Paul C. Jepson

Assessment of risk of insect-resistant transgenic crops to nontarget arthropods

An international initiative is developing a scientifically rigorous approach to evaluate the potential risks to nontarget arthropods (NTAs) posed by insect-resistant, genetically modified (IRGM) crops. It adapts the tiered approach to risk assessment that is used internationally within regulatory toxicology and environmental sciences. The approach focuses on the formulation and testing of clearly stated risk hypotheses, making maximum use of available data and using formal decision guidelines to progress between testing stages (or tiers). It is intended to provide guidance to regulatory agencies that are currently developing their own NTA risk assessment guidelines for IRGM crops and to help harmonize regulatory requirements between different countries and different regions of the world.

A metapopulation approach to modelling the long-term impact of pesticides on invertebrates

Two simulation models are presented which predict the impact of local and episodic applications of pesticide on the dynamics of invertebrate metapopulations. Both models assume that invertebrates disperse at particular rates over a matrix of fields and that each field experiences a specific pesticide regime. Model 1 investigates the population dynamics of a polyphagous predator which experiences direct mortality from pesticide exposure but is unaffected by the availability of the targeted pest. Model 2 investigates a similar system but also considers the dynamics of the pest, which is influenced both by predation and by pesticide exposure. Using stability diagrams and isocline portraits we characterize the likely long-term effects of factors such as the frequency and extent of spraying, factors which have hitherto not been widely considered in general pesticide models

Time to death response in carabid beetles exposed to multiple stressors along a gradient of heavy metal pollution.

We investigated the responses of invertebrates inhabiting polluted environments to multiple stressors. Carabid beetles (Pterostichus oblongopunctatus F.) were subjected to food deprivation and insecticide treatment (dimethoate) to resolve trends associated with a gradient of heavy metal pollution. Metal concentrations along the gradient of five sites ranged from approximately 150 to 10,500 mg/kg Zn, 136 to 2600 mg/kg Pb, and 0.84 to 81.9 mg/kg Cd. There was no difference in body mass along the pollution gradient. However, the beetles originating from the most contaminated sites were significantly less tolerant to food deprivation than beetles from the reference site. Median survival time was 120 h for the two most polluted sites, compared with 168 h at the reference site. Beetles from the two most polluted sites were also significantly more susceptible to dimethoate at 0.1 microgram active ingredient/beetle. Median survival times were 12 and 123 h for beetles from the two most polluted sites and 359 h for the reference site. Carabid beetles exposed to chronic pollution, therefore, exhibit elevated susceptibility to additional stressors.

Host location by Aedes aegypti (Diptera: Culicidae): a wind tunnel study of chemical cues

Lactic acid, carbon dioxide and human sweat stimuli were presented singly and in combination to female Aedes aegypti (Linnaeus) within a wind-tunnel system. The take-off, flight, landing and probing responses of the mosquitoes were recorded using direct observation and video techniques. The analyses determined the nature of the response to different stimuli and the concentration ranges within which specific behaviours occurred. A threshold carbon dioxide concentration for taking-off of approximately 0.03% above ambient was detected. Lactic acid and human sweat samples did not elicit take-off when presented alone, however, when they were combined with elevated carbon dioxide, take-off rate was enhanced in most of the combinations tested. Flight activity was positively correlated with carbon dioxide level and some evidence for synergism with lactic acid was found within a narrow window of blend concentrations. The factors eliciting landing were more subtle. There was a positive correlation between landing rate and carbon dioxide concentration. At the lowest carbon dioxide concentration tested, landing occurred only in the presence of lactic acid. Within a window of low to intermediate concentrations, landing rate was enhanced by this combination. At the highest carbon dioxide concentration, landing was however inhibited by the presence of lactic acid. The sweat extract elicited landings in the absence of elevated carbon dioxide. This indicated the presence of chemical stimuli, other than lactic acid, active in the short range. Probing occurred only at low carbon dioxide concentrations and there was no probing when lactic acid alone was tested. There was however probing in the presence of combined stimuli, the level of response seemed to be positively correlated with the ratio of carbon dioxide and lactic acid concentrations.

Field‐scale effects of farming practices on linyphiid spider populations in grass and cereals

Linyphiid spiders were sampled in three grass and four cereal fields, between October 1989–October 1990, and from one grass and one cereal field, from June–August 1991. Population growth and decline were characteristic of field type and pattern of management. Agricultural operations caused large population depletions: insecticide applications, cutting grass for silage and autumn cultivations reduced spider populations by 56% to 96%; heavy grazing caused virtual extinction. Aerial dispersal activity, monitored by water traps, showed high dispersal frequency with highest intensity in June, July and August. The results are discussed with reference to the large‐scale spatial structure of linyphiid spider populations and the use of spatially dynamic models to predict metapopulation size as a function of patterns of crop management, land‐use and landscape structure.

Trends in detoxification enzymes and heavy metal accumulation in ground beetles (Coleoptera: Carabidae) inhabiting a gradient of pollution

Non-specfic carboxylesterase and glutathione S-transferase activity was measured in the ground beetle, Pterosthicus oblongopunctatus (Coleoptera: Carabidae), from five sites along a gradient of heavy metal pollution. A previous study determined that beetles from the two most polluted sites (site codes OLK2 and OLK3) were more susceptible to additional stressors compared with beetles from the reference site (Stone et al., Environ. Pollut. 113, 239-244 2001), suggesting the possibility of physiological impairment. Metal body burdens in ground beetles from five sites along the gradient ranged from 79 to 201 microg/g Zn, 0.174 to 8.66 microg/g Pb and 1.14 to 10.8 microg/g Cd, whereas Cu seemed to be efficiently regulated regardless of metal levels in the soil. Beetle mid- and hindguts were homogenized and the soluble fraction containing glutathione S-transferase (GST) and carboxylesterase (CaE) was assayed using kinetic analyses. Significantly higher levels of GST were found only in female beetles from the most polluted sites (OLK2 and OLK3; P=0.049, P<0.001, respectively) compared with the reference site (OLK7). In addition, OLK3 females had significantly higher levels of CaE compared with the reference beetles (P=0.01). Male beetles did not differ in enzyme activity along the metal gradient. Overall, obvious trends in detoxification enzymes were not detected in ground beetles in association with metal body burdens.

Relative Frequencies of Visits to Selected Insectary Plants by Predatory Hoverflies (Diptera: Syrphidae), Other Beneficial Insects, and Herbivores

Abstract The use of insectary plants in agroecosystems to provide floral resources for enhancing natural enemy activity is an increasingly used practice, but candidate flowering plant species are not always screened for their attractiveness to key arthropods in the system being studied. In the work presented here, the relative attractiveness of four species of insectary plants to beneficial and pest insect species was assessed by observing the relative frequencies of flower visits to replicated blocks of the insectary flowers in two Oregon broccoli fields. The four plant species tested were alyssum (Lobularia maritima L. Desv.), coriander (Coriandrum sativa L.), buckwheat (Fagopyrum esculentum Moench), and phacelia (Phacelia tanacetifolia Benth.). Predatory hoverflies (Syrphidae) were identified to species, where possible, because of their previously observed importance as aphid predators in broccoli fields in the study area. The other beneficial insect groups observed were in the families Apidae, Coccinellidae, Tachinidae, and Vespidae, and the three main pest species were western tarnished plant bug (Lygus hesperus Knight), western spotted cucumber beetle (Diabrotica undecimpunctata undecimpunctata Mannerheim), and imported cabbageworm (Pieris rapae L.). The Syrphidae visited mostly coriander, but this “preference” was probably influenced by competition from other foragers. Bumblebees and the three pest species visited mostly phacelia, and other species groups were less consistent in their flower choices. The different insect preferences for flowers are discussed in terms of the key influencing factors that should be considered when assessing the relative attractiveness of insectary plants in the field.

Effects of honeydew and insecticide residues on the distribution of foraging aphid parasitoids under glasshouse and field conditions

The opposing effects of attraction to host‐derived kairomones and repellency from the pyrethroid insecticide deltamethrin were investigated with aphid parasitoids from the genus Aphidius (Hymenoptera: Aphidiinae). The spatial distribution of female parasitoids was recorded in a series of experiments conducted in a small glasshouse containing wheat plants either infested with cereal aphids, Sitobion avenae (F.) (Homoptera: Aphididae), uninfested or treated with the recommended field concentration of deltamethrin. The number of parasitoids per plant were counted at 0.5 h, 1 h and then at one hourly intervals up to 8 h after release. Parasitoids showed a strong aggregation response to aphid‐infested plants compared to adjacent uninfested plants. With the introduction of insecticide‐treated plants around the aphid‐infested plants, parasitoids showed a greater tendency to disperse away, resulting in fewer parasitoids on plants and significantly lower rates of aphid parasitism. The degree of aphid fall‐off from plants was a good indicator of parasitoid foraging activity. In field studies, using sticky traps to measure the activity of parasitoids in plots sprayed with water, deltamethrin and/or an artificial honeydew solution, repellent properties were evident for up to 2 days after application. The attraction/arrestment stimuli associated with the honeydew solution were sufficient for parasitoids to continue searching insecticide‐treated areas. The implications of these findings for parasitoids searching crops contaminated with aphid‐derived kairomones and insecticides are discussed.

Temporal and spatial changes in aphid and parasitoid populations following applications of deltamethrin in winter wheat

The spatial and temporal effects of the pyrethroid insecticide, deltamethrin, on populations of cereal aphids and their primary parasitoids and hyperparasitoids were investigated in a large scale field experiment in winter wheat. Four hectare plots were treated at the recommended field concentration or a reduced concentration representing one twentieth of field rate. A control plot was left unsprayed. Invertebrate populations were sampled at sites within a grid layout covering the whole plots, enabling the use of geostatistical analysis. Hymenopteran populations were monitored using transparent sticky traps and suction sampling. Aphid populations were recorded by visual counts. Monitoring continued for 36 days after treatment. The full rate deltamethrin treatment resulted in initial reductions of aphid populations by 78%. Primary parasitoid and hyperparasitoid populations were reduced in suction samples by 90% and 47% respectively, when corrected for control fluctuations. The reduced deltamethrin concentration caused reductions of aphid, primary parasitoid and hyperparasitoid populations of 40, 60 and 54% respectively. Aphid population recovery over the full rate plot occurred slowly and in a ‘patchy’ manner following treatment. No significant reinvasion gradients were detected. Aphid population density recovered more rapidly in the reduced rate treatment; with initial evidence for increased densities at the plot centre. Significant patterns of reinvasion were initially detected for both groups of Hymenoptera in the full rate treatment, suggesting that reinvasion of the sprayed area was taking place from untreated surrounding reservoirs. It was concluded that experiments that examine pesticide impacts within small plots will lead to underestimates of effects on dispersive groups including parasitic Hymenoptera.

The influence of insecticide residues on primary parasitoid and hyperparasitoid foraging behaviour in the laboratory

The behaviour of Aphidius rhopalosiphi DeStefani‐Perez (Hymenoptera: Braconidae) was recorded in laboratory bioassays in the presence and absence of both residues of honeydew from the English grain aphid, Sitobion avenae (F.) and the pyrethroid insecticide, deltamethrin. Insecticide concentrations ranged from the field recommended dose rate (6.25 g ai/ha in 200 l water) to 1/16th of field rate. Parasitoids responded strongly to patches of honeydew on filter papers, however the addition of increasing concentrations of deltamethrin caused increasingly early departure from the honeydew‐treated areas. Parasitoids pre‐exposed to field concentration residues for between 1 and 20 min showed shorter retention times and abnormal types of behaviour on honeydew‐treated patches compared to control wasps. Recovery of ‘normal’ behaviour patterns occurred over a 12 h period away from the insecticide source. Further laboratory studies examined the foraging of A. rhopalosiphi and one of its associated hyperparasitoids, Dendrocerus carpenteri (Curtis), on mature wheat plants treated with an artificial honeydew solution and deltamethrin. Wasps exposed to deltamethrin residues were observed to spend shorter visit times, to groom more frequently and to rest less frequently than those on insecticide‐free plants. Differences were found between the distribution of parasitoids on insecticide‐treated and untreated plants, with D. carpenteri showing greater movement down insecticide‐treated plants accompanied with an increase in time spent on abaxial leaf surfaces compared to A. rhopalosiphi. The results are discussed in terms of the repellency of deltamethrin and the implications for integrated pest management of differing sub‐lethal insecticide effects on primary parasitoid and hyperparasitoid behaviour.