Lethal and Sub-lethal Effects of Four Insecticides on the Aphidophagous Coccinellid Adalia bipunctata (Coleoptera: Coccinellidae)

Lethal and Sub-Lethal Effects of Organic-Production-Approved Insecticides and Fungicides on the Predator Macrolophus pygmaeus (Rambur) (Hemiptera: Miridae)

In this study, the effects of paraffin oil, copper hydroxide, copper oxychloride, wettable sulfur, Beauveria bassiana and deltamethrin, as a toxic reference treatment, on the survival and predation rate of M. pygmaeus were investigated. In each treatment, the prey were classified as slightly, partially or fully consumed. The mortality rate after contact exposure was high (66.6%) when nymphs were treated with copper hydroxide but much lower after residual exposure (6.6%). B. bassiana caused 53.3% and 46.6% mortality via contact and residual exposure, respectively. The total prey consumption was significantly lower in the pyrethroid reference treatment control and B. bassiana treatments. The highest percentage of slightly consumed prey was recorded in the toxic reference and B. bassiana treatments, that of partially consumed prey in the copper hydroxide treatment and, finally, that of fully consumed prey in the paraffin oil treatment. Therefore, assessing the sub-lethal effects by separating the prey killed into slightly, partially and fully consumed is a sensitive approach to detect impacts which otherwise may remain unnoticed. The results provide information for the most appropriate use of M. pygmaeus in IPM programs and introduce more sensitive approaches in the detection of side-effects of pesticides on M. pygmaeus and other hemipteran predators.

Effects of three chitin synthesis inhibitors on egg masses, nymphs and adults of Halyomorpha halys (Hemiptera: Pentatomidae)

BACKGROUND

Halyomorpha halys, (brown marmorated stink bug, BMSB), is a high-concern invasive species causing severe damage to orchards in many countries outside its native Asian range. Management methods other than frequent sprays of broad-spectrum insecticides are needed to restore integrated pest management (IPM) practices in orchards. Chitin synthesis inhibitors are usually regarded as desirable options in IPM programs because of lower toxicity to beneficial insects and non-target organisms compared to neurotoxic insecticides. In this study, the activity of three chitin synthesis inhibitors (namely buprofezin, novaluron and triflumuron) was investigated on BMSB egg masses, third instars and adults by means of laboratory bioassays.

RESULTS

Novaluron and to a lesser extent triflumuron were detrimental to BMSB nymphs exposed to residues on potted peach plants. Novaluron caused high mortality among early instars that emerged from sprayed egg masses. No significant differences were found between buprofezin and water control on eggs or third instars. When sprayed on BMSB adults, none of the chitin synthesis inhibitors affected survival, fecundity, or egg hatching.

CONCLUSION

Given the activity on nymphs, but the lack of effects on adults, novaluron and triflumuron might be considered for field applications only as a tool in a wider management strategy along with other methods aimed at preventing the invasion of crops by BMSB adults. © 2023 Society of Chemical Industry.

Impact of Triflumuron on Halyomorpha halys (Hemiptera: Pentatomidae): Laboratory and Field Studies

Halyomorpha halys, (the brown marmorated stink bug, BMSB), is a high-concern invasive species causing severe damage to orchards in many countries outside its native Asian range. Control options matching both effectiveness and sustainability are currently lacking. Inhibitors of chitin biosynthesis might be exploited for integrated management programs because of the overall better ecotoxicological profile in comparison with most neurotoxic insecticides used so far against BMSB. In this study, the activity of triflumuron, a benzoylphenyl urea hampering chitin biosynthesis, was tested on BMSB in laboratory and field conditions. In laboratory bioassays, the insecticide was sprayed on potted peach plants (30 cm high) and residues were aged in a glasshouse for 0, 7, 14, and 21 d. Then, third-instar bugs were placed on the plants and continuously exposed to residues. Mortality was scored after 7, 14, and 21 d exposure. Triflumuron caused significantly higher mortality on BMSB nymphs in comparison with water controls at all aging periods. Moreover, aging of residues up to 21 d did not cause any significant reduction of activity. Field experiments were also carried out in 2019 in eight pear orchards. Injuries to fruits at harvest were compared between plots where triflumuron was added to insecticide sprays against BMSB and control plots managed exactly in the same way but without any triflumuron treatment. An overall mean of 9.99 ± 1.98% stink bug injured fruits was detected in plots managed with the strategy including triflumuron, whereas 19.45 ± 3.55% of fruits were injured in plots assigned to controls.

Scope for non-crop plants to promote conservation biological control of crop pests and serve as sources of botanical insecticides

Besides providing food and shelter to natural enemies of crop pests, plants used in conservation biological control interventions potentially provide additional ecosystem services including providing botanical insecticides. Here we concurrently tested the strength of these two services from six non-crop plants in managing cabbage pests in Ghana over three successive field seasons. Crop margin plantings of Ageratum conyzoides, Tridax procumbens, Crotalaria juncea, Cymbopogon citratus, Lantana camara and Talinum triangulare were compared with a bare earth control in a three-way split plot design such that the crop in each plot was sprayed with either a 10% (w/v) aqueous extract from the border plant species, a negative control (water) and a positive control (emamectin benzoate 'Attack' insecticide). Pests were significantly less numerous in all unsprayed treatments with non-crop plant margins and in corresponding sprayed treatments (with botanical or synthetic insecticide positive control) while treatments with bare earth margin or sprayed with water (negative controls) had the highest pest densities. Numbers of predators were significantly depressed by synthetic insecticide but higher in other treatments whether unsprayed or sprayed with botanical insecticide. We conclude that some plant species have utility in both conservation biological control and as source of botanical insecticides that are relatively benign to natural enemies. In this crop system, however, the additional cost associated with using botanical insecticides was not justified by greater levels of pest suppression than achieved from border plants alone.

Sublethal Effects of Four Insecticides on the Seven-Spotted Lady Beetle (Coleoptera: Coccinellidae)

To further develop integrated pest management (IPM) strategies against two sucking insect pests, Aleurocanthus spiniferus (Quaintanca) (Hemiptera: Aleyrodidae) and Toxoptera aurantii Boyer (Hemiptera: Aphididae), in Chinese tea plantations, it is important to evaluate the effects of insecticides on biological control agents, such as the seven-spot lady beetle, Coccinella septempunctata L. (Coleoptera: Coccinellidae). Therefore, we tested the toxicity and sublethal effects of spirotetramat, clothianidin, lambda-cyhalothrin, and bifenthrin on C. septempunctata. The side effects of the active ingredients of the insecticides were evaluated with residual contact tests on the larvae of C. septempunctata in the laboratory. Spirotetramat and clothianidin exhibited lower lethality to C. septempunctata as shown by the higher LC50 values and had higher selectivity for A. spiniferus and T. aurantii based on the selective toxicity ratios being superior to other tested insecticides. Spirotetramat also did not affect survival, longevity, fecundity, and egg hatching of C. septempunctata. Clothianidin and bifenthrin prolonged the duration of larval development stages of C. septempunctata obviously. Clothianidin at >2.5 mg/liter, lambda-cyhalothrin at >0.03 mg/liter, and bifenthrin at >0.125 mg/liter significantly reduced the survival and pupation rates of C. septempunctata larvae. Furthermore, spirotetramat at 3.125 mg/liter was harmless (IOBC class 1) to larvae of this coccinellid species. Based on the results, spirotetramat was innocuous to C. septempunctata larvae compared with clothianidin, lambda-cyhalothrin, and bifenthrin. Therefore, spirotetramat might be incorporated into IPM programs in combination with C. septempunctata for control of A. spiniferus and T. aurantii in the tea plantations.

Spinosyns Cause Aedeagus Eversion in Carpophilus spp. (Coleoptera: Nitidulidae)

During an assessment of various insecticides against sap beetles, Carpophilus sp., it was noted that at least some males everted their reproductive structures (referred to as aedeagus from here forward) when treated with a spinosyn insecticide, spinetoram. This response to spinosyns or other insecticides is not documented in the literature even though sap beetles have been included in numerous insecticide assays and spinosyn insecticides have been in widespread commercial use for >20 yr. Additionally, other insect species have not been documented to show a similar aedeagus eversion response to spinosyns or other insecticides. The objective of this study was to further examine eversion of the aedeagus when sap beetles were exposed to different rates of two spinosyn insecticides, spinetoram and spinosad. Additionally, we examined whether a similar response would occur in other insects when three species of Coccinellidae (Coleoptera) and one species of Curculionidae (Coleoptera) were exposed to spinetoram. Our results show that male sap beetles respond to both spinosyns by everting the aedeagus, females did not have an analogous response. No similar response was observed for the assayed species of Coccinellidae or Curculionidae.

Response of the European Ladybird Adalia bipunctata and the Invasive Harmonia axyridis to a Neonicotinoid and a Reduced-Risk Insecticide

The spread of the multicolored Asian lady beetle Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) in Europe coincided with the decline of the native Adalia bipunctata (L.) (Coleoptera: Coccinellidae). Both species are predators of aphids in orchards, and differential susceptibility to insecticides used to control fruit pests may contribute to explain the competitive advantage of the invasive over the native species. In this study, the insecticidal activity of imidacloprid and spinetoram was tested on third instars and adults of both ladybird species under laboratory conditions. Insects were exposed to insecticide residues on potted peach plants that were sprayed with the maximum recommended field doses (100 mg/liter for imidacloprid and 66.67 mg/liter for spinetoram). Mortality was scored after short (2 d for both stages) and long (7 and 10 d for adults and larvae, respectively) exposure periods. The susceptibility to the insecticides was very similar for H. axyridis and A. bipunctata. Imidacloprid caused a significant increase in the mortality of both stages of the two species for every exposure period. On the other hand, when exposed to spinetoram residues, larvae and adults of both ladybirds did not show higher mortality than controls after short and long exposure periods. The pest suppression provided by ladybirds, which could be severely hampered by the applications of nonselective pesticides, might be enhanced by the adoption of reduced-risk insecticides, selective for these beneficial insects.

Characterization of Vitellogenin and Vitellogenin Receptor of Conopomorpha sinensis Bradley and Their Responses to Sublethal Concentrations of Insecticide

Conopomorpha sinensis Bradley is the dominant borer pest of Litchi chinesis and Euphoria longan. Current management of C. sinensis relies upon insecticide application to adult moths. In addition to the direct mortality induced by insecticides, a sublethal dose of insecticides also affects growth, survival, and reproduction in the exposed insects. Vitellogenin (Vg) and vitellogenin receptor (VgR) are normally identified as essential reproduction-related proteins in insects. In this study, we characterized these two genes from C. sinensis, and investigated their differential responses to sublethal concentrations of insecticide. Cloned CsVg and CsVgR consist of 5391 and 5424-bp open reading frames, which encode proteins of 1796 and 1807 amino acid residues, respectively. The CsVg protein contains the typical vitellogenin, DUF1943 and VWFD domains as other reported lepidopteran Vgs. The CsVgR was characterized as a typical low density lipoprotein receptor with two highly conserved LBD and EGF precursor domains, one hydrophobic transmembrane domain, one cytoplasmic domain, and 13 putative N-glycosylation sites. We next assessed the sublethal effect of four major insecticides on egg-laying in C. sinensis. The toxicity against C. sinensis varied among the insecticides tested, with LC₅₀ values ranging from 0.23 ppm for chlorpyrifos to 20.00 ppm for β-cypermethrin, among which emamectin benzoate (EB) showed a significant negative impact on egg-laying, survival rate, ovarian development, and mating rate of C. sinensis at LC₃₀ doses. Further investigation showed that the transcriptional level of CsVg and CsVgR were impaired in different way at 24, 48, and 72 h after EB exposure, and this result was in agreement with the diminished egg-laying of C. sinensis in the sublethal concentration EB-treated group. A repressed transcription level of CsVgR was observed at 48 h after treatment, suggesting that EB elicits a delayed response in the abundance of CsVgR. These results established different roles of CsVg and CsVgR in response to the sublethal effect of insecticides. CsVg might be a better parameter than CsVgR for assessing the effect of sublethal insecticides on reproduction in C. sinensis.