Arbuscular mycorrhizal fungi (AMF) can increase plant nutrient uptake and chemical defense production, both of which can improve plants’ ability to resist insect herbivory. Cover crops—non-commercial species planted in between cash crops in a crop rotation—can naturally alter both soil nutrients and AMF. We tested whether different cover crop species alter AMF colonization, plant nutrient status and plant–insect interactions in a subsequent maize crop. Cover crop species were either non-mycorrhizal, non-leguminous (canola, forage radish), mycorrhizal non-leguminous (cereal rye, oats), mycorrhizal leguminous (clover, pea) or absent (fallow). We measured the cascading consequences of cover crop treatment on maize root AMF colonization, maize growth and performance of an herbivorous insect (European corn borer) feeding on the maize. Maize AMF colonization was greater in plots previously planted with mycorrhizal (rye, oats) than non-mycorrhizal (canola, radish) cover crops or no cover crop (fallow). AMF colonization was linked to increased plant phosphorous and nitrogen, and maize growth increased with low plant N:P. Induced jasmonic acid pathway plant defenses increased with increasing maize growth and AMF colonization. European corn borer survivorship decreased with lower plant N:P, and insect development rate decreased with increased induced plant defenses. Our data describe a cascade in which cover crop species selection can increase or decrease mycorrhizal colonization of subsequent maize crop roots, which in turn impacts phosphorus uptake and may affect herbivory resistance in the maize. These results suggest that farmers could select cover crop species to manage nutrient uptake and pest resistance, in order to amend or limit fertilizer and pesticide use.

Nosema pyrausta is an important microsporidian pathogen of the European corn-borer, Ostrinia nubilalis (Pyralidae), a major pest of corn (maize). The population dynamics of the interaction between the moth and its pathogen have been studied previously using simple models phrased as coupled differential equations, and using large simulation models containing over 150000 coupled equations. A middle approach is adopted here and the interaction studied using an age-structured model written as a system of delay-differential equations. Although the model contains twenty four parameters, estimates for twenty of these were available in the literature. Our model provides a good qualitative match to observed within and between season dynamics and suggests which aspects of the interaction are most important in determining the nature of the system's population dynamics. More generally, we argue that in the absence of better data on insect-disease interactions in natural habitats, valuable insights can be gained by studying equivalent systems in agro-ecosystems. We also argue that models of intermediate complexity that incorporate considerable detail about the natural history of individual interactions, but which are derived from the classical models of animal ecology and epidemiology, offer the most profitable way of modelling insect-pathogen interactions in the wild.

The reliable use of purified Cry1Ab protein standards is a prerequisite for ecological studies and resistance monitoring programs of Cry1Ab-expressing transgenic corn. In this study the stability and activity of different Cry1Ab protein batches expressed in and purified from Escherichia coli were determined during two-year storage at different temperature conditions (4 °C, –20 °C, and –80 °C). SDS-Polyacrylamide gel electrophoresis showed degradation of the protein stored at 4 °C over four months, whereas no difference in the band intensity of the Cry1Ab proteins stored at –20 °C and –80 °C was observed. Bioassays with neonate larvae of Ostrinianubilalis indicated that the biological activity of Cry1Ab varied from batch to batch, depending on the production process. Cry1Ab protein stored at 4 °C for four months showed a significantly decreasing activity measured as median lethal concentration (LC50), whereas the protein activity declined less than 11-fold after two years storage at –20 °C. When stored at –80 °C the toxin activity remained relatively stable for at least 30 months, as indicated by low LC50 values of 7–10 ng Cry1Ab per cm2 diet. These experiments demonstrate that appropriate long-term storage conditions of Cry1Ab protein standards are crucial for resistance monitoring programs of Bt corn, and storage at –80 °C is recommended.

A two-year field study was conducted to evaluate the effectiveness of Trichogramma ostriniae Pang et Chen (T.o.) releases in combination with habitat modification, to enhance biological control of European corn borer (ECB), Ostrinia nubilalis Hübner, the key pest of bell peppers in Kentucky. A randomized block design with a split-plot treatment arrangement was used in both years. Buckwheat, Fagopyrum esculetum Moench, was inter-planted as a nectar source for the wasps and as an attractant for ECB natural enemies. Sentinel ECB egg masses were placed in each subplot to monitor establishment and dispersal of T. ostriniae within and between plots. Fruit were harvested at maturity, graded according to USDA standards, inspected for insect damage, and dissected to confirm ECB presence when evidence of entry was suspected, to determine percentage of infested fruits. Percent ECB infested fruit was reduced in plots with wasp releases and in plots with buckwheat inter-planted. The interaction of habitat modification and wasp releases significantly reduced pepper damage as a result of the synergy between tactics. Percentage of T. ostriniae parasitized sentinel eggs was significantly higher in wasp release plots compared to non-release plots. T. ostriniae releases used in conjunction with habitat modification for ECB control in bell peppers appears to be a promising alternative to traditional insecticide-based strategies for small-acreage and organic farms. This study displays an example system utilizing conservation biological control at a landscape level for pest suppression.

A major assumption of the high-dose/refuge strategy proposed for insect resistance management strategies for transgenic crop plants that express toxins from Bacillus thuringiensis is that resistance traits that evolve in pest species will be recessive. The inheritance of Cry1F resistance and larval survival on commercially available Cry1F corn hybrids were determined in a laboratory-selected strain of European corn borer, Ostrinia nubilalis (Hübner), displaying more than 3000-fold resistance to Cry1F. Concentration-response bioassays of reciprocal parental crosses indicated that the resistance is autosomal and recessive. Bioassays of the backcross of the F1 generation with the selected strain were consistent with the hypothesis that a single locus, or a set of tightly linked loci, is responsible for the resistance. Greenhouse experiments with Cry1F-expressing corn hybrids indicated that some resistant larvae survived the high dose of toxin delivered by Cry1F-expressing plants although F1 progeny of susceptible by resistant crosses had fitness close to zero. These results provide the first direct evidence that the high dose/refuge strategy currently in place to manage resistance in Cry1F-expressing corn is appropriate.

Changes in host preferences are thought to be a major source of genetic divergence between phytophagous insect taxa. In western Europe, two sympatric taxa, O. nubilalis (the European corn borer) and O. scapulalis, feed mainly on maize and hop or mugwort, respectively. These two species may have diverged without geographic isolation after a host shift of ancestral populations onto maize or another cultivated species (e.g. sorghum). A previous study using inbred laboratory strains revealed that the two species differ in their oviposition choices in maize-mugwort tests. We sampled four natural populations in France (two of each taxon) and tested their oviposition behaviour toward four of their main host plant species: maize, sorghum, mugwort and hop. O. nubilalis females showed a very high preference for laying their eggmasses on maize, whereas O. scapulalis females displayed a more balanced range of preferences. O. nubilalis females were attracted slightly to sorghum, suggesting that this plant is an accidental, rather than a regular and ancestral host plant of O. nubilalis. One important result arising from this study is the significant proportion of eggs laid by both Ostrinia species on hop. This may explain why some stands of hop are sometimes not only infested by O. scapulalis but also by O. nubilalis larvae, a situation preventing assortative mating based on microallopatry. Hence, further studies must be conducted to see whether the host preference in the genus Ostrinia might be linked to assortative mating by a mechanism that is not mediated by the host plant.

In this study, we evaluated in field trials the effects on non-target species, of transgenic corn producing the Cry1Ab toxin of Bacillus thuringiensis (Bt). In 1998, we collected Ostrinia nubilalis (Hübner) larvae from transgenic Bt corn (Novartis Hybrid 176) and non-Bt corn at four geographical sites. We found a significant variation in parasitism by the tachinids Lydella thompsoni (Herting) and Pseudoperichaeta nigrolineata (Walker) among sites, and more parasitism in non-Bt than in Bt fields. The Bt effect did not vary significantly among fields. In 1999, we performed a field experiment at two sites, comparing the temporal abundance of non-target arthropods in Bt corn (Monsanto Hybrid MON810) and non-Bt corn. The non-target insects studied included the aphids Metopolophium dirhodum (Walker), Rhopalosiphum padi (L.) and Sitobion avenae (F.), the bug Orius insidiosus (Say), the syrphid Syrphus corollae (Meigen), the ladybird Coccinella septempunctata (L.), the lacewing Chrysoperla carnea (Stephens), thrips and hymenopteran parasitoids. For all species but one, the number of individuals varied greatly over the season but did not differ between the types of corn. The only exception was thrips which, at one site, was significantly more abundant in Bt corn than in non-Bt corn. However this difference did not remain significant when we took the multiple tests into account. Implications for pest resistance management, population dynamics and risk assessment are discussed.

Since the introduction of irrigation in the early 1950s major changes in the crop regime have taken place in Israel. These changes had greatly influenced the populations of the four species of corn borers found in Israel. Chilo agamemnon, which was the main pest during the 1960s decreased and the numbers of Sesamia nonagrioides increased. The reduction in the sorghum acreage, caused a decrease in the numbers of Sesamia cretica. In 1981 an increase in the numbers of the European corn borer, Ostrinia nubilalis, was observed. At present S. nonagrioides and O. nubilalis are the main corn pests in Israel.

Chilo agamemnon was first recorded in Israel in 1959 near the Gaza strip. In the course of 2–3 years it became a very serious pest in the southern parts of the country. Later, the spread of the pest continued throughout the country. Since 1973 a drastic decrease in the populations of C. agamemnon was recorded. The probable reasons for the decrease in the populations of this pest in Israel are:

(1) The relative increase of the areas of sweet corn, which is not its preferable host plant.

(2) Rice and sugar-cane, which are very important host plants in Egypt, are not grown in Israel.

Field experiments against C. agamemnon, carried out when populations were high, showed that dust applications were more effective than sprays.