Half of all insect species are dependent on living plant tissues, consuming about 10% of plant annual production in natural habitats and an even greater percentage in agricultural systems, despite sophisticated control measures. Plants are generally remarkably well-protected against insect attack, with the result that most insects are highly specialized feeders. The mechanisms underlying plant resistance to invading herbivores on the one side, and insect food specialization on the other, are the main subjects of this book. For insects these include food-plant selection and the complex sensory processes involved, with their implications for learning and nutritional physiology, as well as the endocrinological spects of life cycle synchronization with host plant phenology. In the case of plants exposed to insect herbivores, they include the activation of defence systems in order to minimize damage, as well as the emission of chemical signals that may attract natural enemies of the invading herbivores and maybe exploited by neighbouring plants that mount defences as well.

Insect-plant biology

Studies of agroecosystems during the past 30 years have lead several agri­ cultural scientists to question the commitment of modem industrial agriculture to high intensity monocultural production . Additionally, current research directions in integrated pest management emphasize biological interactions among insect pests, natural enemies, and other crop pests, such as weeds. These inquiries have led to a recent rebirth in interest and research activities on cultural and biological controls in entomology . Vegetational diversity plays a central role in this research renaissance. If one considers it broadly, vegetational diversity involves mixing different kinds of plants in a plant community, but, to paraphrase Vilfredo Pareto ( 1 12), vegetational diversity appears like a bat; within it one can find both birds and mice . More specifically, vegetational diversity varies in three ways: the kinds, the spatial array, and the temporal overlap of the plants in the mixture. In most cases, the mixed plants are different plant species. These plants might be two crops, which is called intercropping; a crop and a weed, which is called weedy culture; or a crop and a beneficial noncrop, which is known by many names including nursery crops, living-mulches, cover­ cropping, etc . In some cases, however, different plant genotypes are mixed (41), including polyvarietal mixtures of agronomically dissimilar genotypes

Vegetational Diversity and Arthropod Population Response

This review surveys the occurrence, analysis, and properties of glucosinolates and derived compounds in plants and products intended for humans and animal consumption. The paper, which includes references published in 1981, is also intended to compliment existing reviews on the chemistry of these sulfur‐containing natural products. Particular emphasis is placed upon members of the Brassica family because of their importance as vegetables, condiments, oilseeds, and animal feedingstuffs. Since much of the work considered here relates to glucosinolate decomposition products, biochemical information concerning the nature, occurrence, and properties of the glucosinolate‐degrading enzyme, myrosinase, is considered in Section III. The methods available for the chemical analysis of glucosinolates and their various breakdown products are discussed critically. Factors affecting the glucosinolate content of plants and plant products arc outlined in Section VII. Particular emphasis is placed upon the effect of proces...

Glucosinolates and their breakdown products in food and food plants

Push-pull strategies involve the behavioral manipulation of insect pests and their natural enemies via the integration of stimuli that act to make the protected resource unattractive or unsuitable to the pests (push) while luring them toward an attractive source (pull) from where the pests are subsequently removed. The push and pull components are generally nontoxic. Therefore, the strategies are usually integrated with methods for population reduction, preferably biological control. Push-pull strategies maximize efficacy of behavior-manipulating stimuli through the additive and synergistic effects of integrating their use. By orchestrating a predictable distribution of pests, efficiency of population-reducing components can also be increased. The strategy is a useful tool for integrated pest management programs reducing pesticide input. We describe the principles of the strategy, list the potential components, and present case studies reviewing work on the development and use of push-pull strategies in each of the major areas of pest control.

The Use of Push-Pull Strategies in Integrated Pest Management

In this paper we argue that landscape spatial structure is of central importance in understanding the ef- fects of fragmentation on population survival. Landscape spatial structure is the spatial relationships among habitat patches and the matrix in which they are embedded. Many general models of subdividedpopulations make the assump- tions that (1) all habitatpatches are equivalent in size and quality and (2) all local populations (in the patches) are equally accessible by dispersers. Models that gloss over spa- tial details of landscape structure can be useful for theoret- ical developments but will almost always be misleading when applied to real-world conservation problems. We show that local extinctions of fragmented populations are com- mon. From this it follows that recolonization of local ex- tinctions is criticalfor regional survival offragmented pop- ulations. The probability of recolonization depends on (1) spatial relationships among landscape elements used by the population, including habitat patches for breeding and ele- ments of the inter-patch matrix through which dispersers move, (2) dispersal characteristics of the organism of inter- est, and (3) temporal changes in the landscape structure. For endangered species, which are typically restricted in their dispersal range and in the kinds of habitat through which they can disperse, these factors are of primary importance and must be explicitly considered in management decisions.

https://www.jstor.org/stable/info/2386720

Conservation of fragmented populations

SUMMARY

To determine the relative importance of different potential host plants for supporting populations of the cabbage root fly, wild and cultivated crucifers were sampled for pupae at four locations during 1971-3. In addition, eighty-three species of Cruciferae native to or naturalized in the British Isles were inoculated with cabbage root fly eggs in a glasshouse to determine which species could support the larvae.



In the field, most pupae (28-7/plant) were collected from untreated cauliflowers. Fewer pupae (i-7–8-6/plant) were obtained from untreated crops of Brussels sprout, cabbage and swede. Applications of chlorfenvinphos reduced populations to two or less pupae per plant on all crops. Of five common weed species sampled, only Raphanus raphanistrum produced as many pupae as certain of the untreated brassica crops. Pupae did not occur in samples from Capsella bursa-pastoris but Sisymbrium officinale, Thlaspi arvense and Sinapis arvensis usually supported low numbers.



In the glasshouse, only forty-four of the eighty-three cruciferous species tested supported larval development. Most pupae were obtained from 12-wk-old plants of Barbarea intermedia. B. stricta, Brassica napus, Cochlearia officinalis and R. raphanistrum and from 24-wk-old plants of Brassica rapa, Erysimum aureum, Cochlearia anglica and C. officinalis. Plant age considerably affected pupal production. Plants within a genus often gave similar results, pupae not being recovered from any of the Diplotaxis or Arabis species tested, or from young plants of Erysimum spp. In other families, Reseda lutea and R. luteola supported larval development, but the widely-separated Plantago major did not.



Arguments for and against the removal of cruciferous weeds from the vicinity of cruciferous crops are discussed.

Cultivated and wild host plants supporting populations of the cabbage root fly

Volatile plant chemicals are generally credited with a major role in host plant location by many phytophagous insects. Mixtures of volatiles are produced in cruciferous plants mainly by the hydrolysis of non-volatile glucosinolates to volatile isothiocyanates, thiocyanates and nitriles. The cabbage root fly attacks a wide range of cruciferous plants, with differing odours, implying that several volatile chemicals are probably involved in attracting the flies and in stimulating them to lay. Oviposition by the cabbage root fly was studied, therefore, on a large range of wild and cultivated plants to determine the most preferred species. The volatile chemicals in these species were identified in the hope that some of them may prove more useful as attractants for luring cabbage root flies to field traps. Similar volatile chemicals were released from both intact and macerated plants. It was deduced that any one, or combinations, of eleven chemicals may probably be involved in attraction and host plant selection by this fly. The concentrations of these chemicals change during the life of the plant, however, and an initially attractive chemical can become so concentrated that eventually it repels the insect. Difficulties encountered in experiments on olfaction and possible ways in which they can be overcome are discussed.



RESUME

INFLUENCE DES SUBSTANCES CHIMIQUES VOLATILES DUR LA DECOUVERTE DES PLANTES HOTES PAR LA MOUCHE DU CHOU (DELIA BRASSICA)



Les substances volatiles des vegetaux sont considerees comme jouant un role capital dans la decouverte de la plante hote. L'hydrolyse des glucosinolates non volatils en isothiocyanates, thiocyanates et nitriles volatils produit essentiellement les melanges volatils des Cruciferes. Comme la Mouche du Chou attaque une gamme importante de Cruciferes aux odeurs differentes, ceci implique que plus d'une substance volatile est probablement impliquee dans l'attraction des mouches et la stimulation de leur ponte. La ponte de la Mouche du Chou a ainsi ete etudiee sur de nombreuses plantes sauvages et cultivees pour determiner les especes preferees. Les substances volatiles de ces especes ont ete identifiees dans l'espoir que certaines pourraient s'averer utiles pour attirer les Mouches du Chou dans les pieges. Des substances volatiles semblables ont ete liberees par les plantes intactes et macerees. On en a deduit, que l'une quelconque, ou des combinaisons, de 11 substances peuvent etre impliquees probablement dans l'attraction et la selection des plantes hotes par cette mouche. Cependant leurs concentrations changent pendant la vie de la plante et une substance d'abord attractive peut devenir tellement concentree qu'elle repousse eventuellement l'insecte. Les difficultes experimentales de l'olfacation et des methodes pour les surmonter sont discutees.

Volatile plant chemicals and their effect on host plant finding by the cabbage root fly (delia brassicae)

A method for continuously rearing cabbage root fly, Erioischia brassicae (Bch.) is described.Adult flies fed on sucrose, brewers’ yeast and yeast hydrolysate laid an average of 220 eggs per female when caged together in large numbers and 376 eggs per female when caged singly. Egg viability was 86 per cent. Egg hatch was severely reduced by relative humidities of less than 90 per cent, and the embryo became more susceptible to desiccation as it matured. The larvae were reared on swede, and maximum survival was obtained when the swedes were inoculated with an optimum number of eggs calculated from the ratio of 1 egg: 1.6 g. of swede. Different ratios were obtained from turnip and winter radish indicating that survival was probably related to the nutritional value of the rearing medium as well as to its availability. An average of 68 per cent, of the eggs placed on swede produced pupae that were equivalent in size to wild pupae. The fecundity of the flies was directly related to pupal weight and to the availability of protein in their diet. Adult longevity was reduced more by mutual disturbance than by any other factor.

A method for the continuous rearing of the cabbage root fly Erioischia brassicae (Bch.) and some observations on its biology

Using mimics of real plants, we found that female cabbage root flies, Delia radicum (L.), detected plants within host patches at least partly on the basis of leaf colour and area, with leaf pattern playing an insignificant role in the case of multi-leaved plants. Composition of the background, whether bare soil or green grass, did not affect female ability to distinguish between leaf mimics of different colour. The contribution of visual stimuli in eliciting female landings on individual plants within a patch decreased as distance between the plants was increased.



RESUME

Reperage visuel des plantes-hotes par Delia radicum



En utilisant les leurres de veritables plantes, nous nous sommes apercus que les femelles de Delia radicum L. detectaient des plantes dans un lot tout au moins en partie d'apres la couleur et la taille des feuilles, tandis que la forme des feuilles ne jouait qu'un role insignifiant chez les plantes a nombreuses feuilles. La composition du fond, du sol nu ou de l'herbe verte, ne modifiait pas l'aptitude des femelles a distinguer entre les couleurs des leurres des feuilles. La contribution des stimuli visuels dans l'induction de l'atterrissage des femelles sur des plantes determinees dans un lot diminuait en fonction de la distance entre les plantes.

Visual detection of host plants by cabbage root flies

In experiments in which spectrophotometric reflectance patterns of real leaves were mimicked with mixtures of artists' pigments, leaf color was shown to be a character used by cabbage root flies, before landing on leaves, to discriminate among the host plant cultivars radish, green cabbage, and red cabbage. It may be possible to take advantage of factors that affect leaf color, such as epicuticular bloom, pubescence, and masking of chlorophyll by other pigments, to decrease the attraction of certain pest insects to plants.

https://science.sciencemag.org/content/sci/221/4606/190.full.pdf

S. Finch

Papers

Cultivated and wild host plants supporting populations of the cabbage root fly

Volatile plant chemicals and their effect on host plant finding by the cabbage root fly (delia brassicae)

A method for the continuous rearing of the cabbage root fly Erioischia brassicae (Bch.) and some observations on its biology

Visual detection of host plants by cabbage root flies

Leaf Color Used by Cabbage Root Flies to Distinguish Among Host Plants