H. F. Van Emden

Integrated pest management in practice - pathways towards successful application.

Abstract Examples from perennial and annual crops in temperate and tropical conditions are used to illustrate the research and development approaches that have contributed to use and integration of host plant resistance and biological, cultural and chemical controls. The evidence shows how successes in IPM have depended upon classical experimental approaches continually responding to changing constraints and to novel discoveries, which are being applied increasingly efficiently and intelligently to farm practice. Future developments are discussed in the context of past experience and new technologies. Recent developments of important new approaches that could help revolutionize management of some pest complexes, in particular genetic engineering, semiochemicals and bioinsecticides, are discussed. Much attention has been devoted to strategic modelling in the IPM context which aims to provide novel insights, but there is little evidence of its value to practical IPM; instead it could be used unwisely to encourage accumulation of unnecessary information. In contrast, tactical models are proving increasingly valuable in forecasting the need for and timing of applied controls. Whilst there have been some outstanding developments in practical application of IPM in many developed countries where the ultimate goal is to decrease over-reliance on conventional insecticides, evidence shows that in many developing countries, where the goal is an ecologically sound mix of non-chemical and chemical methods, there remains a crucial need for much more appropriate research and implementation, especially in small farm conditions.

The role of plant chemical cues in determining host preference in the generalist aphid parasitoid Aphidius colemani.

The host preference behaviour of the generalist aphid parasitoid Aphidius colemani was investigated using a Y‐tube olfactometer. Female A. colemani showed a preference for the host‐plant complex on which they had been reared, even though the same aphid host was involved, demonstrating a host plant preference. This preference was not evident when the parasitoids were dissected from their mummies prior to adult emergence. Host plant preference exhibited during host selection appeared to be induced by chemical cues encountered on the mummy case at the time of emergence, but preferences could be changed by subsequent foraging experiences. It is concluded that plant chemical cues play a major role in determining initial preferences through a process of emergence conditioning but that learning processes, involving cues encountered during oviposition in or contact with the host, can modify these initial preferences.

Reactions of adult female parasitoids, particularly Aphidius rhopalosiphi, to volatile chemical cues from the host plants of their aphid prey

Abstract. In Y‐tube olfactometer tests, Aphidius ervi Hal., Trioxyssp., Praon sp., Aphelinus flavus (Nees), Lysiphlebus fabarum (Marsh.) and Aphidius rophalosiphi De Stef. responded positively to the odour of the plant on which aphid mummies containing them had been collected. The response to host plant odour was greater than the response to the odour of host aphids, their honeydew or a combination of the two. The strongest response was to a combination of plant and host aphids. A. rhopalosiphi showed a strong positive response to three wheat volatiles (cis‐3‐hexenyl acetate, cis‐3‐hexen‐1‐ol and trans‐2‐hexenal) as well as to indole‐3‐acetaldehyde (a breakdown product of tryptophan in aphid honeydew). In both olfactometer tests with odours and choice trials with whole plants, newly emerged A. rhopalosiphidistinguished and preferred the variety of wheat on which their development had occurred to other wheat varieties.

Host plant-aphidophaga interactions.

Abstract Allelochemicals in the host plant can affect natural enemies adversely through the passage of plant toxins up the trophic pyramid. Additionally, the size of the host prey may be influenced through the plant, and this in turn affects the size and fecundity of parasitoids. The numerical response of natural enemies to prey density may also be affected by their attraction to plant volatiles, even in the absence of prey. Predators and parasitoids show different functional responses to prey on different host plants. This is related to prey size, to differences in defensive and other behaviours of the prey, and to effects on searching time of natural enemies. These influences are highly relevant to the use of host plant resistance as a pest control technique. The argument that natural enemies may accelerate the selection for plant-adapted biotypes of herbivores, and the production of pest-resistant crop varieties by genetic engineering are modern challenges to the practical exploitation of host plant-Aphidophaga interactions.

Habitat manipulation and natural enemy efficiency: Implications for the control of pests

Publisher Summary The chapter examines the approach to a theoretical understanding of the ecological principles that determine the success of habitat manipulation. It tempers theory with some practical considerations relating to how habitat manipulation research may be undertaken and translated into practical guidance to farmers. The scale over which habitat manipulation can lead to a redistribution of natural enemies has important implications. If redistribution occurs on a relatively large scale, extending over many fields and farms, those growers practicing the technique are expected to derive benefit at the expense of more conservative neighbors, whose natural enemies may emigrate to where food plants (or other features such as overwintering habitat) are available. These natural enemies may then be disinclined to distribute away from such features and so concentrate their predation/parasitism on pests in adjacent crops. One of the greatest challenges faced by those seeking to implement habitat manipulation into Western agricultural systems is the tendency for these to employ heavy rates of pesticides. Although habitat manipulation may provide refugia for natural enemies from pesticide-treated areas, toxic residues left within the crop may repel or disrupt subsequent activity.

Potential of four vegetable oils and ten botanical powders for reducing infestation of cowpeas by Callosobruchus maculatus, C. chinesis and C. rhodesianus

Abstract The possible use of ten botanicals and four vegetable oils in managing the bruchid beetles of legumes, Callosobruchus chinesis, C. maculatus and C. rhodesianus , was investigated. All four oils tested (corn, groundnut, sunflower and sesame) significantly reduced the oviposition of all three bruchid species at 10 ml/kg and also significantly reduced the longevity of adults of C. maculatus and C. chinensis at this dose. Only corn and sunflower oil caused a significant reduction of longevity of C. rhodesianus at 10 ml/kg. The number of eggs laid by all three bruchid species was significantly reduced in treatments to which powders of Cymbopogon citratus, Cinnamomum camphora, Derris inudata, Monodora myristica, Zingiber spectabile or A. zerumbet had been added.

Assays for Insect Feeding

The vital role of plant chemicals in herbivorous insect host choice has long been recognized. Indeed, much of the research on plant-insect interactions has centered on the identification of chemicals important in insect feeding. This chapter summarizes methods of testing nonvolatile chemicals that either elicit or inhibit feeding.

Electrophoretic study of genetic variation in British Myzus persicae (Sulz.) (hemiptera, aphididae)

Thirty-five clones of the green peach aphid, Myzus persicae Sulz., representing a wide range of host plants and geographical origins, were examined electrophoretically. Only 11 of 26 enzymes were active enough for subsequent work. Since genetic crosses are very difficult to make in the parthenogenetic M. persicae, assigning bands to loci and alleles is necessarily arbitrary. Thirty-two isozyme bands were detected. Only two of these (Est-1 and Est-3) migrated to different distances in some clones. This is a very low level of interclone variation, considering the known properties and origins of the clones. The peculiar feeding habits of aphids may perhaps partly explain the inactivity of so many enzymes in M. persicae (which are active in other insects). The scarcity of interclone variation in isozyme migration distance in M. persicae clones may be the result of its fast parthenogenetic reproduction and high migration ability of alates, combined with the effects of natural and artificial selection (e.g., by insecticides). Surviving genotypes may be rather few, each represented by numerous individuals. The only type of widespread electrophoretic variation is in the intensity of two esterase bands (Est-1 and Est-2). Five hypotheses are presented to explain this variation and discussed in view of evidence from other organisms.

Pest, disease and weed problems in pea, lentil, faba bean and chickpea

The plant architecture, chemistry and world distribution of food legumes contribute to the large number of associated pests, diseases and weeds. Early weed control is essential; otherwise the pre-flowering plant has considerable powers of compensation for damage, especially if disease resistant cultivars can be planted. After flowering, the potential for compensation is progressively reduced and so the development of economic thresholds as well as reliable monitoring and forecasting systems are needed to maximise the efficiency of minimum pesticide, chosen carefully to integrate pest and disease management.

Sublethal concentrations of azadirachtin affect food intake, conversion efficiency and feeding behaviour of Spodoptera littoralis (Lepidoptera: Noctuidae)

Sublethal concentrations of azadirachtin incorporated into artificial diet and offered to third-instar larvae of Spodoptera littoralis (Boisduval) prolonged larval instars and reduced food intake. These effects were observed after the treated larvae had been transferred to plain diet; the reduced food intake was therefore a secondary antifeedant effect. Azadirachtin did not influence digestion efficiency but diminished the ability of the larvae to convert both ingested and digested nutrients into growth, particularly immediately after treatment. This effect declined with time once the treatment with azadirachtin had ceased. Growth was more severely reduced than food intake, and the reduction in growth also occurred during periods when food intake was not affected, possibly due to post-ingestive effects.