Stefano Maini

On intra-guild predation and cannibalism in Harmonia axyridis (Pallas) and Adalia bipunctata L. (Coleoptera: Coccinellidae)

Abstract Interspecific competition between the exotic coccinellid Harmonia axyridis (Pallas) and the native species Adalia bipunctata L. was investigated in the laboratory by determining the consumption of interspecific eggs by fourth instar larvae and adult females. Larvae and adult ladybirds were individually put into petri dishes at 25 °C with 20 eggs of the selected target species. The tests included three treatments: (a) only coccinellid eggs, (b) coccinellid eggs and 5 aphids, and (c) coccinellid eggs and 40 aphids. Intra-guild predation (IGP) by H. axyridis of eggs of the native species, A. bipunctata , was lower in comparison with egg cannibalism (CANN) by H. axyridis , for both adults and larvae. No differences were detected for larvae at the density of 5 aphids. IGP of exotic against the native species was never higher than CANN of native species. IGP of native species was never higher in comparison with CANN. A. bipunctata adult CANN was significantly higher than IGP at densities of 0 and 40 aphids. In the set of experiments on CANN and IGP an inverse correlation was observed between egg consumption by adults and larvae and aphid density. Our bioassays indicate that H. axyridis does not demonstrate IGP vs. native species at a higher level than CANN of native species. It appears that H. axyridis does show a high potential for CANN and therefore seems unlikely this species will to have a negative impact on native species by IGP of eggs.

On the Competition Occurring Between Aedes albopictus and Culex pipiens (Diptera: Culicidae) in Italy

Abstract Aedes albopictus (Skuse) was detected for the first time in Italy in 1990. Thanks to its high biological adaptability, it spread rapidly to colonize various urban areas in central and northern Italy. The purpose of this study was to examine the ecological niche occupied by Ae. albopictus and the role of competition with Culex pipiens L., which is a widespread indigenous species, in urban areas. The larval development cycle and competition for food between the two species was also studied under laboratory conditions. The study showed that both species can colonize any type of artificial water container. Ae. albopictus mainly occupies saucers under flower pots and other, usually smaller-sized, containers, whereas Cx. pipiens tends to develop more in large tanks (100–200 liters) used in residential gardens and other larger-sized containers. It would seem that the two species interact mainly in medium-sized containers (10–50 liters) such as manholes and tires. Laboratory studies showed that, at 25°C, the food-biomass conversion coefficient is significantly higher in Ae. albopictus than in Cx. pipiens, indicating that the new established species is more efficient in transforming food into biomass. As a consequence, it has a greater capacity to exploit food resources and therefore grow more rapidly than Cx. pipiens. In larval association where food was scarce, it was noted that competition between the two species takes place and is influenced by temperature: at 25 ± 2°C, Ae. albopictus prevails but is much less likely to do so at 20°C.

Attraction of male turnip moths Agrotis segetum (Lepidoptera: Noctuidae) to sex pheromone components and their mixtures at 11 sites in Europe, Asia, and Africa

Selected combinations of (Z)-5-decenyl, (Z)-7-dodecenyl, and (Z)-9-tetradecenyl acetates, the pheromone components of the turnip mothAgrotisSegetum were tested for field attractancy at six, two, and three sites in Europe, Asia, and Africa, respectively. At all of the sites in Eurasia and in northern Africa the ternary mixture of the acetates captured most males, while at the sites south of the Sahara in Africa, (Z)-5-decenyl acetate alone was responsible for attraction. Differences in male attraction among the populations studied confirm the existence of significant population variation in the pheromone ofA. segetum. Interpretation of the present results together with earlier studies suggests that this variation is more or less continuous in Eurasia and north Africa, while a clearly distinct pheromone type is present in the areas south of the Sahara desert.

Use of the Sterile Insect Technique Against Aedes albopictus in Italy: First Results of a Pilot Trial

In Europe, the mosquito Aedes albopictus (Skuse) is widespread in Italy, Albania and most probably in neighbouring Montenegro. Recent introductions have also been reported in France, Spain and southern Switzerland. In Italy, the species is currently recognized as the most noxious mosquito, thus requiring the implementation of intensive control programmes. Ae. albopictus is also a potential vector of human diseases, which has raised the issue of whether eradication campaigns are called for. This species is particularly suitable for application of the sterile insect technique (SIT) because of its urban-related distribution, recent introduction, low active dispersal potential, low population density which may be maintained by conventional control measures, and ease of mass-rearing. In 1999, a programme was initiated that focused on the application of the SIT against Ae. albopictus. A pilot rearing facility, targeted at the production of up to 20 000 male pupae per week has been established. Blood feeding is performed with a thermostatically controlled device using defibrinated bovine blood, egg hatching is stimulated with a nutrient broth culture, and egg counts conducted automatically. Larval density and larval diet are still being investigated in order to improve productivity, the separation of males is currently conducted at the pupal stage using calibrated metal sieves, and irradiation studies are performed at the 60Co plant Calliope, Italian National Agency for New Technologies, Energy and the Environment in Rome. During the summer of 2004, eight weekly sterile male pupal releases were organized in Rimini to evaluate sterile male performances in the field against a natural population. A significant difference was observed in the release area compared with the control area when the effects on egg fertility and egg density were cumulated. It is planned to continue the programme on a larger scale to improve rearing efficiency and obtain a preliminary benefit/cost evaluation.

Sex pheromone of European corn borer. - Ostrinia nubilalis: Polymorphism in various laboratory and field strains

Sex gland extracts ofOstrinia nubilalis females collected in the wild or laboratory-reared from Switzerland, Italy, and Hungary were analyzed. Individuals collected in the north of Switzerland contained (Z)- and (E)-11-tetradecenyl acetate at the approximate ratio of 97∶3 (Z type), in accordance with field responses of males and previous findings. On the other hand, females from a laboratory culture derived from field collections made in the same area and reared for four to five generations contained theZ andE isomers at ratios of ca. 3∶97 and 35∶65, respectively. In the south, one of the eight wild females analyzed was of theZ type and the rest intermediate, whereas males were predominantly trapped with blends of the two isomers containing 60 to 97E. In a laboratory culture reared for one to two generations from corn borers collected in Hungary, three of nine females were of the intermediate type and the restZ. Small amounts of (Z)-11-hexadecenyl acetate were detected in female glands of theE strain; however, no effect of this compound could be observed in the field.

γ Ray Dosimetry and Mating Capacity Studies in the Laboratory on Aedes albopictus Males

ABSTRACT In Italy, Aedes albopictus Skuse is currently recognized as the most dangerous mosquito, and as currently applied conventional control methods gave unsatisfactory results, we are developing alternative strategies such as the sterile insect technique. To find the optimal sterilizing dose, male pupae were exposed to different doses of &ggr; rays in the range 20–80 Gy, generated by a Cesium-137 source. The effects of male pupal age at irradiation and &ggr; ray dose on adult male emergence, sterility level, longevity, and mating capacity were evaluated, and dose-response curves of residual fertility were calculated. Radiation tests were also performed on female pupae to observe their reproductive capacity in case of accidental release. Results confirmed that the age at which the male pupa is irradiated is an important factor that affects the longevity of the adult, whereas the effect of age on the induced sterility level is less pronounced. When male pupae older than 30 h were irradiated, the longevity of the adults was not affected by doses up to 40 Gy. The 40-Gy dose appeared sufficient to induce high level of sterility (>99%) at any male pupal age for all the strains tested. The duration of coupling and the number of mated females per male appeared to be affected by the radiation received by male pupae only at doses higher than 40 Gy. The female pupae were more sensitive to radiation than male pupae, with strong reduction in fecundity and fertility at 20 Gy and complete suppression of oviposition at higher doses.

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

ABSTRACT 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 technicians 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 WBO 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 WBO males. The data obtained are discussed for their significance in planning sterile insect technique programs against Ae. albopictus.

Effect of temperature regime on diapause intensity in an adult-wintering Hymenopteran with obligate diapause

Osmia lignaria is a solitary bee that over-winters as a fully eclosed, cocooned, unfed adult. Our objective is to understand the effect of wintering temperature on diapause maintenance and termination in this species. We measure respiration rates and weight loss in individuals exposed to various wintering temperatures (0, 4, 7, 22 degrees C, outdoors) and durations (28, 84, 140, 196, 252 days). We use time to emerge and respiration response (respiration rate measured at 22 degrees C) as indicators of diapause intensity. Adults spontaneously lower their respiration rates to approximately 0.1 ml/gh within 1 month after adult eclosion, indicating obligatory diapause. Non-wintered individuals maintain low respiration rates, but lose weight rapidly and die by mid-winter. In wintered adults, two phases can be distinguished. First, respiration response undergoes a rapid increase and then reaches a plateau. This phase is similar in bees wintered at 0, 4 and 7 degrees C. In the second phase, respiration response undergoes an exponential increase, which is more pronounced at the warmer temperatures. Composite exponential functions provide a good fit to the observed respiration patterns. Adults whose respiration response has reached 0.45 ml/gh emerge promptly when exposed to 20 degrees C, indicating diapause completion. Individuals wintered for short periods do not reach such respiration levels. When exposed to 20 degrees C these individuals lower their metabolic rate, and their emergence time is extended. The relationship between respiration rates and emergence time follows a negative exponential function. We propose two alternative models of diapause termination to interpret these results.

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.

Tolerance Thresholds for Aedes albopictus and Aedes caspius in Italian Urban Areas

ABSTRACT 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.