Impact of a shared sugar food source on biological control of Tuta absoluta by the parasitoid Necremnus tutae

Abstract

Honeydew is a sugar-rich food source produced by sap-feeding insects, notably by major pests such as aphids and whiteflies. It is an important alternative food source for the adult stage of various key natural enemies (e.g., parasitoids), but it may be used also as food by agricultural pests. Necremnus tutae is an idiobiont parasitoid, and it is the most abundant larval parasitoid associated with the South American tomato pinworm, Tuta absoluta, in recently invaded European areas. The impact of N. tutae on T. absoluta populations was evaluated under greenhouse conditions with and without the presence of a honeydew producer, the aphid Macrosiphum euphorbiae. In addition, laboratory experiments were performed to evaluate the longevity of N. tutae and T. absoluta adults when fed with water, honey or honeydew produced by the aphid. In the greenhouse, N. tutae effectively reduced T. absoluta population by the end of the experiment, and this independently of the presence of the aphid; still the presence of M. euphorbiae led to delayed and reduced T. absoluta population peak when controlled by the parasitoid (there was a fourfold increase in parasitoid density in presence of aphid). The longevity of both N. tutae and T. absoluta females increased in the presence of honeydew (when compared to water only) under laboratory conditions; it hinted that honeydew could be used by an herbivore as T. absoluta. The interactions between the two phytophagous species showed contrasting effects, and this mostly independently of parasitoid presence. Tuta absoluta had no impact on aphid population dynamics. By contrast, the production of T. absoluta larvae was higher in the first part of the experiment as the adults lived longer (feeding on aphid honeydew) and produced more larvae. In the second part of the experiment, there were fewer T. absoluta larvae in the presence of the aphid, likely owing to resource competition and/or negative plant-mediated indirect interactions. We demonstrated that honeydew producers could impact parasitoid-host population dynamics both through direct and indirect interactions and that potential positive effects of a sugar food source toward a pest can be nullified in the long term by other negative effects occurring simultaneously.

Does the dose make the poison? Neurotoxic insecticides impair predator orientation and reproduction even at low concentrations

“…In summary, we observed that spinosad, chlorpyrifos and lambda‐cyhalothrin can be toxic to the predator N. tenuis, even at low concentrations, with effects on fertility and orientation. In addition to the laboratory results, field trials should be performed to confirm the toxicity of the compounds exploring different exposure routes (i.e., residual contact and ingestion of contaminated prey) and/or by testing the potential side effects toward insect parasitoids exploited in tomato crops 13,84,85 …”

“…[5][6][7][8][9] This is especially relevant in integrated pest management (IPM) programs in which natural enemies are often deliberately released and/or conserved to reduce pest populations. [10][11][12][13][14] Ecotoxicological screenings are usually based on guidelines developed by non-governmental institutions, and in the European Union (EU) the ecotoxicological risk assessment of pesticides towards non-target arthropods was developed in the Guidance Document on Terrestrial Ecotoxicology, 15 following the recommendation of the European standard characteristics of beneficials regulatory testing (ESCORT) of the Society of environmental toxicology and chemistry (SETAC) for non-bee arthropods. 16,17 Most ecotoxicology studies consist of laboratory trials aimed at testing the highest pesticide dose recommended by manufacturers.…”

“…For this reason, studies on the side effects of pesticides are encouraged to provide new insights to mitigate their negative impacts on non‐target beneficial arthropods 5–9 . This is especially relevant in integrated pest management (IPM) programs in which natural enemies are often deliberately released and/or conserved to reduce pest populations 10–14 …”

“… 5 , 6 , 7 , 8 , 9 This is especially relevant in integrated pest management (IPM) programs in which natural enemies are often deliberately released and/or conserved to reduce pest populations. 10 , 11 , 12 , 13 , 14 …”

Natural enemies associated with Tuta absoluta and functional biodiversity in vegetable crops

“…The biology of N. tutae (referred to as N. artynes) has been extensively studied (Calvo et al 2013;Chailleux et al 2014;Bodino et al 2016;Calvo et al 2016). Fitness of this parasitoids benefits from feeding on sugar-reach diet such as honey and honeydew (Arnó et al 2018b; de 4 Campos et al 2020). This species has been considered for inoculative release as a control strategy against T. absoluta by several companies that mass rear natural enemies.…”