Lorenzo Furlan

The biology of Agriotes sordidus Illiger (Col., Elateridae)

Abstract:  This paper describes the life cycle, including adult behaviour, oviposition, larval and pupal development rate of Agriotes sordidus Illiger. Each larva passed through up to eight to 13 instars. The larval size range of each instar was defined. Larvae need live vegetable tissues to survive and grow, otherwise most die within 40 days. Resistance to starvation increases with the age of the larvae (last instars can survive up to 1 year without food at 20°C). Each instar passes through three phases: mandible hardening and darkening, feeding, pre‐moulting. The intense feeding (damaging plants) phase lasted <25% of the whole development time. They are poliphagous and the rate of larval development does not vary with host‐plant type (maize, alfalfa). Provided sufficient soil moisture and food are present, larval development rate strongly depends on soil temperature. The duration of each instar increased with the age of the larvae. No larval growth was observed below 9°C. Under laboratory conditions the average heat sum (above a base of 9°C) required for development from egg to adult was about 3900 DD. Similar results were found in the rearing cages and in the open field. At the latitudes of the regions where this study was carried out (northern Italy, Veneto between 45°34′00′′N and 45°42′00′′N and central‐south Italy, Molise, between 41°49′720′′N and 41°56′501′′N) the 6th instar (which normally is the first one passing 10 mm in length) is attained by September of the same oviposition year. Pupae can be found between the end of May and September mostly in the upper soil layer. Their transformation into adults took about 16 days at 25°C. Larvae of different stages overwintered by burrowing deep into the soil. Vertical migrations during the year are described: they depend mostly on soil temperatures from October to early spring. The adults overwintered and laid eggs in the subsequent spring. At lower latitudes or in warm seasons most of the population completed its life cycle (from egg to egg) in 24 months over three calendar years. At more northern latitudes, part (sometimes most) of the population completed the whole life cycle in about 36 months over four calendar years.

The ineffectiveness of insecticide seed coatings and planting‐time soil insecticides as Diabrotica virgifera virgifera LeConte population suppressors

Abstract:  The effect of any management strategy on pest population levels must be researched and determinations need to be made as to how that strategy might work based on the control objectives. In certain areas of Europe, the objective is to contain or eradicate the western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte, population. In order to evaluate the impact of insecticide seed coatings and/or planting‐time applications of insecticides as WCR population suppressors, plot trials and large field observations were carried out in Italy over a 5‐year period. Larval, pupal and adult densities, along with root damage ratings, were estimated at different locations. Data from these studies revealed that the number of WCR adults emerging from untreated plots did not differ from the number of beetles emerging from those treated with insecticides, whether as seed coating or in‐furrow applications. Both seed insecticide coatings (imidacloprid, fipronil, thiamethoxam, tefluthrin) and soil insecticides applied in‐furrow (chlorpyrifos, diazinon, tefluthrin) did not reduce the number of beetles emerging from monoculture fields, either in plot trials or large field observations. Observations in the USA had previously shown that soil insecticides applied at planting time partially protected basal roots from economic damage, but did not reduce corn rootworm populations. Similarly, in Europe, it has been demonstrated that not only the application of soil insecticides at planting time but also insecticide seed coatings have no role in the containment and/or eradication of WCR. Although insecticide seed coatings and soil insecticides applied in‐furrow may provide protection against economic damage to roots, these management strategies do not have an impact on WCR populations and therefore are useless in WCR containment and eradication programmes.

Identification of Sex Pheromone Composition of Click Beetle Agriotes brevis Candeze

Geranyl butyrate (GB) and (E,E)-farnesyl butyrate (FB) were identified in the pheromone gland extract of females of the click beetle, Agriotes brevis (Candeze) (Coleoptera: Elateridae) as the major sex pheromone components. Polyethylene vial dispensers containing 20–200 mg of a 1:1 mixture caught high numbers of beetles. Captures did not decrease even after 73 days of field exposure of dispensers. At sites where both Agriotes sputator L. and A. brevis were present, the above baits were selectively catching only A. brevis, despite the fact that GB is also the main pheromone component of A. sputator, suggesting that FB has a role in reproductive isolation. In the early part of the season, traps into which the insects could both crawl and fly captured more A. brevis than designs where the insects could only fly in. Trap design was not important later in the season. This indicates the need for future development of a trap suitable for use throughout the whole season.

New Sex Attractant Composition for the Click Beetle Agriotes proximus: Similarity to the Pheromone of Agriotes lineatus

While testing traps baited with a blend of geranyl octanoate and geranyl butanoate (pheromone components previously identified for Agriotes lineatus, Coleoptera, Elateridae) in Portugal and Bulgaria, large numbers of the closely related Agriotes proximus were captured. In the literature, two different compounds, (E,E)-farnesyl acetate and neryl isovalerate had previously been identified as pheromone components of A. proximus. Subsequent field tests, conducted in several European countries, revealed that A. proximus was weakly attracted to geranyl butanoate on its own, while A. lineatus was weakly attracted to geranyl octanoate on its own. However, the largest catches for both species were observed with a blend of both compounds. No A. proximus was caught in traps baited with the blend of (E,E)-farnesyl acetate and neryl isovalerate at any of the test sites. In electroantennographic studies, antennae of male A. proximus and A. lineatus both gave greater responses to geranyl butanoate than to geranyl octanoate, suggesting that the perception of these two compounds was similar for both species. A 1:1 blend of geranyl octanoate and geranyl butanoate can be used as a bait in traps for the detection and monitoring of both A. lineatus and A. proximus in many European countries.

Geranyl hexanoate attracting male click beetles Agriotes rufipalpis Brullé and Agriotes sordidus Illiger (Col., Elateridae)

Abstract:  In field screening tests in Hungary, traps baited with geranyl hexanoate captured males of the click beetle Agriotes rufipalpis Brullé, whereas in Italy males of Agriotes sordidus Illiger (Col., Elateridae) were captured. Geranyl hexanoate‐baited traps could be very useful in rationalizing the control of these pests. Such traps can give useful information without making expensive and time‐consuming samplings of the soil layers in search of larvae. Traps can be effective also in describing swarming patterns and identifying the peak of male activity, thus yielding an estimate of the level of adult populations, making it possible to forecast future outbreaks and to concentrate agronomic and chemical control strategies against the pests most effectively.

Agriotes proximus and A. lineatus (Coleoptera: Elateridae): a comparative study on the pheromone composition and cytochrome c oxidase subunit I gene sequence

The presence of geranyl octanoate, previously found in pheromone gland extracts of Agriotes lineatus females, was also demonstrated in gland extracts of A. proximus females. Similar to A. lineatus, geranyl butanoate was present only in trace amounts in A. proximus female gland extracts. In air entrainment samples of female A. lineatus and A. proximus beetles, the relative ratio of geranyl butanoate and geranyl octanoate was higher than that in gland extracts. In addition, comparison of a segment of the mitochondrial cytochrome c oxidase subunit I gene of feral specimens of A. lineatus and A. proximus showed >99% similarity. Both pheromone profile and nucleotide sequence analysis delineate close relationship between the investigated taxa and postulate taxonomic revision. Further studies on sympatric populations of A. lineatus and A. proximus are underway to investigate and better understand possible processes of species diversification.

Seasonal fluctuations in Agriotes spp. (Coleoptera: Elateridae) at two sites in Austria and the efficiency of bait trap designs for monitoring wireworm populations in the soil

Wireworms, the larvae of Agriotes spp. (Coleoptera: Elateridae), cause serious damage to a number of crops. To develop an effective management strategy, a reliable method of estimating the abundance of the Agriotes species is needed. This paper describes a trapping study of Agriotes in parts of Austria. Over two years, adult click beetles were monitored using YATLOR sex pheromone traps and wireworms were monitored using bait traps. Also, the efficiency of bait traps with different numbers of perforations was compared. In a location in Upper Austria, A. lineatus was by far the most common species and in a location in lower Austria, the majority of beetles caught were A. ustulatus. A. brevis was common in Upper Austria, but nearly absent in Lower Austria. There were large discrepancies between the species compositions of the adults and larvae caught, suggesting a low efficiency of the bait traps. More larvae were caught in bait traps with greater numbers of holes, but the difference was not statistically significant. Further improvements in bait traps or another sampling method will be needed to accurately estimate the density of wireworms.

Female Responses to Synthetic Pheromone and Plant Compounds in Agriotes brevis Candeze (Coleoptera: Elateridae)

Traps baited with synthetic pheromone components of Agriotes brevis [geranyl butanoate + (E,E)-farnesyl butanoate] captured significantly higher numbers of not only male, but also female beetles, compared to unbaited controls. Catches of both sexes showed a clear positive relationship with increasing doses. In electroantennogram tests, antennal responses of females and males to a number of known Agriotes pheromone components, identified from pheromone glands, showed a similar trend, with geranyl butanoate eliciting the strongest responses. This suggests that the female and male A. brevis antennae are similar with respect to the perception of pheromone compounds, and female beetles have the sensory capabilities to perceive the pheromone components which they produce. Addition of the plant-derived compounds (Z)-3-hexenyl acetate, methyl benzoate, (Z)-3-hexenol and methyl salicylate (identified earlier from foliage as attractive for A. brevis) to the synthetic pheromone significantly increased catches. All the above results suggest that geranyl butanoate and (E,E)-farnesyl butanoate are constituents of an aggregation pheromone of A. brevis, in contrast to the general view of click beetle pheromones being “classical” sex pheromones. These findings could be useful for more precise monitoring and forecasting of damage, based on female catches.

European corn borer (Ostrinia nubilalis Hbn., Lepidoptera: Crambidae): comparing the performance of a new bisexual lure with that of synthetic sex pheromone in five countries.

BACKGROUND Phenylacetaldehyde is a flower volatile and attractant for among others the European corn borer Ostrinia nubilalis. The addition of 4-methoxyphenethyl alcohol has recently been reported to increase O. nubilalis catches four to five times, yielding a bisexual lure for the species. RESULTS The bisexual lure significantly outperformed synthetic pheromone lures of O. nubilalis at 11 out of 13 experiments conducted in Bulgaria, Hungary, Italy, Slovenia and Turkey. CONCLUSION The bisexual lure will provide growers with a new and efficient method for detection and monitoring of O. nubilalis.