European populations of Diabrotica virgifera virgifera are resistant to aldrin,but not to methyl‐parathion

The western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), is a major pest of cultivated corn in North America and has recently begun to invade Europe. In addition to crop rotation, chemical control is an important option for D. v. virgifera management. However, resistance to chemical insecticides has evolved repeatedly in the USA. In Europe, chemical control strategies have yet to be harmonized and no surveys of insecticide resistance have been carried out. We investigated the resistance to methyl‐parathion and aldrin of samples from nine D. v. virgifera field populations originating from two European outbreaks thought to have originated from two independent introductions from North America. Diagnostic concentration bioassays revealed that all nine D. v. virgifera field populations were resistant to aldrin but susceptible to methyl‐parathion. Aldrin resistance was probably introduced independently, at least twice, from North America into Europe, as there is no evident selection pressure to account for an increase of frequency of aldrin resistance in each of the invasive outbreaks in Europe. Our results suggest that organophosphates, such as methyl‐parathion, may still provide effective control of both larval and adult D. v. virgifera in the European invasive outbreaks studied.     

Western corn rootworm adult movement and possible egg laying in fields bordering maize

Abstract:  Western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte, larval damage in maize following soybean was observed in Croatia in 2003 along the edges and within soybean fields which bordered continuous maize fields in previous year. The explanation was that WCR adults moved from the continuous maize to the neighbouring soybean fields to lay eggs. This study was designed to measure how far WCR adults will enter into neighbouring fields to lay eggs. The WCR adult population was monitored in continuous maize fields in 2003 and 2005 by using Pherocon^® AM non-baited yellow sticky traps in the middle and on the borders of the maize field and at different distances and directions into neighbouring fields planted by wheat and soybean. Larval presence and root damage ratings (Iowa State University 1–6 ) were recorded at different locations within the maize field in following years. Approximately, the same concentration of WCR adults was recorded along the edges of the maize fields as recorded in the centres of those fields. A significant number of WCR adults was recorded up to a distance of 50 m into neighbouring fields. Regression analysis showed medium negative correlation between distance from previous maize field and root damage in the following year. Findings indicate that WCR egg lying can reach approximately 20 m into fields neighbouring maize fields and that significant root damage caused by WCR larvae in first-year maize following soybean and wheat can happen up to a distance of 20 m into those fields. Most farmers's fields in Croatia are up to approximately 50 m wide. As an edge effect for WCR egg laying can reach approximately 20 m into fields neighbouring maize fields, our research results indicate that it is possible to see WCR larval damage in rotated fields without those WCR's being the variant form.     

Spatio-temporal dynamics of corn rootworm, Diabrotica spp., adults and their spatial association with environment

Multiyear and multilocation studies were conducted to investigate the within‐ and the between‐year spatial dynamics of corn rootworms Diabrotica spp. (Coleoptera: Chrysomelidae), adults and their spatial associations with environmental factors in cornfields. Grid‐based spatial sampling was conducted by trapping adults emerging from the soil (i.e., ‘emergence‐trap counts’) and by counting the number of adults in the ear zone of corn plant (i.e., ‘ear‐zone count’). Spatial analysis with distance indices (SADIE) was used to determine spatial distribution patterns and to investigate spatial associations. Ear‐zone counts and emergence‐trap counts were spatially dynamic within a year and more frequently aggregated in the middle of growing seasons and random early and late in the season. However, during the peak population periods, spatial distribution of ear‐zone counts and emergence‐trap counts were significantly consistent between years, indicating predictability of future spatial distributions. Spatial distribution of emergence‐trap counts and ear‐zone counts were positively associated with soil moisture and presence of corn plants with silks, respectively. This study demonstrated that within‐year spatial distribution patterns were dynamic and that there was between‐year spatial consistency of corn rootworm adult distributions. Such information can be used to improve preventative management of corn rootworms.     

Polymorphic microsatellite loci from northern and Mexican corn rootworms (Insecta: Coleoptera: Chrysomelidae) and cross-amplification with other Diabrotica spp

The northern corn rootworm (Diabrotica barberi) and Mexican corn rootworm (Diabrotica virgifera zeae) are significant agricultural pests. For the northern corn rootworm, and to a lesser extent, the Mexican corn rootworm, high resolution molecular markers are needed. Here we present 14 polymorphic microsatellite loci isolated from libraries constructed using pooled northern and Mexican corn rootworm genomic DNA. Polymorphism in other Diabrotica, including the banded cucumber beetle, southern corn rootworm and western corn rootworm, is described.     

Factors influencing the aggregative response of the blue willow beetle, Phratora vulgatissima

Crop rotation has traditionally been a valuable method for managing pests, but now a serious insect pest of maize (Diabrotica virgifera virgifera LeConte [Coleoptera: Chrysomelidae]) has developed behavioral resistance to rotation. A simple model of adult behavior and population genetics can explain how this resistance may have developed. This general model indicates that evolution may be caused by selection on a single gene for adult movement and that behavioral resistance only develops at high levels of rotation (>80% of plant landscape). In less diverse landscapes, crop rotation selects for the expansion of host preferences (polyphagy) by adults. More diverse landscapes may delay the evolution of resistance to crop rotation depending on the fitness costs and the nature of the genetic system.     

Genome scan of Diabrotica virgifera virgifera for genetic variation associated with crop rotation tolerance

Abstract:  Crop rotation has been a valuable technique for control of Diabrotica virgifera virgifera for almost a century. However, during the last two decades, crop rotation has ceased to be effective in an expanding area of the US corn belt. This failure appears to be due to a change in the insect's oviposition behaviour, which, in all probability, has an underlying genetic basis. A preliminary genome scan using 253 amplified fragment-length polymorphism (AFLP) markers sought to identify genetic variation associated with the circumvention of crop rotation. Samples of D. v. virgifera from east-central Illinois, where crop rotation is ineffective, were compared with samples from Iowa at locations that the behavioural variant has yet to reach. A single AFLP marker showed signs of having been influenced by selection for the circumvention of crop rotation. However, this marker was not diagnostic. The lack of markers strongly associated with the trait may be due to an insufficient density of marker coverage throughout the genome. A weak but significant general heterogeneity was observed between the Illinois and Iowa samples at microsatellite loci and AFLP markers. This has not been detected in previous population genetic studies of D. v. virgifera and may indicate a reduction in gene flow between variant and wild-type beetles.     

Nutritional resources used by the invasive maize pest Diabrotica virgifera virgifera in its new South-east-European distribution range

Food utilization by adults of the invasive maize (Zea mays L.) (Poaceae) pest western corn rootworm (WCR; Diabrotica virgifera virgifera LeConte) (Coleoptera: Chrysomelidae) was investigated in the south‐eastern part of its new European distribution range. At weekly intervals over a 10‐week period, 10 beetles per field were collected from six fields that had a high abundance of flowering weeds and six fields with a low abundance of flowering weeds, with the aim of understanding adult feeding behaviour in Europe and comparing this behaviour with North American WCR. Gut content analysis was performed to determine the use of maize tissue and weed pollen with regard to maize phenology. Furthermore, all pollen found within the gut was quantified and identified to plant species level. The use of maize tissue by adult WCR changed over time according to maize phenology. Pollen originating from plants other than maize was used more frequently as the maize matured. Adults fed on pollen from 19 of 25 different plant species found in maize fields and showed a preference for the pollen of specific weeds. Pollen from weed species was found more often in beetles from fields with a high abundance of weeds compared to beetles from fields with a low abundance of weeds. Females consumed greater amounts of pollen than males, the latter feeding on a wider diversity of host plants. The pollen resources used by adult WCR in Hungary were more diverse compared to WCR in the USA, which may contribute to the invasion success of WCR in Europe.     

Toxicity and neurophysiological effects of fipronil and fipronil sulfone on the western corn rootworm (Coleoptera: Chrysomelidae)

Fipronil is a member of the relatively new phenylpyrazole insecticide class that is active at the neuro‐inhibitory gamma amino butyric acid (GABA)‐gated chloride channel/ionopore complex. The toxicity and neurophysiological effects of fipronil and its oxidative sulfone metabolite [5‐amino‐1‐(2,6‐dichloro‐4‐trifluoromethylphenyl)‐3‐cyano‐4‐trifluoromethylsulfonylpyrazole] were investigated by using an insecticide‐susceptible western corn rootworm population. In topical bioassays using adult rootworms, fipronil was toxic at very low doses (LD₅₀ = 0.07; LD₉₀ = 0.33 ng/mg). At the LD₉₀, pre‐treatment with the cytochrome P450 monooxygenase inhibitor piperonyl butoxide led to mild antagonism of fipronil toxicity (LD₉₀ = 0.42 ng/mg), while the sulfone analog had greater toxicity (LD₉₀ = 0.22 ng/mg). In neurophysiological studies of spontaneous electrical activity, adult and larval rootworms were equally affected by fipronil and the sulfone analog at 10 μM (in the presence of 5 mM GABA) in comparison to GABA‐treated baselines. Using larval rootworms, insensitivity of the GABA receptor to binding by picrotoxinin or dieldrin (10 μM ) was not apparent in the presence of 5 mM GABA. Further neurophysiological investigation using a range of concentrations (0.625–20.0 μM) on larval rootworms indicated concentration‐dependent effects on bursting activity for both fipronil and the sulfone analog; however, subtle differences were observed between these two compounds. Results indicate that both fipronil and its oxidative sulfone metabolite have similar toxicological and neurological effects on rootworms. Arch. Insect Biochem. Physiol. 40:150–156, 1999. © 1999 Wiley‐Liss, Inc.     

Insecticidal activity of Cry3Bb1 expressed in Bt maize on larvae of the Colorado potato beetle, Leptinotarsa decemlineata

Environmental risk assessment for genetically modified crops producing insecticidal Cry proteins derived from Bacillus thuringiensis (Bt) includes the evaluation of adverse effects on non-target organisms. Although ELISA concentration measurements indicate the presence of Cry proteins, sensitive insect bioassays determine whether there is biological activity. The insecticidal activity of the coleopteran-active Cry3Bb1 expressed in different tissues of Bt maize, contained in maize-fed herbivores, and in spiked soil was measured in sensitive insect bioassays using larvae of the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae). Biological activity was confirmed of Cry3Bb1 contained in pulverized Bt maize pollen, roots, leaves, silk, and Bt maize-fed spider mites and western corn rootworm adults. When test substances were incorporated into artificial diet at the same concentrations of Cry3Bb1 (measured by ELISA), maize pollen and leaf litter exhibited lower toxicity than fresh plant material and maize-fed arthropods. This suggests that nutritional quality of food and degradation of Cry proteins may influence toxicity to insects. When soil was spiked with Cry3Bb1, the Bt protein was highly adsorbed and retained its full biological activity. Because toxicity of Cry proteins contained in different matrices cannot always be determined from ELISA values alone, sensitive insect bioassays can improve hazard and exposure assessments in environmental risk assessment of Bt crops.