Evaluation of the Effect of Fungatol and Gamma-T-ol on the Emergence and Adult Parasitoid Survival of Mummies of Cotton Aphids Parasitized by Aphidius colemani

Beneficial insects play a major role in controlling pest populations. In sustainable agricultural production systems, control methods compatible with integrated pest management (IPM) are preferred over broad-spectrum pesticides. EOs from aromatic plants may provide a new and safe alternative to synthetic chemicals. In this research, the efficacy of Fungatol, Gamma-T-ol, Fungatol plus neem, and Gamma-T-ol plus neem was evaluated against Aphidius colemani Viereck (Hymenoptera: Braconidae; Aphidiidae), the parasitoid of the cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae). Under laboratory and greenhouse conditions, five different concentrations of each formulation were applied to parasitized mummies and adult parasitoids. Results for parasitoid emergence from aphid mummies sprayed with different concentrations of Fungatol, Gamma-T-ol, Fungatol plus neem, and Gamma-T-ol plus neem in the laboratory and glasshouse showed that the formulations did not adversely affect adult emergence as rates above 60% were observed. For residual toxicity tests done by exposing adult parasitoids to a fresh, dry biopesticide film sprayed on glass plates, less than 20% mortality was observed after 48 h of exposure. Adult longevity tests revealed that the highest concentrations of some of the formulations evaluated were slightly toxic to A. colemani. According to the IOBC rating, our results indicated that most of the tested concentrations for each formulation were harmless to A. colemani. Based on the above results, it may be proposed that the formulations evaluated in this study are potential botanical pesticide candidates for incorporation into an IPM program.

Aphicidal activities of Moroccan Bacillus thuringiensis strains against cotton aphid (Aphis gossypii)

The objective of this study was to evaluate the insecticidal effect of toxins from Moroccan Bacillus thuringiensis strains (Berliner) (Bt) on Aphis gossypii (Homoptera: Aphididae). Aphis gossypii is one of the most pests of Moroccan crops. Their management is based traditionally on using chemical products. Some of them are well known to be potentially toxic to the environment and human health. Therefore, alternative strategies for aphid management in crops have been developed in recent years, including a biological control using toxins of bacterial strains. In this study, the artificial diet bioassay was used to screen the aphicidal effect of 82 Bt toxins against first instar nymphs and third instar nymphs of A. gossypii. Among the examined Bt strains, eleven showed a high insecticide activity against A. gossypii stages. In addition, the assessment of the lethal concentration (LC50) of selected Bt revealed that the local BtA4, BtA1 and Bt21.6 exhibited higher insecticidal activity against first instar nymphs of A. gossypii (LC50 (BtA4)=0.15, LC50 (BtA1)=0.23 and LC50 (Bt21.6)=0.25 mg/ml) and the selected strains BtB6, BtA10 and Bt21.6 exhibited the relatively best activity third instar nymphs of A. gossypii (LC50 (BtB6)= 0.48, LC50 (BtA10)= 0.79 and LC50 (Bt21.6)= 1.14 mg/ml) of A. gossypii. Therefore, the results of this study indicate that the selected B. thuringiensis strains have great potential to be used in the integrated A. gossypii management.

Transgenerational Effects of a Neonicotinoid and a Novel Sulfoximine Insecticide on the Harlequin Ladybird

The harlequin ladybird, Harmonia axyridis Pallas (Coleoptera: Coccinellidae), is a generalist predator and an effective biocontrol agent of various insect pests that has been exploited for the control of aphid pests in the greenhouse and field. However, insecticides are widely used to control aphid pests worldwide and the potential non-target effects of sulfoxaflor and imidacloprid for controlling aphid pests towards this biocontrol agent are little known. Although both sulfoxaflor and imidacloprid act on nicotinic acetylcholine receptors of insects, sulfoxaflor has a novel chemical structure compared with neonicotinoids. We assessed the lethal, sublethal and transgenerational effects of sulfoxaflor and imidacloprid on H. axyridis simultaneously exposed via ingestion of contaminated prey and via residual contact on the host plant at LC20 and LC50 doses estimated for the cotton aphid. Imidacloprid significantly reduced the survival of H. axyridis adults compared to sulfoxaflor at the same lethal concentration against cotton aphid. Both concentrations of imidacloprid and sulfoxaflor reduced the proportion of ovipositing females, and both concentrations of imidacloprid and sulfoxaflor, except LC20 dose of sulfoxaflor, reduced the fecundity and fertility of the parental generation. In the progeny of imidacloprid- and sulfoxaflor-exposed parents, both tested LC50 concentrations significantly decreased the juvenile survival rate, and both concentrations of imidacloprid and sulfoxaflor, except LC20 dose of sulfoxaflor, prolonged the development time. Our findings provide evidence of the negative influence of imidacloprid and sulfoxaflor at low lethal concentrations on the harlequin ladybird and on the progeny of exposed individuals, i.e., transgenerational effects. Hence, these findings stress the importance of optimizing the applications of imidacloprid and sulfoxaflor for the control of aphid pests, aiming at preserving the biocontrol services provided by H. axyridis throughout the integrated pest management approach.

Cotton aphid feeding preference and the development of watermelon plants treated with silicon

The cotton aphid is one of the main watermelon crop pests and may cause a reduction in productivity due to the suction of sap, the transmission of viruses, and decreased photosynthetic capacity. The objective of this research was to evaluate the feeding preference of the aphid Aphis gossypii and the biometric aspects of watermelon cultivar plants submitted to silicon application. The experiment was conducted at the Institute of Education, Agriculture, and Environment of the Federal University of Amazonas, in Humaitá, Brazil. A randomized complete block design was used for testing preference with choice and a completely randomized design to study the biometric parameters of the plants. The treatments were distributed in a 2 x 3 factorial scheme (with and without silicon and considering cultivars Crimson Sweet, Fairfax, and Charleston). Silicic acid was applied at a 1% concentration directly on the substrate around the plants (equivalent to 1 t SiO2 ha-1), 25 days after sowing. The aphids in the breeding were kept in cucumber plants of cultivar Caipira. The treatments were evaluated through the preference test on watermelon cultivars and biometric studies of plant growth and development. The data were submitted to an analysis of variance, and the means were compared using the F and Scott-Knott tests at the 5% probability level. Silicon does not affect the preference of Aphis gossypii in different watermelon cultivars and negatively affects plant growth and development.

Botanical formulations for the ecological management of Myzus persicae (Sulzer) and Aphis gossypii (Clover) (Hemiptera: Aphididae) and their side effects on parasitoids

The peach aphid Myzus persicae (Sulzer) and cotton aphid Aphis gossypii (Clover) (Hemiptera: Aphididae) are considered to be key pests affecting greenhouse pepper crops in Argentina as a result of their frequent occurrence and the seriousness of the damage caused by their feeding behavior and the transmission of virus. The goal of this research was to determine the efficiency of botanical products to control aphids and their side effects on parasitoids in this crop. Thus, three biorational pest control formulations derived from essential oils (EO) and plant extracts (Es) were tested, namely (i) neem EO, cinnamon EO, clove EO, oregano EO and American marigold EO (formulation 1); (ii) garlic EO and cinnamon EO (formulation 2); (iii) garlic E and rue E (formulation 3); and a soy lecithin adjuvant (lecithin), and finally, a control (water spray method). For this research, a completely randomized design was replicated 3 times. These treatments were applied directly to the foliage by means of a backpack sprayer on a weekly basis until the end of this trial. Subsequently, the total number of healthy aphids and parasitized aphids (mummies) on every leaf was recorded in the field and the laboratory through repeated measures Analysis of Variance (ANOVA) and LSD Fisher method. The results showed that formulation 1 and formulation 3 recorded a lower number of aphids and mummies compared to the other treatments. This evidence would demonstrate that these formulations repel aphids and parasitoids without the lethal effects caused by the use of broad spectrum insecticides.

Evidence for the Involvement of the Chemosensory Protein AgosCSP5 in Resistance to Insecticides in the Cotton Aphid, Aphis gossypii

It has been speculated that insect chemosensory proteins (CSPs) may have additional roles beyond olfaction. In this study, the phylogenetic and genomic analyses of the CSPs of the cotton aphid, Aphis gossypii, revealed the presence of gene gain-and-loss among different aphid field populations. Differential expressions of eight CSP genes were demonstrated after treatments with insecticides of different modes of action. The expression of AgosCSP5 was significantly upregulated by the insecticide treatments in a dose-dependent manner. The Drosophila flies overexpressing AgosCSP5 were significantly less susceptible to the insecticides, omethoate, imidacloprid and cypermethrin but not to deltamethrin and tau-fluvalinate, compared with control flies. The transgenic Drosophila flies exhibited an LC50 resistance ratio of 2.6 to omethoate, compared with control flies. Likewise, the mortality of the transgenic flies to imidacloprid and cypermethrin was significantly lower than that of the control flies (p < 0.01). Homology modelling, molecular docking and dynamic simulation supported the interactions and revealed a higher stability of AgosCSP5/insecticide complexes than AgosCSP5/semiochemical complexes. Our study demonstrates for first time the in vivo evidence for the involvement of CSP genes in insecticide resistance of crop insect pests and provides new insights of the newly discovered CSP-mediated insect resistance mechanism to insecticides.

Establish real-time monitoring models of cotton aphid quantity based on different leaf positions in cotton seedlings

Cotton aphids, Aphis gossypii glover, are major pest threats to cotton plants, leading to quality and yield loss of cotton. Rapid and accurate evaluation on the occurrence and quantity of cotton aphids can help precision management and treatment of cotton aphids. The occurrence rules of cotton aphids on different leaf positions in cotton seedling stage for two cultivars of cotton were studied. The quantity of cotton aphids in the whole cotton seedlings were predicted based on the single leaf cotton aphid quantity. The correlation analysis results showed that cotton aphids of single leaf were significantly and positively correlated with the infected time, the all leaves of the whole plant, the whole plant contained all leaves and branches. The variance analysis results showed that cotton aphids of single leaf were significant difference with the extension of infected time. Based on different leaf positions, monitoring models were constructed respectively. The modelling set’s determination coefficient of ‘Xinluzao-45’ was greater than 0.8, while ‘Lumainyan-24’ was greater than 0.6. The best monitoring leaf position was the third for ‘Xinluzao-45’, the sixth for ‘Lumianyan-24’. From the data analysis, we can realize that it is feasible to construct a monitoring model based on the occurrence of cotton aphid in one leaf in cotton seedling, and different cotton varieties have different leaf positions. This will greatly reduce the investment of manpower and time.