglucosinolate, altered the innate response of parasitoids to 3-isothiocyanatoprop-1-ene and 4-isothiocyanatobut-1-ene. These results are discussed in relation to the defensive roles of glucosinolate hydrolysis products and the influence of the host plant on aphid parasitoid behavior.

DL-b-Aminobutyric acid (BABA) is a nonprotein amino acid that can enhance defences in a variety of plants against a wide range of pathogens. BABA can also reduce infestation by phytopathogenic nematodes and has recently been shown to suppress the growth of aphids feeding on legumes. This investigation examined the effect of applying BABA as a root drench to a range of Brassicaceae, including Arabidopsis thaliana, on the performance of two species of aphid (Myzus persicae and Brevicoryne brassicae) and the larvae of two species of Lepidoptera (Trichoplusia ni and Plutella xylostella). Application of BABA reduced the performance of all four insect species, and inhibition of insects occurred on all the plants tested. The results illustrate that BABAinduced resistance (BABA-IR) can affect generalist and specialist insect herbivores and inhibit insects feeding with mandibulate as well as sap-feeding mouthparts. The BABA-induced suppression of B. brassicae and P. xylostella feeding on A. thaliana provides a means to further examine the mechanisms of BABA-IR to insects using this model plant.

Vine weevil, Otiorhynchus sulcatus F. (Coleoptera: Curculionidae), is an economically 20 important pest species in many soft-fruit and ornamental crops. Economic losses arise from 21 damage to the roots, caused by larvae, and to the leaves, caused by adults. As adults are nocturnal and larvae feed below ground, infestations can initially be missed, and controls 23 may, as a result, be applied too late. In the absence of a vine weevil sex or aggregation 24 pheromone being identified, the development of an effective semiochemical lure for better 25 management of this pest is likely to focus on host-plant volatiles. Here, we investigate the 26 electrophysiological and behavioral responses of adult vine weevils to volatile organic 27 compounds (VOCs) originating from their preferred host plant Euonymus fortunei, and 28 synthetic VOCs associated with this host when presented individually or as blends. 29 Consistent electroantennographic responses were observed to a range of generalist VOCs. 30 Behavioral responses to VOCs, when presented individually, were found to be influenced by 31 the concentration of the compound to which the weevils were exposed. Vine weevil adults 32 showed directional movement towards a mixture of seven plant volatiles (methyl salicylate, 33 1-octen-3-ol, (E)-2-hexenol, (Z)-3-hexenol, 1-hexanol, (E)-2-pentenol, and linalool) even 34 though either no response or negative responses were recorded to each of these compounds 35 when presented individually. Similarly, vine weevils showed directional movement towards a 36 1:1 ratio mixture of (Z)-2-pentenol and methyl eugenol. Results presented here point to the 37 importance of blends of generalist compounds and concentrations of VOCs in the 38 optimization of a lure.