The Effects of Natural Insecticides on the Green Peach Aphid Myzus persicae (Sulzer) and Its Natural Enemies Propylea quatuordecimpunctata (L.) and Aphidius colemani Viereck.

Botanical insecticides and soaps are frequently proposed as environmentally safer alternatives to synthetic insecticides. However, the efficacy and selectivity of these products are often only partially supported by empirical evidence. Here, we tested the effectiveness of five botanical insecticides, belonging to different categories, on the green peach aphid Myzus persicae (Sulzer) and their selectivity towards two natural enemies, the ladybird beetle Propylea quatuordecimpunctata (L.) and the parasitoid Aphidius colemani (Dalman). White thyme essential oil (EO), sweet orange EO, crude garlic extract and Marseille soap were tested and compared with a pyrethrin-based commercial product. Both direct spray assays and residual contact assays on treated cabbage leaf disks were carried out. The tested products had low efficacy against aphids when compared to pyrethrins but were in general less detrimental to ladybird beetle larvae, meaning that if applied against other pests, they have a lower chance of harming this agent of aphid biocontrol. Some of the products (soap, orange EO) did, however, show direct exposure toxicity toward ladybird larvae, and thyme EO had extensive phytotoxic effects on cabbage leaves, possibly indirectly leading to higher mortality in ladybird adults. These results underline the necessity for case-by-case evaluations of botanical insecticides.

Short- and long-term effects of commercial formulations of imidacloprid, spirotetramat, and mixtures of these active ingredients on pupae of Diaeretiella rapae (Hymenoptera: Braconidae) and its progeny.

BACKGROUND: Compatibility studies of insecticides and natural enemies usually focus on short-term lethal effects, without considering the long-term sublethal effects (including progeny). Even less-explored are the effects of commercial insecticides formulated with more than one active product. Short- and long-term lethal and sublethal effects were studied for the first time on the progeny of commercial formulations of spirotetramat, imidacloprid and a commercial mixture of these active ingredients on pupae of Diaeretiella rapae (M'ntosh) (Hymenoptera: Braconidae), an endoparasitoid of aphids considered to be a potential biological control agent. Insecticides were exposed topically on aphid mummies in which the parasitoid was in the pupal stage. RESULTS: Imidacloprid reduced adult emergence by more than 30% and prolonged intra-host development time with respect to control from half the maximum recommended field dose (MFRD). Spirotetramat and commercial mixture only showed significant effects on these endpoints at doses above the MFRD. The tested formulations did not affect adult longevity, sex ratio, and percentage of parasitism in the exposed generation. At low concentrations the active ingredients in the commercial mixture behave synergistically, whereas at medium and high concentrations they behave antagonistically. Considering the 10% lethal dose (LD10), imidacloprid showed the highest hazard coefficient, whereas the commercial mixture was more hazardous when considering the LD50 and LD90. The commercial mixture and imidacloprid induced higher adult emergence and altered the sex ratio in the progeny. CONCLUSIONS: The following order of toxicity on D. rapae can be established: imidacloprid > commercial mixture > spirotetramat. Joint use of this species with imidacloprid and commercial mixture should be avoided in integrated pest management programs. © 2024 Society of Chemical Industry.

Assessment of Boll Weevil Susceptibility to Isocycloseram and Ethiprole and Differential Toxicity to Natural Enemies.

Insecticides efficient against the target species while conserving natural enemies in the agroecosystem are required for IPM. With the imminent discontinuation of fipronil, a broad-spectrum insecticide, ethiprole, which belongs to the same group as phenylpyrazole (2B), and isocycloseram, a novel isoxazoline insecticide with distinct mode of action (30), provide options for controlling boll weevil. The susceptibility of the boll weevil, Anthonomus grandis grandis (Boh.), and two natural enemies [Eriopis connexa (Germar) and Bracon vulgaris Ashmead] to these insecticides were studied. Furthermore, the survival and biological traits of the lady beetle, E. connexa, exposed to fipronil, isocycloseram, and ethiprole were assessed. The LC50s values for fipronil, ethiprole, and isocycloseram for A. grandis grandis were 2.71, 0.32, and 0.025 mg a.i./L, respectively; 0.86, > 200, and 3.21 mg a.i./L for E. connexa; and 2.31, 592.94, and 0.18 mg a.i./L for B. vulgaris, respectively. The recommended rates of ethiprole did not cause mortality in adult lady beetles, although fipronil and isocycloseram were highly toxic. Lady beetle larvae and adults survived more than 80% when exposed to dried residues of ethiprole, but less than 10% when exposed to fipronil and isocycloseram. Lady beetle larvae development, reproduction, and predation rates of adults were similar between ethiprole and the control group. Although fipronil and ethiprole belong to the same insecticide group, the difference in toxicity to boll weevils and natural enemies is presented and discussed. Ethiprole was more toxic to boll weevils than to its parasitoid and lady beetle, and isocycloseram was highly toxic to all three species.