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.     

Adult dispersal of Ostrinia nubilalis Hübner (Lepidoptera: Crambidae) and its implications for resistance management in Bt-maize

Abstract:  Dispersal of European corn borer, Ostrinia nubilalis Hübner was examined by release and recapture of the dye marked adults and by capture of the feral adults in and around the large 50 ha center pivot irrigated fields of Bacillus thuringiensis (Bt) maize. Pheromone and black light traps were used to catch the adults. In 1999, 15 094 marked males and 7993 marked females were released, and in 2001, 13 942 marked males and 9977 marked females were released. In 1999, maximum mean recapture beyond the release point was 1.95 and 1.67% for males and females, but in 2001, the recapture rate was 9.97 and 4.37% for males and females. Few males (3.8%) and females (2.07%) were recaptured in neighbourhood maize fields. An exponential decay function explained recapture of marked adults across the dispersal distance. More than 90% of marked adults were recaptured within 300 m of the release point. Large numbers of feral adults were captured throughout the study fields. Feral adult dispersal could be fitted to a linear model. Virgin females (20% marked and 8% feral) were captured throughout the study fields. The recapture of marked insects suggests that the dispersal was limited. However, capture of feral adults throughout Bt-maize fields indicate that the actual dispersal may be more extensive than indicated by recapture of marked adults. Potential refuge sources for the feral adults were 587–1387 m from the edge of the study fields. It is not clear if the dispersal recorded in this study is extensive enough to support the current resistance management strategy for corn borers. There appears to be some dispersal of corn borers from the non-transgenic 'refuge' fields into the transgenic fields that allows some genetic mixing of the two populations.     

Population density of Diabrotica virgifera virgifera LeConte beetles in Serbian first year and continuous maize fields

A 5‐year field survey examined western corn rootworm (WCR) (Diabrotica virgifera virgifera LeConte) beetle density in Serbia from 2002 to 2006. First‐, second‐, third‐, fourth‐ and fifth‐year maize fields were sampled; they represented 64.61%, 21.66%, 9.45%, 3.53% and 0.75% of all sampled fields respectively. Results showed that the mean WCR beetle population density from 794 maize fields differed depending on cropping history. Minimum mean WCR/trap/day was 0.0 in the first‐year maize fields in 2002 and 2006. Maximum mean WCR/trap/day was registered in the fourth‐year and the fifth‐year maize fields (27.8 and 21.2 respectively). Mean population density of WCR adults increased with the number of years of continuous maize from 1.17, 4.61, 6.41, 10.30 up to 13.53 WCR/trap/day for first‐fifth‐year maize fields respectively. Mean WCR/trap/day ± SE exceeded the economic population threshold of >6 WCR/trap/day in third‐year continuous maize fields. Out of 794 maize fields, 697 (87.78%) registered a mean population density below the <6 beetles/trap/day threshold. In only 97 fields was WCR population density >6 beetles/trap/day, a finding that predicts a risk of economic damage to a subsequent maize planting. These data are representative of the Serbian situation from 2002 to 2006; they indicate that WCR are well dispersed across commercial maize fields in Serbia. These results provide new insight into the current low WCR population densities in maize fields managed by crop rotation, a finding that can help in creating long‐term management strategy.     

Dispersal and spatial distribution of western corn rootworm larvae in relation to root phenology

• 1 Despite the increasing economic importance of root feeding pests such as the western corn rootworm (WCR) Diabrotica virgifera virgifera, basic parameters about their below ground biology are only partly understood. The present study investigated the dispersal and distribution of WCR larvae in the maize root system during their development at two growth stages of maize (BBCH 13–14 and BBCH 17–18).
• 2 Dispersal of the WCR larvae increased as they developed; the larvae moved off their original place of emergence and into deeper soil layers. Overall, changes in the horizontal distribution of the larvae were more extensive than changes in the vertical distribution.
• 3 The spatial analysis of distance indices revealed that the larvae had an aggregative distribution throughout their development. The feeding site of larvae in the root system was determined by the stage of larval development. Initially, WCR larvae started feeding in close proximity to their emergence location and moved to more developed root tissue towards the end of their development.
• 4 Differences in root phenology mainly influenced the distribution of the larvae at the end of their development, when larvae exhibited increased vertical movement at a later growth stage of maize.
• 5 The mechanisms of these distributional changes and the implications for the management of WCR larvae are discussed, especially with regard to chemical control, because fewer larvae are expected to be targeted at a later growth stage of maize.

     

Predicted effect of climate change on the invasibility and distribution of the Western corn root‐worm

• 1 Insect pests, biological invasions and climate change are considered to represent major threats to biodiversity, ecosystem functioning, agriculture and forestry. Deriving hypothesis of contemporary and/or future potential distributions of insect pests and invasive species is becoming an important tool for predicting the spatial structure of potential threats.
• 2 The western corn rootworm (WCR) Diabrotica virgifera virgifera LeConte is a pest of maize in North America that has invaded Europe in recent years, resulting in economic costs in terms of maize yields in both continents. The present study aimed to estimate the dynamics of potential areas of invasion by the WCR under a climate change scenario in the Northern Hemisphere. The areas at risk under this scenario were assessed by comparing, using complementary approaches, the spatial projections of current and future areas of climatic favourability of the WCR. Spatial hypothesis were generated with respect to the presence records in the native range of the WCR and physiological thresholds from previous empirical studies.
• 3 We used a previously developed protocol specifically designed to estimate the climatic favourability of the WCR. We selected the most biologically relevant climatic predictors and then used multidimensional envelope (MDE) and Mahalanobis distances (MD) approaches to derive potential distributions for current and future climatic conditions.
• 4 The results obtained showed a northward advancement of the upper physiological limit as a result of climate change, which might increase the strength of outbreaks at higher latitudes. In addition, both MDE and MD outputs predict the stability of climatic favourability for the WCR in the core of the already invaded area in Europe, which suggests that this zone would continue to experience damage from this pest in Europe.

     

Performance of irradiated Teia anartoides (Lepidoptera: Lymantriidae) in urban Auckland, New Zealand

The Australian moth Teia anartoides Walker has been the target of a major eradication program in Auckland, New Zealand. Information on cold torpor and dispersal was needed to help interpret catches of sterile and wild males in female-baited delta traps operated in a grid of up to 1,696 traps at 500-m spacings across the city. Laboratory experiments indicated male flight was enabled at temperatures above 17 degrees C (confirmed by field trapping of wild and recaptured moths). Male survival in the field or in field cages was determined to be limited to approximately 4 d. Sterilization of males for dispersal studies was achieved by exposing male pupae to either 160 or 100 Gy by using 1.25 MeV gamma rays from a Cobalt source, before release as fluorescent-dyed emerged adults. Dispersal was determined by recapture of males in the trapping grid of 1,696 delta traps baited with virgin female moths and placed at spacings of 50-500 m. Irradiated sterile males dispersed up to a maximum recorded distance of 4,500 m (160 Gy) and 10,000 m (100 Gy). At 100 Gy, the median dispersal distance was 300 m, with 90% of males dispersing 1,600 m or less.     

Study of Aedes albopictus dispersal in Rome,Italy, using sticky traps in mark–release–recapture experiments

We report the results of three mark–release–recapture experiments carried out in an urban area in Rome, Italy, to study the active dispersal of Aedes albopictus (Diptera: Culicidae). The 4.3% recapture rate obtained supports the use of sticky traps in MRR experiments to study the dispersal of Ae. albopictus females. Most fluorescent dust‐marked females were recaptured at the gravid stage at 50–200 m from the release sites during the first 9 days after release. The average of daily‐MDTs (Mean Distance Traveled) was 119 m and the maximum observed distance travelled ranged from 199 m to 290 m in the three replicates. These data provide the first information about the dispersal of Ae. albopictus in a temperate European area and appear to be consistent with the few data available on this subject from other urban areas, where dispersal was constrained by physical barriers. Although caution should be taken in generalizing these results, they should be considered when planning control activities in urban areas in Italy, as well as in other European countries. This is particularly relevant if control is intended to interrupt pathogen transmission in cases of possible arbovirus epidemics, such as the Chikungunya outbreak that occurred in Ravenna, Italy in 2007.     

Short-range dispersal of recently emerged males and females of Bactrocera tryoni (Froggatt) (Diptera: Tephritidae) monitored by sticky sphere traps baited with protein and Lynfield traps baited with cue-lure

Abstract  Dispersal of immature male and female Queensland fruit fly, Bactrocera tryoni (Froggatt) (Diptera: Tephritidae), was assessed over a period of 1 week from a single release point on three separate occasions using an array of Lynfield traps baited with cue-lure and odouriferous yellow or black sticky spheres baited with food lure (protein autolysate). Lynfield traps recaptured males; yellow or black spheres recaptured both sexes in approximately equal proportions, although at a much lower rate. As a percentage of the recapture rate for males by Lynfield traps, the mean recapture rate for yellow spheres ranged from 1.0% to 7.5% for males and 0.7% to 4.0% for females, whereas the recapture rates for black spheres ranged from 0.4% to 3.6% and 0.6% to 1.8%, respectively. The rate of recapture of sterile male flies was greater than that of unsterilised flies; this may have been due to a faster maturation rate in sterile males or because a greater proportion of them remained within the trap array rather than dispersing. There was no significant trend in recapture rate with distance from the release point to the edge of the array (88 m), except in the case of females on sticky traps where no trend was detected between 19 and 88 m. These results lend support to assumptions made about the distribution of males and females with respect to the minimum breeding density of fruit fly propagules invading a fly-free zone, and the method chosen to distribute sterile B. tryoni for the sterile insect technique.     

Dispersal ability of marked,irradiated olive fruit flies [Bactrocera oleae (Rossi) (Diptera: Tephritidae)] in arid regions

The dispersal of marked, irradiated olive fruit flies originating from a hybrid laboratory strain was studied in an olive groove located in the arid regions of southern Israel. Release–recapture experiments (eight in total) were conducted throughout a period of 5 months (July–December 2008). In each experiment, ca. 5000 flies were released. Recapture of flies was conducted using a grid of 30 yellow sticky traps set in expanding semicircles from the centre of release. Service of traps was conducted 3 and 15 days after the release. Fly quality and adult food type (only sucrose and protein + sucrose) before release was also investigated. Results point at an average dispersal distance of marked, irradiated olive flies of ca. 50 m. Pre‐release adult diet did not affect dispersal ability. Fly recovery averaged ca. 3.5% during summer and ca. 1.5% during autumn. Most of the recovery concentrated during the first 3 days after releases, suggesting low survival of the released flies afterwards. As inferred from circular statistics, direction of dispersal was non‐random with a significant directionality to the north‐west. Results are discussed in view of environmental temperatures and wind direction.     

Small-scale dispersal of the European corn borer and its relevance for resistance management in Bt maize

The small-scale dispersal of the European corn borer (ECB) was studied in a release–recapture experiment using reared dye-marked adults. Thereby, six light trap cages were set up across two maize fields at 50-m intervals. In total, 736 marked ECBs were released, of which 10.2% were recaptured together with 212 unmarked naturally occurring adults after a period of 48 h. All marked–released individuals left the release point, with a mean dispersal distance of 195 m. Eighty-two per cent of the recaptured ECBs moved to the second maize field across a ditch and associated shrubs. The spatial and temporal patterns of incidence of naturally occurring ECBs in the traps were consistent with those of the marked moths and showed an inhomogeneous distribution. There was a highly significant relationship between male and female densities in the cages. No ECBs were caught during a period of adverse weather conditions. Dispersal distances may be influenced by plant size, weather conditions during the flight, pheromonal patterns in the field and the timing of the flight.     

Seasonal flight activity by the Asian citrus psyllid in east central Florida

The Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psyllidae), is an important invasive citrus pest in the USA because it vectors a bacterium responsible for huanglongbing, a devastating disease of citrus. Information was lacking on seasonal aspects of flight activity by D. citri, which could have ramifications on psyllid management as well as our understanding of epidemiology of the disease. Of interest from a pest management standpoint would be whether D. citri regularly disperses to or away from citrus on a predictable schedule. In research presented here, seasonal flight activity by D. citri was investigated using yellow sticky traps deployed in citrus trees and in fallow areas adjacent to citrus. Results indicated that flight activity by both male and female D. citri away from citrus can occur at any time of the year with consistent dispersal activity during the spring. The research further indicated citrus is continually subject to infestation by immigrating adults and that there is no time during the year that a citrus grower could be assured immigration would not occur. Growers should be aware that adult dispersal occurs regularly during spring and they should time management tactics accordingly. Adult flight activity 2 m from a citrus tree was more pronounced at 1 m above ground than at 2 or 3 m high. At distances of 8–60 m from trees, numbers of adults on traps were similar among the three heights. Males and females were similar with respect to seasonal flight activity. Numbers of adults captured on traps distant from citrus were not correlated with wind speed, sunlight, or air temperature, but there was some evidence that relative humidity influenced flight activity. Although the D. citri life cycle is dependent on flush, data from these studies did not confirm that psyllid dispersal from citrus consistently increases as citrus flush abundance decreases.     

How effective are buffer zones in managing invasive beavers in Patagonia? A simulation study

In an age of invasions, it is critical to design and test management strategies to more efficiently control foreign species. Spatially explicit individual based models (SEIBMs) are a powerful tool to explore different management scenarios to control invaders, but we rarely have enough data to parameterize these models, particularly for relatively long-lived species. Here we take advantage of our previous work estimating demographic rates of invasive beavers in Patagonia, and develop an SEIBM to model the spread of beavers in Patagonia. We used our SEIBM both to estimate dispersal distances by fitting their observed rate of spread and to test how placing a buffer zone (a longitudinal strip of land perpendicular to the direction of spread within which a fraction of beavers are culled) beyond the invasion front would work as a control strategy. Specifically, we explored six different scenarios with two different culling rates and two buffer zone widths. We found that beavers in Patagonia must disperse long distances on average to account for the observed rate of spread, and thus our model predicts that a 100 km buffer zone will be needed to slow (but likely not halt) the spread of beavers. Interestingly, culling a higher proportion of beavers within a 100 km buffer zone (90 vs. 60%) did not improve buffer zone performance. Our study shows that wide buffer zones can slow (but likely not halt) continental spread of beavers in Patagonia and potentially pave the way for beaver eradication.     

Adult movements of newly introduced alien Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae) from non-host habitats

Mark-release-recapture experiments were undertaken in order to investigate the movement of adult Diabrotica virgifera virgifera LeConte from accidental introduction points towards suitable habitats, such as its host plant, Zea mays L. In Hungary in 2003 and 2004, nine mark-release-recapture experiments were carried out in a grass steppe area and lucerne field, in which two small maize fields (10x10 m) had been planted 300 m distant from the central release point. After each release of 5500 to 6000 marked D. v. virgifera, beetle recaptures were recorded three times using non-baited yellow sticky traps placed on 30, 105, 205 and 305 m radii around the release point. In seven out of 15 recapture periods (47%), beetle populations showed no directional movements, and their movements towards any particular habitat cannot be predicted. During five recapture periods (33%), beetle populations showed a uni-directional movement, and in three cases (20%) a bi-directional movement was observed. In 10 out of 15 recapture periods (67%), the released populations moved in a direction that was comparable with the mean wind direction during these periods; thus, beetle movements were slightly correlated with wind direction. On average over sites and years, beetles were not preferentially moving towards the two small maize fields (located 300 m from the release point) compared to other directions. However, beetles moved significantly more frequently in the direction of naturally-occurring maize fields within a radius of 1500 m than towards other habitats. Beetles stayed more frequently within flowering lucerne fields out to a radius of 300 and 600 m than in non-flowering lucerne or other habitats. On average, 2.8% (SD 3.2) of all recaptured beetles arrived in one of the two small maize fields located 300 m from their release point indicating that there is a high risk of a founder population establishing. Habitat management cannot be suggested as a means of preventing the beetle's initial dispersal because movement was usually non-directional, and alternative food plants were used prior to reaching maize.     

Olfactory responses of the omnivorous generalist predator Dicyphus hesperus to plant and prey odours

This paper describes a method for studying the neighbourhood (dispersal) movement of pest insects that overcomes the major problems associated with release/recapture experiments. The method has been developed using the carrot fly, Psila rosae (Fab.) (Diptera: Psilidae), as the experimental insect. It involves building up a large population of insects in an area free of other host plants, and then, as the insects disperse in the spring, monitoring the fall‐off in numbers of insects with increasing distance. Estimates of the fall‐off in numbers of the carrot fly were obtained by using sticky traps to monitor changes in fly numbers in 11 small plots of carrots drilled 130–1300 m away from the site at which the flies emerged (emergence site) in the spring. A strong linear relationship (r² = 0.96) was obtained between the log₁₀ numbers of flies caught in each plot and the log₁₀ distance the plot was from the emergence site. Few flies were caught more than 1 km from the emergence site. A linear relationship (r² = 0.86) was also obtained between the date when 50% of the flies were caught in each plot and the distance the plot was from the emergence site. The date of 50% capture was delayed by 1 day for each 100 m the given plot was away from the emergence site. This suggests that when carrot flies move to find new crops, the population moves about 100 m day^?1. About one million flies would have to be released in conventional release/recapture experiments to obtain data as robust as those collected using the current method. The major breakthrough of this method is that dispersal can be estimated for an insect species that, although a major pest of field crops of carrots and parsnips, is exceptionally difficult to rear, even in relatively small numbers, under controlled‐environment conditions.     

Laboratory and field response of the pollen beetle, Meligethes aeneus, to the odour of oilseed rape

Abstract. The behavioural response of adults of the pollen beetle, Meligethes aeneus F. (Coleoptera: Nitidulidae), to the odour of one of their host-plants, oilseed rape ( Brassica napus L.), was observed in the laboratory using a fourarmed airflow olfactometer, and under semi-natural conditions using a markrelease–recapture technique. Oilseed rape leaf and flower odour was attractive to pollen beetles in the olfactometer and they dispersed upwind from the centre of a circular array (radius 20 m) of yellow water traps, baited with extracts of oilseed rape leaves or flowers. The dispersal of pollen beetles in the absence of oilseed rape odour was predominantly downwind and crosswind. The percentage recapture of pollen beetles was significantly greater in traps baited with rape flower extracts than leaf extracts. Pollen beetles can use odour-mediated upwind anemotaxis to locate oilseed rape plants from distances of at least 20 m over open ground.     

UV‐absorbing films and nets affect the dispersal of western flower thrips,Frankliniella occidentalis (Thysanoptera: Thripidae)

UV‐absorbing films and nets are frequently used as covering materials for netted greenhouses and film tunnels in protected cultivation systems. This study explored the effects of such materials on the dispersal behaviour of western flower thrips (WFT), Frankliniella occidentalis, in flight cages under greenhouse conditions with additional artificial UV‐A light sources. The study involved release–recapture experiments in choice and no‐choice layouts. Different trapping methods were compared (blue sticky cards, plants and transparent cards) for recapture of thrips. In choice experiments, insects were released from a black box compartment between two tunnels covered with either UV‐transmitting or UV‐absorbing materials. A significantly higher proportion of (82–98%) WFT was recaptured in UV‐transmitting tunnels compared with UV‐absorbing tunnels. In no‐choice experiments, WFT were found to infiltrate the tunnels at different rates depending on the trap type used and experimental layout. In small‐scale dispersal experiments using blue sticky cards and plants as traps, infiltration was not significantly different between UV‐absorbing and UV‐transmitting tunnels, whereas when using transparent cards, WFT penetrated further into the UV‐transmitting plastic film tunnels. In larger‐scale dispersal experiments, plants or blue sticky cards were arranged in concentric circles around a source plant at the release point. Dispersal was found to differ depending on the method of release, but WFT tended to exhibit reduced dispersal from source plants under UV‐deficient conditions. In conclusion, our data support the hypothesis that manipulation of spectral light properties using UV‐absorbing cladding materials for protected crop stands interferes with the orientation and host finding of WFT, resulting in reduced dispersal into and within plant stands in UV‐deficient environments.     

Effects of adult emergence timing on susceptibility and fitness of Cry3Bb1‐resistant western corn rootworms

Field‐evolved resistance by the western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte to the Cry3Bb1 trait expressed in maize, has been documented in areas of Nebraska USA. Currently, only limited information is available on life‐history traits of Cry3Bb1‐resistant field populations. Therefore, the Gassmann on‐plant bioassay was used to investigate the potential variability among four Cry3Bb1‐resistant WCR field collections made in 2011–2012 by focusing on the key parameters: larval survival, developmental stage and weight with specific emphasis on the impact of adult emergence timing on these parameters in subsequent progeny. Key results: In three of four collections, the susceptibility of larval progeny from adults that emerged early or late within a generation from Cry3Bb1 plants was similar. Each of the three collections exhibited complete resistance; that is, survival on Cry3Bb1 plants was greater or equal to survival on non‐Bt isoline plants. Bioassays from an additional field collection from one site 2 years (2013) after the original collection (2011) (both from Cry3Bb1 maize) indicated that resistance to Cry3Bb1 was maintained over time at the site despite Bt trait rotation in 2012. In general, comparative WCR life‐history parameter data from Cry3Bb1 and isoline maize indicate that fitness of field collections exhibiting complete resistance was similar on each hybrid. The mean proportion of larvae in third instar and mean weight of larvae recovered in bioassays from progeny of early‐ and late‐emerged adults was not significantly affected by emergence period. This suggests that delays in development and associated mean adult emergence commonly observed in populations that are susceptible to Cry3Bb1 may become smaller as populations become resistant to Cry3Bb1. Results from this article will inform Cry3Bb1 resistance mitigation efforts and contribute to the development of sustainable WCR management programmes.     

Volatile semiochemical impact on trapping and distribution in maize of northern and western corn rootworm beetles (Coleoptera: Chrysomelidae)

Abstract 1 Field studies evaluated plant attractants and analogues as tools to move corn rootworm beetles (Diabrotica spp.) into areas to be treated with toxic baits for population suppression via mass removal/annihilation of reproductive adults. 2 When dispensed from sticky traps in maize, 2‐phenyl‐1‐ethylamine and 2‐phenyl‐1‐ethanol captured more northern corn rootworm, Diabrotica barberi, than did 4‐methoxyphenethanol. Only 2‐phenyl‐1‐ethanol attracted the western corn rootworm, Diabrotica virgifera virgifera, but not until maize matured beyond milk stage. 3 Attraction of D. barberi to the amine, alone or blended with 2‐phenyl‐1‐ethanol, occurred before and after maize flowered but not during intervening silk or blister stages. Attraction recurred during early milk stage at or before 50% emergence of adult female D. barberi or D. v. virgifera, respectively, and before populations declined for the season. 4 Synergistic interaction of 2‐phenyl‐1‐ethylamine with 2‐phenyl‐1‐ethanol in attracting D. barberi females did not occur until maize matured to late milk stage. 5 The amine‐alcohol blend (0.44 point sources m^?2) doubled the density of D. barberi but not D. v. virgifera when applied to small plots within mostly milk‐stage or younger maize. Traps without bait within attractant‐treated plots captured more female, but not male, D. barberi than did traps in untreated control plots, hinting that females accounted for most of the observed increase in beetle density. 6 The results suggest that attractants can be used despite phenological limitations to concentrate preovipositional females within field areas and thus to complement a variety of corn rootworm control strategies.     

The influence of weather and geographical conditions on flight dynamics of WCR adults

Since the appearance of western corn rootworm (Diabrotica virgifera virgifera Le Conte) (Coleoptera: Chrysometidae) in Romania, many researchers have been made, in more or less success. In this study we try to clarify the ecology of the species in order to predict its evolution and its potential area of distribution. In Romania, this species was signalled for the first time in 1996, in western part of country neighbouring with Hungary. This region is an important area for maize production for seed and silage. Together, the climatic conditions, altitude and their influence on species behaviour and distribution have become more apparent. Their habitat and survival strategies are strongly dependent on local weather patents and altitude. In order to investigate the potential impact of weather and altitude on pest populations, a clear understanding of the nature and characterization of pest is required. In general, most pest species are influenced by warm, rainfall and altitude. Taking into consideration our data from the years 2008 and 2009, we can emphasize a very serious influence of air temperature, rainfall and altitude on WCR flight dynamics in adults. Dry and warm conditions generally lead to increasing of insects' number. Our data shown positive correlations between air temperature (daily mean) and adults number captured on pheromone traps (daily mean), but the there are limits from which these become negative. The same trend was recorded in previous research period (2004-2006). The rainfall is an important factor that influences adults' dynamics in maize fields. Excessive rainfall leads to adults' number decreasing. Our daily observations showed a decreasing number of beetles while rainfall increases. Regarding the altitude, we observed a decreasing number of WCR adults at once the attitude increase. For capture of adults we used pheromone traps, in 3 replications (T1, T2 and T3) at difference altitude where maize was grown. Significant relationship of WCR flight dynamic with weather and geographical conditions were found. Activities were carried out under the PN-II-ID-PCE-2007-1/RO project.     

The distribution and abundance of Delphacidae (Homoptera) in central Argentina

A 3-year field study has been carried out on the distribution and abundance of Delphacidae in central Argentina. Insects were collected along a 300 km transect of seven equally spaced sampling sites. At each sampling station there was one sticky trap 6 m above the ground and five sticky traps 1.5 m above the ground. The sampling frequency was every 6 to 15 days during the spring and summer months and monthly during the rest of the year. Delphacodes kuscheli (vector of a local strain of the maize rough dwarf virus, MRDV-RC), Delphacodes haywardi, Delphacodes balboae, Toya spp., Dicranotropis nigricula and Sogatella kolophon meridiana were collected. Among them, D. kuscheli and Toya spp. comprised 67 and 26% of all the delphacid captured. Delphacodes kuscheli showed a geographical gradient in abundance, coincident with the land management gradient which showed a very heterogeneous landscape (in terms of crop species and land management) dedicated to grain production in the north-eastern part of the study area and a less heterogeneous landscape dedicated to cattle breeding (with large extensions covered with pastures where D. kuscheli reproduces and overwinters) in the south-west. Delphacodes kuscheli showed a high dispersal ability and synchronic dynamics, whereas Toya spp. showed a lower dispersal ability with less synchronic dynamics. The implications for the MRDV-RC transmission is discussed.