Lucia Zappalà

The non-target impact of spinosyns on beneficial arthropods

Spinosyn-based products, mostly spinosad, have been widely recommended by extension specialists and agribusiness companies; consequently, they have been used to control various pests in many different cropping systems. Following the worldwide adoption of spinosad-based products for integrated and organic farming, an increasing number of ecotoxicological studies have been published in the past 10 years. These studies are primarily related to the risk assessment of spinosad towards beneficial arthropods. This review takes into account recent data with the aim of (i) highlighting potentially adverse effects of spinosyns on beneficial arthropods (and hence on ecosystem services that they provide in agroecosystems), (ii) clarifying the range of methods used to address spinosyn side effects on biocontrol agents and pollinators in order to provide new insights for the development of more accurate bioassays, (iii) identifying pitfalls when analysing laboratory results to assess field risks and (iv) gaining increasing knowledge on side effects when using spinosad for integrated pest management (IPM) programmes and organic farming. For the first time, a thorough review of possible risks of spinosad and novel spinosyns (such as spinetoram) to beneficial arthropods (notably natural enemies and pollinators) is provided. The acute lethal effect and multiple sublethal effects have been identified in almost all arthropod groups studied. This review will help to optimise the future use of spinosad and new spinosyns in IPM programmes and for organic farming, notably by preventing the possible side effects of spinosyns on beneficial arthropods.

Do Biopesticides Affect the Demographic Traits of a Parasitoid Wasp and Its Biocontrol Services through Sublethal Effects

Pesticide risk assessments are usually based on short-term acute toxicity tests, while longer-term population dynamic related traits, critical to the success of biological control and Integrated Pest Management (IPM) programs, are often overlooked. This is increasingly important with respect to new biopesticides that frequently cause no short-term acute effects, but that can induce multiple physiological and behavioral sublethal effects, leading to a decrease in population growth and ecosystem services. In this study we assessed the lethal and sublethal effects of six biopesticides [abamectin, azadirachtin, Bacillus thuringiensis, borax plus citrus oil (Prev-Am®), emamectin benzoate, and spinosad], used in tomato crops to control the invasive pest Tuta absoluta (Lepidoptera: Gelechiidae), on adults and pupae of the parasitoid Bracon nigricans (Hymenoptera: Braconidae). Data on female survival and production of female offspring were used to calculate population growth indexes as a measure of population recovery after pesticide exposure. Spinosad caused 100% and 80% mortality in exposed adults (even 10 d after the treatment) and pupae, respectively. Although most of the biopesticides had low levels of acute toxicity, multiple sublethal effects were observed. The biocontrol activity of both females that survived 1-h and 10-d old residues, and females that emerged from topically treated pupae was significantly affected by the application of the neurotoxic insecticides emamectin benzoate and abamectin. Furthermore, very low B. nigricans demographic growth indices were estimated for these two insecticides, indicating potential local extinction of the wasp populations. Among the tested products, Bt proved to be the safest for B. nigricans adults and pupae. Our findings emphasize that acute toxicity assessment alone cannot fully predict the actual impact of pesticides on non-target parasitoids. Thus, sublethal effects related to the species specific life-history variables must be carefully considered in order to assess pesticide risks and to incorporate new pesticides, including biopesticides, into IPM programmes.

Efficacy of sulphur on Tuta absoluta and its side effects on the predator Nesidiocoris tenuis

The South American tomato pinworm, Tuta absoluta (Meyrick), is one of the major pests of tomato crop. Since its detection in the Mediterranean basin, it has been commonly controlled using chemical insecticides. However, inoculation and conservation of predatory mirids, integrated with sprays of selective insecticides, has been demonstrated to be a cost‐effective strategy for controlling this pest. In this work, we tested the efficacy of two sulphur formulations, dustable and wettable powder, for controlling T. absoluta on tomato under greenhouse and open‐field conditions. In addition, the side effects of both sulphur formulations on the predator, Nesidiocoris tenuis (Reuter), were evaluated under laboratory conditions. Dustable sulphur, applied weekly on tomato seedlings artificially infested with T. absoluta in greenhouse conditions, significantly reduced the infestation levels and was demonstrated to have a repellent effect on oviposition. Wettable sulphur was not effective for controlling T. absoluta populations in both greenhouse and open‐field experiments. In the side effect trials conducted with N. tenuis, only dustable sulphur resulted in being moderately harmful as a fresh residue and slightly harmful as a 7‐day‐old residue; no effects were recorded exposing the predator to 14‐day‐old sulphur residues. In contrast, wettable sulphur was classified as harmless to N. tenuis. Our results suggest that the use of sulphur, especially as dustable powder, could be considered as a tool in T. absoluta management strategies, although its side effects on N. tenuis should be taken into account. The implications of these results for the use of sulphur formulations in pest and disease management programmes in tomato crops are discussed.

Biology and developmental strategies of the Palaearctic parasitoid Bracon nigricans (Hymenoptera: Braconidae) on the neotropical moth Tuta absoluta (Lepidoptera: Gelechiidae).

ABSTRACT During the years after the invasion of Western Palaearctic tomato crops by the South American tomato leafminer, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), several indigenous generalist parasitoids have been recorded on this new host. Among these, Bracon nigricans Szépligeti (Hymenoptera: Braconidae) is widely distributed in the Palaearctic region, and has been frequently recovered from South American tomato leafminer. However, most of the available data on this species deal with taxonomic aspects and its recovery in faunistic surveys. The current study documents the biology of B. nigricans on South American tomato leafminer, and provides a scientific basis for its inclusion in South American tomato leafminer management programs in Afro-Eurasia. We studied several B. nigricans life-history traits relevant to juvenile development and reproduction by females. B. nigricans proved to be an idiobiont and a synovigenic ectoparasitoid of mature South American tomato leafminer larvae. Several B. nigricans reproductive traits were influenced by the age of the mothers; on average, the progeny had a slightly male-biased sex ratio (60% males) and a low rate of successful development (≈37%). Adult females lived 42.8 d and produced an average of 29.8 offspring. These biological parameters yielded an intrinsic rate of increase of 0.052. Females showed behavioral plasticity in host use, as initial host paralysis was followed by host-feeding, oviposition, or host rejection, with a consequent high mortality rate among hosts exposed to parasitism. Although further field studies are needed, these data, obtained in laboratory conditions, suggest that B. nigricans should be considered as a potential biological control agent of in newly invaded areas of the Palaearctic region.

Life stage-dependent susceptibility of Aphytis melinus DeBach (Hymenoptera: Aphelinidae) to two pesticides commonly used in citrus orchards

The assessment of pesticides compatibility with natural enemies is recommended before including agrochemicals in integrated and organic pest management schemes. The lethal and sublethal effects of a mineral oil and a juvenile hormone mimic (pyriproxyfen), on adults and larvae of Aphytis melinus, a key ectoparasitoid of armored scale insect pests of citrus, such as Aonidiella aurantii, were evaluated. Mineral oil caused very high mortality on the adults, while a lower acute toxicity was recorded on young instars. No significant effects on their reproduction capacity and on the sex-ratio of the progeny were observed. Pyriproxyfen had neither lethal nor sublethal effects (in terms of survived female fertility) on A. melinus adults. However, parasitoid larvae exposed to this insecticide suffered strong acute toxicity and fertility reduction (progeny number and proportion of female progeny). When adults were offered the choice to parasitize treated and untreated scales they significantly preferred the control ones, and when they were exposed to only treated scaled the parasitism rate was significantly lower only with mineral oil-treated hosts. The significant differences in the susceptibility of the two parasitoid instars highlight the importance of including this aspect in pesticide risk assessment procedures and in the choice of the pesticide and of the treatment timing in the field. Overall, the results indicate potential for integrating A. melinus, both naturally present and artificially released, and these insecticides only by appropriate timing of insecticide spraying and parasitoid releases.

Can alternative host plant and prey affect phytophagy and biological control by the zoophytophagous mirid Nesidiocoris tenuis

Nesidiocoristenuis (Reuter) (Hemiptera: Miridae) is an important natural enemy of several key arthropod pests. However, in tomato crop this predator can cause economic damage owing to its zoophytophagous behavior. We investigated in laboratory conditions the influence of two alternative plants, Dittrichiaviscosa L. (Asteraceae) and Sesamumindicum (L.) (Pedaliaceae), with or without prey, on N. tenuis damage and its biological control services on Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) eggs. Both D. viscosa and S. indicum, as companion plants in dual-choice bioassays, significantly reduced the damage of the mirid on tomato. S. indicum was more attractive than D. viscosa for feeding and oviposition and its presence did not interfere with the predation on T. absoluta eggs. We also studied the potential of the three plants as preyless rearing substrate for the mirid, and only S. indicum showed to be a suitable host plant for N. tenuis development and oviposition. The potential applications of S. indicum in N. tenuis field management and mass rearing are discussed.

Citrus Pest Management in the Northern Mediterranean Basin (Spain, Italy and Greece)

Main management options for Arthropod pests of citrus and species recently introduced in the northern Mediterranean regions are reviewed. Available control strategies are discussed, incuding visual inspections practices, insect trapping methods and parasitoids or parasites release in augmentative or classical biological control. IPM practices and side effects of pesticides are also reviewed.

Combined Non-Target Effects of Insecticide and High Temperature on the Parasitoid Bracon nigricans.

We studied the acute toxicity and the sublethal effects, on reproduction and host-killing activity, of four widely used insecticides on the generalist parasitoid Bracon nigricans (Hymenoptera: Braconidae), a natural enemy of the invasive tomato pest, Tuta absoluta (Lepidoptera: Gelechiidae). Laboratory bioassays were conducted applying maximum insecticide label rates at three constant temperatures, 25, 35 and 40°C, considered as regular, high and very high, respectively. Data on female survival and offspring production were used to calculate population growth indexes as a measure of population recovery after pesticide exposure. Spinetoram caused 80% mortality at 25°C and 100% at higher temperatures, while spinosad caused 100% mortality under all temperature regimes. Cyantraniliprole was slightly toxic to B. nigricans adults in terms of acute toxicity at the three temperatures, while it did not cause any sublethal effects in egg-laying and host-killing activities. The interaction between the two tested factors (insecticide and temperature) significantly influenced the number of eggs laid by the parasitoid, which was the lowest in the case of females exposed to chlorantraniliprole at 35°C. Furthermore, significantly lower B. nigricans demographic growth indexes were estimated for all the insecticides under all temperature conditions, with the exception of chlorantraniliprole at 25°C. Our findings highlight an interaction between high temperatures and insecticide exposure, which suggests a need for including natural stressors, such as temperature, in pesticide risk assessments procedures.

Fortuitous parasitoids of the invasive tomato leafminer Tuta absoluta in Tunisia

The South American tomato leafminer, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), is a major threat to tomato (Solanum lycopersicum L.) crops. After its first detection in Spain in 2006, it spread rapidly through the Western Palaearctic region, arriving in Tunisia 2 years later. The aim of this research was to assess whether generalist indigenous parasitoids are adapting to this exotic host in Tunisian tomato crops. For this, we conducted a survey in four Tunisian tomato-growing areas by sampling infested leaves of tomato and solanaceous weeds and exposing artificially infested sentinel plants. Two ectoparasitoid species were found attacking and developing on T. absoluta: Bracon sp. (Hymenoptera: Braconidae) and Necremnus sp. nr artynes (Hymenoptera: Eulophidae), whereas no egg or pupal parasitoids were found. The eulophid wasp was the most abundant with a peak of apparent parasitism rate of 25.5%. It emerged from parasitized T. absoluta young larvae in exposed sentinel plants and in sampled infested tomato leaves, both in greenhouse and open field cultivations. Bracon sp. showed a gregarious development on T. absoluta mature larvae and it was collected only on sentinel plants exposed in the Ragueda (Kiarouan) site, with 10.23% of estimated parasitism. Although further research is still needed to assess properly the ecological role of these parasitoids in the biological control of T. absoluta, this study represents the first step toward establishing the scientific basis for including these parasitoids in the Tunisian IPM and biological programs against this pest.

Potential Toxicity of α-Cypermethrin-Treated Nets on Tuta absoluta (Lepidoptera: Gelechiidae)

ABSTRACT Insect-proof nets are thought to be effective physical barriers to protect tomato crops against several insect pests, including the invasive tomato pest, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae). However, protected tomato crops are frequently infested by this destructive pest, and there is a higher infestation of plants closer to openings in Mediterranean greenhouses, suggesting that immigrating adults can easily walk on these protective materials and find a way to reach the crop. Laboratory bioassays were carried out to characterize the potential toxicity of &agr;-cypermethrin-treated insect-proof nets (Agronet) against T. absoluta adults. The data showed that the net acts mainly through a variety of chronic sublethal effects rather than acute ones. Reduced longevity and, more markedly, a reduced number of laid eggs were observed after the moths were exposed to the treated net over the duration of their lifetimes. A Y-tube experiment showed that the treated net does not affect the T. absoluta olfaction cues for host location. In contrast, when the moths were given the option to choose either the treated or the untreated net in laboratory cages, they significantly preferred the untreated one. The toxicological significance and the functional implications of these subtle effects for the implementation of integrated T. absoluta management strategies are discussed.