Antioxidant, insecticidal, antifeedant, and repellent activities of oregano (Origanum vulgare).

This study aimed to assess the antioxidant capacity, the insecticidal, feeding deterrence, repellent effects against Tribolium confusum of the essential oil (EO) and the organic extracts (ME) of Origanum vulgare. The chemical composition of the EO revealed the presence thirty-nine components dominated by carvacrol (81%). With respect to the EO, the ME acted as a potent free radical scavenger with IC50 values of 0.127 and 0.058 mg/mL, respectively. The EO exhibited the most significant toxicity compared to the ME with a mortality of 62 and 20% at 0.08 µL/insect after 24h whereas the EO expressed the highest repellency compared to the ME with a PR of 70 and 38% after 24h. As for feeding deterrence, both samples influenced all nutritional indexes. The findings found in this work might help in the promotion of oregano as natural antioxidant, antifeedant, repellent and insecticide as an alternative to conventional harmful ones.

Chemical profiling and bioactivities of essential oils from Thymus capitatus and Origanum compactum against Tribolium castaneum.

The use of essential oils has emerged as an ecofriendly solution for controlling different pests, particularly insects of stored products. Essential oils (EOs) from Thymus capitatus (TC) and Origanum compactum (OC) have received less attention for these bioactivities. Therefore, our study aimed to assess the repellent, antifeedant and contact toxicity of their EOs against a major stored product pest Tribolium castaneum. Besides, GC-MS was also carried out to determine the compounds responsible for the observed bioactivities. Regarding contact toxicity, LC50 values were 0.58 and 0.35 µL/cm2 for TC and OC after 24 h of exposure, respectively. For the repellent effect, the percentage of repellency (PR) was variable across different concentrations and exposure durations. TC exhibited the best PR (98%) after 3 h of exposure at 0.031 µL/cm2. For prolonged repulsive effect (24 h), TC sustained its repulsive efficacy with a PR of 90% at 0.062 µL/cm2 followed by OC with a PR of 88% at 0.125 µL/cm2. As for the antifeedant effect, both EOs had a significant impact on nutritional indexes, especially the feeding deterrent index and relative consumption rate. OC displayed a notable effect, causing 59% of feeding deterrence at 1.92 µL/pellet. These multifaced effects can be explained by the high content of carvacrol in both EOs (OC: 90% and TC: 78%). These multifaced effects demonstrated through different exposure routes and bioassays promote the use of T. capitatus and O. compactum EOs as a sustainable management strategy to control T. castaneum.

Phenolic secondary metabolites from Acorus calamus (Acorales: Acoraceae) rhizomes: the feeding deterrents for Spodoptera litura (Lepidoptera: Noctuidae).

Spodoptera litura Fabricius (Lepidoptera: Noctuidae) is one of the most destructive pests of various crops cultivated in Thailand. Spodoptera litura larvae, at early stages, attack the leaves and feed on every part of infested crops in later stages. Acorus calamus essential oil contains toxic asarones, which are generalistic cytotoxic compounds. However, the present study is the first attempt to look at safer metabolites from the rhizomes that could deter insect feeding. The objective was to use such compounds as safer residues on crops that would prevent the feeding of herbivorous lepidopterans. Accordingly, phenolic metabolites were isolated and evaluated to establish the feeding deterrence against polyphagous S. litura larvae. Methanol extract of A. calamus, chrysin, and 4-hydroxy acetophenone compounds were the most effective feeding deterrents with FD50 of 87.18, 10.33, and 70.77 µg/cm2, respectively, after 4 h of feeding on treated kale leaves in a no-choice leaf disc assay. Chrysin also reduced carboxylesterase activities (1.37-fold), whereas A. calamus methanol extract reduced glutathione-S-transferase activities (1.44-fold). Some larvae were also seen dead if they consumed the treated kale leaves. Feeding deterrent activity in the methanol extract of A. calamus was due to chrysin and 4-hydroxy acetophenone. The large-scale utilization of such compounds could help develop feeding deterrent strategies in the integrated pest management of lepidopterans.

Dhurrin: A naturally occurring phytochemical as a weapon against insect herbivores.

Dhurrin, a cyanogenic glucoside, is a plant defensive chemical synthesized from aliphatic amino acids and consists of ß-d-glucopyranose linked to α-hydroxy nitrile. It is catabolized by the consecutive action of hydroxynitrilase and ß-glucosidase to release hydrogen cyanide on tissue disruption during herbivory. These phytoanticipins are widely distributed across various monocot and dicot plants such as Sorghum, Macadamia, Ostrya sp., and many other plant species with ornamental, pharmaceutical, medicinal, and food value. Although repellent properties of dhurrin against herbivores are often reported, less is known about its distribution, metabolism, mode of action against insects, and application for pest control. Herein, we highlight recent updates on dhurrin distribution, biosynthesis, and catabolism along with the cyanide detoxification pathway. Additionally, this article focuses on biological activities of dhurrin against various herbivores and opportunities to explore the utilization of dhurrin as a natural pest control agent and a substitute for chemically synthesized pesticides.

Natural and Synthetic Pyrethrins Act as Feeding Deterrents against the Black Blowfly, Phormia regina (Meigen).

Pyrethrum is a botanical insecticide derived from pyrethrum flowers. Feeding deterrence caused by pyrethrum has been reported in several sucking insects; however, there is no account of the cause of deterrence-whether from a single component or the combination of six active ingredients, called pyrethrins. We determined the feeding deterrence of natural pyrethrins, their two main components (pyrethrins I and II), and pyrethroid insecticides on the blowfly, Phormia regina. In a dual-choice feeding assay that minimized tarsal contact with food sources but allowed feeding through proboscises, natural pyrethrins, synthetic pyrethrins I/II, and allethrin were observed to induce deterrence at a concentration 16 times lower than the lowest concentration at which the knockdown rate increased. Feeding bouts were interrupted by intensive grooming of the proboscis at the deterring concentration, but no such grooming was observed to occur while feeding on the unpalatable tastants-NaCl, quinine, and tartaric acid. The underlying mode of action for the feeding deterrence of pyrethrins at sub-lethal concentrations probably occurs on the fly oral gustatory system, while differing from that of unpalatable tastants. The potent feeding deterrence of pyrethrins may provide effective protection for pyrethrum plants by rapidly deterring insects from feeding, before insecticidal activities occur.

Insecticidal and Feeding Deterrent Effects of Kaempferia galanga L. and Amomum subulatum on Pieris rapae L. Larva.

<b>Background and Objective:</b> <i>Pieris rapae</i> L., is one of the most widespread and destructive pests of cruciferous plants. At present, synthetic chemical insecticide is still the main approach to control this pest despite several disadvantages to human health and the wildlife environment as well as biological resistance. To search for plants having insecticidal activity, the biological effects of two medicinal plants <i>Kaempferia galanga</i> L. and <i>Amomum subulatum </i>on <i>Pieris rapae</i> L., were investigated. <b>Materials and Methods:</b> The methanol extracts of dry rhizomes and fruits of <i>Kaempferia galanga</i> L. and <i>Amomum subulatum </i>were used to determine the mortality, feeding and oviposition deterrence of larvae and adult of <i>Pieris rapae</i> L. <b>Results:</b> <i>Kaempferia galanga</i> L. and <i>Amomum subulatum</i> exhibited insecticidal activity against <i>Pieris rapae</i> L., with LC₅₀ values of 2.11 and 11.80% (w/v), respectively. In the antifeedant test, <i>Kaempferia galanga</i> L., extract showed no significant difference with the control at the low concentration (0.5 and 1%). Whereas, with a concentration of 0.5%, <i>Amomum subulatum</i> extract demonstrated a high antifeedant effect on <i>Pieris rapae</i> L., larvae. In addition, plants treated with these two extracts reduced eggs laid by <i>Pieris rapae</i> L., in field conditions showing the oviposition deterrent properties. <b>Conclusion:</b> These results indicated that <i>Kaempferia galanga</i> L. and <i>Amomum subulatum </i>extracts have insecticidal substances against <i>Pieris rapae </i>L., which can be used for developing effective pesticides or/and oviposition deterrents for integrated pest management.

Antifeedant Effect of Some Medicinal Plant Extracts Against Rice Weevil.

BACKGROUND AND OBJECTIVE: At present, insecticides with raw materials of active compounds from plants have become a strategic alternative, because they are easily obtained and produced. In an attempt to find natural and cheaper methods for the control of rice weevil (Sitophilus oryzae L.), some useless waste of local medicinal plant extracts was evaluated. This study aimed to evaluate the antifeedant effect of various medicinal plant extracts on rice weevil (Sitophilus oryzae L.). MATERIALS AND METHODS: The experimental study using a completely randomized design of two factors, i.e., source of the extract in 7 types of medicinal plant waste and the exposure time of extracts in 0, 1, 2 and 3 h. The antifeedant effects were evaluated after 3 weeks by measuring feed consumption (FC), feeding deterrent index (FDI) and rice weevils' mortality. Data were analyzed using variance analysis. RESULTS: The statistical analysis showed that the differences in exposure time contributed significant influence (α<0.05) on FC, FDI and mortality. The lowest FC occurred at the 3 h exposure treatment, i.e. on the extract of Amomum cardamom plant, while the highest FC was found in the treatment of Curcuma mangga plant extract. The values of FDI and mortality at the 3 h extract exposure were 31.53-87.16% and 42.4-64%, respectively with the highest value in the treatment of A. cardamomum. CONCLUSION: At last, these findings inform peoples that the waste of medicinal plants, especially cardamom is possible to be developed as botanical insecticides for rice weevils.

Comparison of Phenylacetates with Benzoates and Phenylpropanoates as Antifeedants for the Pine Weevil, Hylobius abietis.

This study concludes an extensive investigation of antifeedants for the pine weevil, Hylobius abietis (Coleoptera: Curculionidae), an economically important pest of planted conifer seedlings. Building on the previously reported antifeedant effects of benzoates and phenylpropanoids (aromatic compounds with one- or three-carbon-atom substituents on the benzene ring), we here report the antifeedant effects of compounds with two-carbon-atom side chains (i.e., phenylacetates). We also present new results; the best antifeedants from the benzoate class were tested at 10-fold lower concentrations in order to find the optimal antifeedants. Generally, for all three compound classes, efficient antifeedants were found to have one or two methyl, chloro, or methoxy substituents on the aromatic ring. For monosubstituted phenylpropanoids, the substituent preferably should be in the para-position. In the search for synergistic antifeedant effects among the three compound classes, combinations of compounds from the three classes were tested in binary and ternary mixtures.

Mini review: Gustatory reception of chemicals affecting host feeding in aedine mosquitoes.

Mosquitoes vector dangerous human diseases during blood feeding. Gustatory (taste) receptor neurons in the mosquito provide important chemical information including the nature and suitability of a potential host. Here we discuss the behavior, neurophysiology and molecular mechanisms associated with feeding in aedine mosquitoes, important vectors of emerging diseases including Zika fever, chikungunya and dengue fever. We describe how interactions between feeding stimulation and deterrency at the peripheral neural receptor level provide input to higher order neural processing centers affecting decisions to feed. A better understanding of gustatory mechanisms involved in the female's decision to bite will provide the framework for novel strategies aimed at preventing the spread of vector-borne disease.

Chemical Constituents of Supercritical Extracts from Alpinia officinarum and the Feeding Deterrent Activity against Tribolium castaneum.

Alpinia officinarum has been confirmed to possess bioactivities against some pests. In this work, a sample was obtained from A. officinarum rhizomes by supercritical fluid CO2 extraction (SFE). According to GC-MS analysis, the main chemical components for SFE-sample included benzylacetone (26.77%), 1,7-diphenyl-5-hydroxy-3-heptanone (17.78%), guaiacylacetone (10.03%) and benzenepropanal (7.42%). The essential oil of A. officinarum rhizomes (LD50 = 20.71 µg/adult) exhibited more contact toxicity than SFE extract (LD50 = 82.72 µg/adult) against Tribolium castaneum. From SFE extracts, one new compound, 1-phenyl-4-(16,17-dimethyl-9,13-octadiene)-5-isopentenyl-7-(4"-methoxyl-3"-hydroxyl-phenyl)-3-heptanone (3), together with five known compounds identified as 5-hydroxy-1,7-diphenyl-3-heptanone (1), 1,7-diphenyl-4-hepten-3-one (2), galangin (4), galangin-3-methyl ether (5) and pinocembrin (6), were isolated and their feeding deterrent activities against T. castaneum adults were assessed. It was found that compounds 1-6 had feeding deterrent activities against T. castaneum with feeding deterrent indices of 18.21%, 18.94%, 19.79%, 26.99%, 20.34%, and 35.81%, respectively, at the concentration of 1500 ppm. Hence, the essential oil and SFE extracts/compounds of A. officinarum rhizomes represent promising alternatives in the control of T. castaneum adults.

Leucokinin mimetic elicits aversive behavior in mosquito Aedes aegypti (L.) and inhibits the sugar taste neuron.

Insect kinins (leucokinins) are multifunctional peptides acting as neurohormones and neurotransmitters. In females of the mosquito vector Aedes aegypti (L.), aedeskinins are known to stimulate fluid secretion from the renal organs (Malpighian tubules) and hindgut contractions by activating a G protein-coupled kinin receptor designated "Aedae-KR." We used protease-resistant kinin analogs 1728, 1729, and 1460 to evaluate their effects on sucrose perception and feeding behavior. In no-choice feeding bioassays (capillary feeder and plate assays), the analog 1728, which contains α-amino isobutyric acid, inhibited females from feeding on sucrose. It further induced quick fly-away or walk-away behavior following contact with the tarsi and the mouthparts. Electrophysiological recordings from single long labellar sensilla of the proboscis demonstrated that mixing the analog 1728 at 1 mM with sucrose almost completely inhibited the detection of sucrose. Aedae-KR was immunolocalized in contact chemosensory neurons in prothoracic tarsi and in sensory neurons and accessory cells of long labellar sensilla in the distal labellum. Silencing Aedae-KR by RNAi significantly reduced gene expression and eliminated the feeding-aversion behavior resulting from contact with the analog 1728, thus directly implicating the Aedae-KR in the aversion response. To our knowledge, this is the first report that kinin analogs modulate sucrose perception in any insect. The aversion to feeding elicited by analog 1728 suggests that synthetic molecules targeting the mosquito Aedae-KR in the labellum and tarsi should be investigated for the potential to discover novel feeding deterrents of mosquito vectors.

Feeding Deterrent and Genotoxicity Analysis of a novel Phytopesticide by using Comet Assay against Helicoverpa armigera (HÜbner) (Lepidoptera: Noctuidae)

Newly developed Phytopesticidal formulations from pongam and neem oils were evaluated for their feeding deterrent activity using leaf disc choice and no-choice methods, and genotoxic study using comet assay against Helicoverpa armigera at different concentrations of 5, 10, 15, and 20 ppm. Among various phytopesticidal formulations, neem and pongam oils at 1:1 ratio, called PONNEEM showed significant feeding deterrent activity against H. armigera at 20 ppm concentration and wasgenotoxic to H. armigera (P>0.001). The comet parameters, namely tail moment (arbitrary units), tail length (µm) and tail DNA (%) were observed at all the concentrations of PONNEEM. Statistically significant changes in all the comet parameters of H. armigera were observed at 20 ppm (P<0.001). Feeding deterrent and genotoxicity effect of PONNEEM could be applied as phytopesticide for controlling the lepidopteran insect pests.

Feeding deterrent and growth inhibitory activities of PONNEEM, a newly developed phytopesticidal formulation against Helicoverpa armigera (Hubner).

OBJECTIVE: To assess the feeding deterrent, growth inhibitory and egg hatchability effects of PONNEEM on Helicoverpa armigera (H. armigera). METHODS: Five oil formulations were prepared at different ratios to assess the feeding deterrent, growth inhibitory and egg hatchability effects on H. armigera. RESULTS: Invariably all the newly formulated phytopesticidal oil formulations showed the feeding deterrent and growth inhibitory activities against H. armigera. The maximum feeding deterrent activity of 88.44% was observed at 15 µL/L concentration of PONNEEM followed by formulation A (74.54%). PONNEEM was found to be effective in growth inhibitory activities and egg hatchability at 10 µL/L concentration. It exhibited statistically significant feeding deterrent activity and growth inhibitory activity compared with all the other treatments. CONCLUSIONS: PONNEEM was found to be effective phytopesticidal formulation to control the larval stage of H. armigera. This is the first report for the feeding deterrent activity of PONNEEM against H. armigera. This newly formulated phytopesticide was patented in India.

Will chemical defenses become more effective against specialist herbivores under elevated CO2?

Elevated atmospheric CO2 is known to affect plant-insect herbivore interactions. Elevated CO2 causes leaf nitrogen to decrease, the ostensible cause of herbivore compensatory feeding. CO2 may also affect herbivore consumption by altering chemical defenses via changes in plant hormones. We considered the effects of elevated CO2, in conjunction with soil fertility and damage (simulated herbivory), on glucosinolate concentrations of mustard (Brassica nigra) and collard (B. oleracea var. acephala) and the effects of leaf nitrogen and glucosinolate groups on specialist Pieris rapae consumption. Elevated CO2 affected B. oleracea but not B. nigra glucosinolates; responses to soil fertility and damage were also species-specific. Soil fertility and damage also affected B. oleracea glucosinolates differently under elevated CO2. Glucosinolates did not affect P. rapae consumption at either CO2 concentration in B. nigra, but had CO2-specific effects on consumption in B. oleracea. At ambient CO2, leaf nitrogen had strong effects on glucosinolate concentrations and P. rapae consumption but only gluconasturtiin was a feeding stimulant. At elevated CO2, direct effects of leaf nitrogen were weaker, but glucosinolates had stronger effects on consumption. Gluconasturtiin and aliphatic glucosinolates were feeding stimulants and indole glucosinolates were feeding deterrents. These results do not support the compensatory feeding hypothesis as the sole driver of changes in P. rapae consumption under elevated CO2. Support for hormone-mediated CO2 response (HMCR) was mixed; it explained few treatment effects on constitutive or induced glucosinolates, but did explain patterns in SEMs. Further, the novel feeding deterrent effect of indole glucosinolates under elevated CO2 in B. oleracae underscores the importance of defensive chemistry in CO2 response. We speculate that P. rapae indole glucosinolate detoxification mechanisms may have been overwhelmed under elevated CO2 forcing slowed consumption. Specialists may have to contend with hosts with poorer nutritional quality and more effective chemical defenses under elevated CO2.

Behavioural responses of Frankliniella occidentalis Pergande larvae to methyl jasmonate and cis-jasmone.

The larval stages of Frankliniella occidentalis Pergande (Thysanoptera: Thripidae) cause more direct feeding damage to plants than the adults. We, therefore, investigated the behaviour-modifying effects on second instar larvae of two jasmonic acid derivatives. The artificial application of methyl jasmonate and cis-jasmone, both at 1 % concentration, deterred the larvae from settling in a dual choice bean leaf disc assay. We observed a dose-dependent feeding deterrence of both jasmonates and calculated the concentration required to reduce the feeding damage by 50 % relative to the control treatment (FDC50) for each jasmonate. The feeding damage was reduced by the application of cis-jasmone at 1 % concentration, but not by the jasmonates at the respective FDC50 in no-choice leaf disc bioassays. However, significantly more larvae left jasmonate-treated whole potted bean plants by migrating to the soil compared with control plants. Our results may be exploited extending behavioural manipulation by using plant compounds in thrips control programmes to the full lifecycle of the pest. Plant compounds could be used in integrated and biological pest management strategies against F. occidentalis in combination with the application of various above and below ground control measures.

Using plant chemistry and insect preference to study the potential of Barbarea (Brassicaceae) as a dead-end trap crop for diamondback moth (Lepidoptera: Plutellidae).

Barbarea vulgaris R. Br. has been proposed as a dead-end trap crop for diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae), because its larvae do not survive on this plant species despite being highly preferred for oviposition. We compared plants of several species, varieties, and types in the genus Barbarea (Brassicaceae) to study their potential as trap crops for P. xylostella. In terms of insect behavior, Barbarea plants were assessed based on the criteria of high oviposition preference by P. xylostella moths (compared to other Barbarea plants and to three Brassica oleracea L. crop varieties) and low survival of P. xylostella larvae. Barbarea plants were also assessed based on the criteria of high content of glucosinolates, which stimulate adult oviposition and larval feeding in P. xylostella, and high content of saponins, which are detrimental to survival of P. xylostella larvae. All Barbarea plants tested were preferred over cabbage by ovipositing P. xylostella. Among Barbarea plants, few significant differences in oviposition preference by P. xylostella were found. Ovipositing P. xylostella preferred B. vulgaris plants containing mainly 2-phenylethylglucosinolate over B. vulgaris plants containing mainly (S)-2-hydroxy-2-phenylethylglucosinolate, and P-type B. vulgaris var. arcuata plants over Barbarea rupicola and B. vulgaris var. variegata plants. Despite containing a lower content of saponins than other Barbarea plants tested, Barbarea verna did not allow survival of P. xylostella larvae. Our studies show that, except for B. rupicola and P-type B. vulgaris var. arcuata, which allowed survival of P. xylostella larvae, all Barbarea plants tested have potential as dead-end trap crops for P. xylostella.

Feeding Deterrence of Cabbage Looper (Lepidoptera: Noctuidae) by 1-Allyloxy-4-Propoxybenzene, Alone and Blended With Neem Extract.

The cabbage looper, Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae), is one of the most damaging insect pests of cabbage (Brassica oleracea variety capitata) and broccoli (B. oleracea variety italica) in North America. Leaf-feeding larvae attack crucifer and vegetable crops in greenhouses and fields. Here, we have studied a synthetic feeding deterrent, 1-allyloxy-4-propoxybenzene, and a botanical deterrent, neem (an extract from seeds of Azadirachta indica A. de Jussieu (Meliaceae)), in leaf disc choice bioassays with T. ni. We tested the two deterrents and the combination, and we found that the blend exhibits synergy between the two deterrents. We also tested the deterrents in assays with whole cabbage plants in ventilated enclosures and found that 1-allyloxy-4-propoxybenzene evaporated and, therefore, in that context addition of 1-allyloxy-4-propoxybenzene to neem did not enhance deterrence against T. ni.

The palatability of Arctic willow for greater snow geese: the role of nutrients and deterring factors.

Temporary feeding on willow buds and leaves by nesting greater snow geese provided us with an opportunity to test the relative importance of nutrients and deterrents in affecting the palatability for geese of a food plant with a high phenol content. Protein, total phenol and fiber (neutral and acid detergent fiber, and lignin) were analyzed in closed and open buds and in rolled and open leaves. Geese feed on willows at the open-buds and rolled-leaf stages but not at the closed-bud and open-leaf stages. Protein content was higher in open buds and rolled leaves (25-27%) than in closed buds and open leaves (19-21%). Phenol content increased during leaf emergence but was already high (14%) in rolled leaves. All plant fibers were very high in closed buds but declined rapidly during leaf emergence. The increase in phenol: protein ratio appeared to be more important than phenol concentration alone in explaining the cessation of feeding by geese on willow leaves whereas the high fiber content of closed buds may explain why they were not eaten. Our results illustrate the value of a multifactorial approach in the study of the food selection process in herbivores.

The watercress glucosinolate-myrosinase system: a feeding deterrent to caddisflies, snails and amphipods.

Watercress (Nasturtium officinale) possesses the glucosinolate-myrosinase system. This system is regarded as a classic example of chemical defense for terrestrial crucifers. Damage of watercress initiates myrosinase-mediated hydrolysis of phenylethyl glucosinolate to a toxic endproduct, phenylethyl isothiocyanate. In multiple choice tests, the amphipod Gammarus pseudolimnaeus, the limnephilid caddisflies Hesperophylax designatus and Limnephilus sp., and the physid snail Physella sp. all strongly preferred (10X) yellowed senescent watercress (FY) over fresh green watercress (FG), despite the 2X higher nitrogen content of green watercress (6.9% for FG vs 3.8% for FY). Green watercress contained 10-40 X more glucosinolate than FY watercress (6.4-8.5 mg/g wet for FG vs 0.2-0.7 mg/g wet for FY). However, when the watercress was heated (ca 70°C), to deactivate the myrosinase enzyme, multiple choice tests showed that these species shift their preferences to heated green watercress (HG). Heating deactivated the deterrent effect and overall preference (consumption) was HG ≥ HY > FY ≫ FG for Gammarus. HG > HY ≥ FY ≫ FG for Hesperophylax, HG > FY ≥HY ≥ FG for Limnephilus, and HG ≥ FY > HY ≥ FG for Physella. Thus heating resulted in a shift in preference from the low glucosinolate, but low nitrogen, unheated yellowed tissue to the high nitrogen green tissue. These results suggest that deactivation of the myrosinase enzyme, and hence isothiocyanate production, results in a shift in preference. Preliminary results with Hesperophylax indicate that addition of myrosinase to the test water, which resulted in the formation of isothiocyanate, results in a significant decrease in HG consumption from control levels (p < 0.001) and no change in preference for HY watercress. With Gammarus, myrosinase resulted in reduced consumption of both green and yellowed watercress, but no significant differential effect. These results provide evidence that the glucosinolate-myrosinase system, recognized as the principle deterrent system of terrestrial crucifers, is the feeding deterrent in watercress and also suggest that in the absence of a functioning deterrent system, nitrogen content may influence consumption.

The role of phenolic compounds and nutrients in determining food preference in greater snow geese.

We tested Buchsbaum's hypothesis that food palatability in geese is determined by a hierarchy of feeding cues among which deterrent secondary metabolites (mostly phenols) have a primary role (Buchsbaum et al. 1984). In preference tests, greater snow goose feeding was slightly depressed when grass was sprayed with ferulic acid but not when grass was sprayed with p-coumaric and tannic acids. Extracts of Timothy grass, red clover or alfalfa sprayed on grass also failed to depress goose feeding. In a multifactor experiment, phenol and protein content and height of grass were manipulated simultaneously. When ferulic acid was sprayed, protein and phenol content interacted in determining goose feeding preferences; protein content had no effect in the absence of phenol but did have an effect when phenol was added. When tannic acid was used in a similar experiment, results were inconclusive because of a significant and complex interaction between protein content and height of grass. Our results generally failed to support Buchsbaum's hypothesis that phenol content of plants has a primary role in determining food preference in geese. Protein content of plants seemed to be a more important factor.