Biological control is the suppression of populations of pests and weeds by living organisms. These organisms can provide important protection from invasive species and protect our environment by reducing the need for pesticides. However, they also pose possible environmental risks, so biological control interventions must be undertaken with great care. This book enhances our understanding of biological control interactions by combining theory and practical application. Using a combination of historical analyses, theoretical models and case studies, with explicit links to invasion biology, the authors cover biological control of insects, weeds, plant pathogens and vertebrate animals. The book reflects increasing recognition of risks over the past 20 years, and incorporates the latest technological advances and theoretical developments. It is ideal for researchers and students of biological control and invasion biology.

Biological Control: Ecology and Applications

The predator and parasitoid fauna associated with cereal aphids is described, emphasizing the fauna associated with classical biological control efforts against the greenbug and Russian wheat aphid. We focus on literature from North America and include work from Europe and elsewhere when it is desirable to draw contrasts between approaches that affect cereal aphid biological control. Effects on natural enemies of cereal aphids are described that appear associated with plant traits that are innate, bred, or induced by aphid feeding. Examples of habitat manipulations, within and bordering cereal fields and within the broader landscape in which cereal production resides, affecting predators and parasitoids of cereal aphids are presented. These mediating effects of host plant and habitat manipulations on cereal aphid biological control provide significant and underexplored avenues to optimize cereal aphid management.

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Biological control of cereal aphids in north america and mediating effects of host plant and habitat manipulations.

1. We analysed data collected in 1985-89 from cereal fields to elucidate the relationships between the primary parasitoids and hyperparasitoids of cereal aphids. The analysis aimed to establish whether or not hyperparasitoids interfere with the impact of primary parasitoids on cereal aphid populations. 2. From more than 10000 parasitized aphids, 14 primary parasitoid and 18 hyperparasitoid species were reared. The five most common hyperparasitoids attacked the five most common primary parasitoids, which, in turn, parasitized most frequently the most abundant aphid species, Sitobion avenae (F.). 3. Levels of aphid primary parasitism never exceeded 33%, whereas levels of hyperparasitism often reached 100% in the latter part of the season. However, the low rates of aphid primary parasitism could not have been solely the result of hyperparasitism: if primary parasitoid females which emerged early continued to deposit eggs before the collapse of the aphid populations, those females should have been numerous enough to parasitize large numbers of their hosts before hyperparasitoid pressure became high. 4. We hypothesize that primary parasitoid females leave areas which develop high hyperparasitoid densities. A multiple linear regression model was used to test the hypothesis. The observed declines of aphid primary parasitism were quantitatively related to hyperparasitoid density. 5. The results of this study and additional theoretical considerations are in favour of the above hypothesis. However, other factors such as mortality other than that due to hyperparasitoid attack, and aestivation acting together may also contribute to the low abundance of primary parasitoid females later in the season.

The relationship between primary parasitoids and hyperparasitoids of cereal aphids: an analysis of field data

Bioassays of nicotine and imidacloprid against clones of Myzus persicae (Sulzer) and Myzus nicotianae (Blackman) from around the world demonstrated that some had low levels of resistance to both compounds. This was expressed not only as a reduced mortality, but more markedly as differential inhibition of feeding by imidacloprid concentrations in the parts per billion range. Such concentrations also reduced aphid fecundity by inhibiting the production and viability of nymphs, and this effect was more marked for susceptible aphids than for those showing reduced direct lethal and antifeedant effects.

Lethal and Sublethal Effects of Imidacloprid on Nicotine-Tolerant Myzus nicotianae and Myzus persicae

The rate at which biological control agents disperse from release sites has important implications for their establishment and spread Low rates of dispersal can yield spread that is too slow and may necessitate redistribution efforts for importation biological control and a high density of release sites for augmentation Low dispersal rates may also lead to inbreeding at the site of release On the other hand, high rates of dispersal can lead to Allee effects at the leading edge of the invasion front, potentially reducing the likelihood of establishment Given these disadvantages associated with both low and high dispersal rates, we argue that intermediate rates of dispersal are likely to maximize the probability of establishment and appropriate spread for biological control agents released in the context of either importation or augmentative biological control We consider this putative relationship a ‘Goldilocks hypothesis’ since it posits an optimum at intermediate values In this review paper we begin by discussing the rationale for the Goldilocks hypothesis and then provide a case study from our work on importation biological control of the soybean aphid, Aphis glycines Work on the soybean aphid parasitoid Binodoxys communis has shown that long-distance dispersal of immature parasitoids within winged migrating aphids is unlikely This is likely good news for importation biological control because parasitoids dispersed in this manner would likely encounter crippling Allee effects On the other hand, results from a field release study also suggest that female B communis females (but not males) disperse actively from release sites This female-biased dispersal may lead to strong mate-finding Allee effects and therefore may make establishment less likely

A ‘Goldilocks’ hypothesis for dispersal of biological control agents

The dynamics of migration of the parasitoids Aphidius spp. between grassland and cereal fields of varying sowing dates was investigated in southern England in 1980 and 1981. Using baffled water traps, direct evidence of migration of A. rhopalosiphi De Stefani Perez females from grassland to winter wheat was obtained in June 1980, suggesting that the early-maturing grassland aphid Metopolophium festucae (Theobald) can act as a reservoir of cereal aphid parasitoids. In 1981, estimates of parasitoid production in cereal fields containing the aphids Sitobion avenae (F.), M. dirhodum (Walker) and Rhopalosiphum padi (L.) were compared with actual numbers to calculate net immigration and emigration. Barley and early-sown wheat (drilled before 14 October) proved to be significant sources of Aphidius spp., with one wheat field generating sufficient parasitoids in May to account for immigration into about 25 late-sown fields. Parasitoid migration as larvae inside aphid alatae was apparently of considerably less significance than that by adults, which were predominantly female. The advantages of early drilling of cereals to form ‘semi perennial’ reservoirs of beneficial insects is discussed and weighed against the corresponding disadvantages, especially an increased risk of barley yellow dwarf virus (BYDV).

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0007485300012050

Migration of parasitoids (Hymenoptera: Braconidae) of cereal aphids (Hemiptera: Aphididae) between grassland, early-sown cereals and late-sown cereals in southern England.

V. T. Vorley

Papers

Migration of parasitoids (Hymenoptera: Braconidae) of cereal aphids (Hemiptera: Aphididae) between grassland, early-sown cereals and late-sown cereals in southern England.