Impact of Chemical Insecticide Application on Beneficial Insects in Maize.

The European corn borer (ECB) (Ostrinia nubilalis Hübner) and to a lesser extent the western corn rootworm (Diabrotica virgifera virgifera LeConte) are a threat to maize in the Po Valley (Northern Italy), and their control can require insecticide applications. The results of a study to evaluate the effects of insecticide sprays on the beneficial insect Trichogramma brassicae (Hymenoptera: Trichogrammatidae) and aphid predators are reported. A three-year research project was carried out in two Study Areas, in Lombardy. In area 1, crop rotation was a common practice, while in area 2 repeated maize crop was practiced. The natural trend of ECB egg masses attacked by T. brassicae was affected and parasitism rates were reduced as a result of insecticide exposure (chlorpyriphos methyl, cypermethrin, alphacypermethrine). Repeated maize crop and insecticides spraying increased the abundance of the aphid population and negatively affected the aphid predator community, which mainly included ladybirds, hoverflies, true bugs and lacewings. The predator community was dominated by hoverflies in sprayed fields managed according to repeated maize crop protocols, whereas ladybirds and Orius spp. dominated in maize fields managed according to crop rotation protocols. Crop rotation protocols help to prevent ECB outbreaks; when the risk of exceeding the economic threshold limit is high, and this may be the case when maize is cultivated for seeds or for horticultural crops such as sweet corn, inundative release of T. brassicae and/or microbial control (i.e., use of Bacillus thuringiensis preparations) can integrate natural biocontrol, and provide a valuable alternative to chemical insecticides.

Mating Disruption of Helicoverpa armigera (Lepidoptera: Noctuidae) on Processing Tomato: First Applications in Northern Italy.

Helicoverpa armigera is a polyphagous and globally distributed pest. In Italy, this species causes severe damage on processing tomato. We compared the efficacy of mating disruption with a standard integrated pest management strategy (IPM) in a two-year experiment carried out in Northern Italy. Mating disruption registered a very high suppression of male captures (>95%) in both growing seasons. Geostatistical analysis of trap catches was shown to be a useful tool to estimate the efficacy of the technique through representation of the spatial pattern of captures. Lower fruit damage was recorded in mating disruption than in the untreated control plots, with a variable efficacy depending on season and sampling date. Mating disruption showed a higher efficacy than standard IPM in controlling H. armigera infestation in the second season experiment. Mating disruption showed the potential to optimize the H. armigera control. Geostatistical maps were suitable to draw the pheromone drift out of the pheromone-treated area in order to evaluate the efficacy of the technique and to detect the weak points in a pheromone treated field. Mating disruption and standard IPM against H. armigera were demonstrated to be only partially effective in comparison with the untreated plots because both strategies were not able to fully avoid fruit damage.

Interactions between the Multicolored Asian Lady Beetle Harmonia axyridis and the Parasitoid Dinocampus coccinellae.

Harmonia axyridis (Pallas) has been introduced either intentionally or accidentally in different areas outside its native range, where it is often regarded as invasive. Dinocampus coccinellae (Schrank) has been recorded to parasitize H. axyridis in the field, both in the native and introduced areas, Italy included. The percent of parasitism found in our field investigation was low (four percent). The effect of exposure time of H. axyridis to D. coccinellae and the impact of parasitization on host longevity, oviposition capacity and egg fertility were evaluated in the laboratory. The acceptance and suitability of H. axyridis as host for D. coccinellae were then studied, in comparison with the native coccinellid Adalia bipunctata (L.), which shares the same ecological niche. The effects of parasitization on female longevity and reproduction capacity in the exotic vs. the indigenous lady beetle were also investigated. The overall results showed that D. coccinellae negatively affected the fitness of H. axyridis, more than that of A. bipunctata. The parasitoid may thus play a marginal role in controlling the populations of the Asian lady beetle, without representing a threat to A. bipunctata.

Chronic toxicity and physiological changes induced in the honey bee by the exposure to fipronil and Bacillus thuringiensis spores alone or combined.

In the agricultural environment, honey bees may be exposed to combinations of pesticides. Until now, the effects of these combinations on honey bee health have been poorly investigated. In this study, we assessed the impacts of biological and chemical insecticides, combining low dietary concentrations of Bacillus thuringiensis (Bt) spores (100 and 1000µg/L) with the chemical insecticide fipronil (1µg/L). In order to assess the possible effects of Cry toxins, the Bt kurstaki strain (Btk) was compared with a Bt strain devoid of toxin-encoding plasmids (Bt Cry(-)). The oral exposure to fipronil and Bt spores from both strains for 10 days did not elicit significant effects on the feeding behavior and survival after 25 days. Local and systemic physiological effects were investigated by measuring the activities of enzymes involved in the intermediary and detoxication metabolisms at two sampling dates (day 10 and day 20). Attention was focused on head and midgut glutathione-S-transferase (GST), midgut alkaline phosphatase (ALP), abdomen glyceraldehyde-3-phosphate dehydrogenase (GAPD) and glucose-6-phosphate dehydrogenase (G6PD). We found that Bt Cry(-) and Btk spores induced physiological modifications by differentially modulating enzyme activities. Fipronil influenced the enzyme activities differently at days 10 and 20 and, when combined with Bt spores, elicited modulations of some spore-induced physiological responses. These results show that an apparent absence of toxicity may hide physiological disruptions that could be potentially damaging for the bees, especially in the case of combined exposures to other environmental stressors.

Macrocyclops albidus (Copepoda: cyclopidae) for the Biocontrol of Aedes albopictus and Culex pipiens in Italy.

The aim of our study was to assess the potential of Macrocyclops albidus as a biological control agent against the 1st and 2nd instars of Culex pipiens and Aedes albopictus. Under laboratory conditions of prey saturation (50 1st instars/copepod), an average of 58.98% of Cx. pipiens and 54.99% of Ae. albopictus larvae were killed by 1 copepod in 24 h. Trials run in big drums containing 200 liters of water showed that the M. albidus population, inoculated in April, efficiently controlled the mosquito population for the entire season. The predator was particularly effective against Ae. albopictus, as only 2 larvae of this species were found in the treated drums, compared to 814 larvae in untreated control drums throughout the study period. No difference was observed in the control efficacy between the 2 initial densities of copepods used. The reduction in Ae. albopictus density in the drums with 100 and 500 M. albidus with respect to the control drums was 99.90 ± 0.35% and 100.0 ± 0.0%, respectively. For Cx. pipiens, the reduction in density was 88.69 ± 13.51% and 84.65% in drums inoculated with 100 and 500 copepods, respectively. Macrocyclops albidus populations survived through the winter and continued to keep the mosquito population under control during the 2008 season. The M. albidus population developed very well both in drums placed in sunny and shaded areas and proved to be tolerant to both high (summer) and low (winter) temperatures. Trials performed on M. albidus survival in catch basins showed that after a few weeks, the copepod population dramatically decreased and subsequently disappeared. The main problem for copepod survival in catch basins seemed to be the low oxygen tension and accumulation of toxic substances, rather than copepods being flushed out in heavy rainfall episodes. During the period when copepods were present, they maintained the mosquito population under control; their partial disappearance from the catch basins, however, would require more recolonization intervention to maintain mosquito control during the season.

Duration of prepupal summer dormancy regulates synchronization of adult diapause with winter temperatures in bees of the genus Osmia.

Osmia (Osmia) bees are strictly univoltine and winter as diapausing adults. In these species, the timing of adult eclosion with the onset of wintering conditions is critical, because adults exposed to long pre-wintering periods show increased lipid loss and winter mortality. Populations from warm areas fly in February-March and are exposed to longer growth seasons than populations from colder areas, which fly in April-May. Given their inability to produce an extra generation, early-flying populations should develop more slowly than late-flying populations and thus avoid the negative consequences of long pre-wintering periods. In this study we compare the development under natural and laboratory conditions of phenologically-distinct populations in two Osmia species. Early-flying populations took ∼2 months longer to develop than late-flying populations. Differences between populations in larval and pupal period duration were very small, whereas the prepupal period was much longer in early-flying populations. In contrast to the larval and pupal stages, the prepupal stage showed a non-linear response to temperature, was strongly affected by thermoperiod, and exhibited minimum respiration rates. Coupled with other lines of evidence, these results suggest that the prepupal period in Osmia corresponds to a summer diapause, and its duration may be under local selection to synchronize adult eclosion with the onset of winter temperatures. We discuss the implications of our results relative to current expectations of global warming.

The long summer: pre-wintering temperatures affect metabolic expenditure and winter survival in a solitary bee.

The impact of climate change on insect populations depends on specific life cycle traits and physiological adaptations. The solitary bee Osmia lignaria winters as a pre-emergent adult, and requires a period of cold temperature for winter diapause completion. It is a univoltine species, and diapause induction does not depend on photoperiod. To understand the potential effects of longer summers on O. lignaria populations, we exposed individuals to three treatments simulating early, mid and late winter arrivals, and measured respiration rates, metabolic expenditure, weight loss, fat body depletion, lipid levels and winter mortality. The early-winter treatment disrupted diapause development, but had no apparent negative effects on fitness. In contrast, late-winter bees had a greater energetic expenditure (1.5-fold), weight (1.4-fold) and lipid (2-fold) loss, greater fat body depletion, and a 19% increase in mortality compared to mid-winter bees. We also monitored adult eclosion and arrival of winter temperatures under natural conditions in four years. We found a positive correlation between mean degree-day accumulation during pre-wintering (a measure of asynchrony between adult eclosion and winter arrival) and yearly winter mortality. Individually, bees experiencing greater degree-day accumulations exhibited reduced post-winter longevity. Timing of adult eclosion in O. lignaria is dependent on the duration of the prepupal period, which occurs in mid-summer, is also diapause-mediated, and is longer in populations from southerly latitudes. In a global warming scenario, we expect long summer diapause phenotypes to replace short summer diapause phenotypes, effectively maintaining short pre-wintering periods in spite of delayed winter arrivals.

Dispersal and survival of Aedes albopictus (Diptera: Culicidae) males in Italian urban areas and significance for sterile insect technique application.

The dispersal and survival of laboratory-reared Aedes albopictus Skuse males were investigated during the summer of 2007 in three Northern Italy urban localities by mark-release-recapture techniques. Two marking methods were compared: one group of males was dusted with fluorescent pigments on the body (FP), and the other group was obtained from a strain whose natural infection of Wolbachia had been removed (WB0). FP- and WB0-marked males were released as adults and pupae, respectively, in one fixed station at each locality. Recaptures were performed by skilled technicians, within a radius of 350 m from the release site, on days 4, 5, and 7 after the release, and the males were collected while flying around the technician's body or in swarms. Recapture rates ranged from 0.63 to 4.72% for FP males and from 2.39 to 11.05% for WB0 males. The mean distance traveled for WB0 males was significantly higher than for FP males; no difference was observed between the dispersal distance measured for the males recaptured on human host versus males recaptured while swarming. No further increase of the dispersal occurred during the postrelease period investigated (from day 4 to day 7 after release). The mean survival rate at the release was 0.51 for FP-marked males and 0.81 for WB0 males. The data obtained are discussed for their significance in planning sterile insect technique programs against Ae. albopictus.

Tolerance thresholds for Aedes albopictus and Aedes caspius in Italian urban areas.

With nuisance mosquito species, the goal of integrated pest management is to keep mosquito density below a tolerance level that is often set by economic, ecological, and political factors. This study compares actual human annoyance, as measured by a phone survey, with several measures of mosquito abundance, in order to determine a threshold that is both relevant and practical. The efficiency of CO2-baited traps, container index (CI), and oviposition traps for monitoring Aedes albopictus, and CO2-baited traps for monitoring Aedes caspius, was evaluated. CO2-baited traps were confirmed to be of low efficiency in Ae. albopictus collection, while correlation matrices showed a good relationship between CI and the number of eggs collected (R = 0.91), and between number of eggs and phone-survey nuisance level estimates (R = 0.88). Correlation between CI and phone-survey nuisance levels was slightly lower (R = 0.78). We found a close relationship between the nuisance level declared by residents and mosquito captures obtained with CO2-baited traps (Ae. caspius) and ovitraps (Ae. albopictus). An equation is presented to estimate annoyance according to dwelling characteristics and to the presence of children in the family.