Evaluation of insect CAP2b analogs with either an (E)-alkene, trans- or a (Z)-alkene, cis-Pro isostere identifies the Pro orientation for antidiuretic activity in the stink bug

Molecular targets for the development of new acaricides against Rhipicephalus microplus: a review

The cattle tick Rhipicephalus microplus is an ectoparasite with high economic importance to bovine culture, mainly in tropical and subtropical regions. The resistance of the tick from the commercial acaricides has hindered its control, thus motivating the search for new strategies. The purpose of this study was to perform a critical review about the main molecular targets of R. microplus that are useful for the discovery of new acaricides. Bibliographic search was conducted in the databases PubMed, ScienceDirect and CAB Direct, using the following descriptors: ‘Rhipicephalus microplus’, ‘Boophilus microplus’, ‘molecular targets’ and ‘action’, published between 2010 and 2021. Out of the 212 publications identified, 17 articles were selected for study inclusion. This review described 14 molecular targets and among these 4 are targets from commercial acaricides. Most of them are enzymes to catalyse important reactions to tick survival, related to energetic metabolism, mechanisms of biotransformation and neurotransmission. The data will be helpful in the development of new more effective and selective acaricides.

Conformational analysis of a cyclic AKH neuropeptide analog that elicits selective activity on locust versus honeybee receptor

Neuropeptides belonging to the adipokinetic hormone (AKH) family elicit metabolic effects as their main function in insects, by mobilizing trehalose, diacylgycerol, or proline, which are released from the fat body into the hemolymph as energy sources for muscle contraction required for energy-intensive processes, such as locomotion. One of the AKHs produced in locusts is a decapeptide, Locmi-AKH-I (pELNFTPNWGT-NH₂). A head-to-tail cyclic, octapeptide analog of Locmi-AKH-I, cycloAKH (cyclo[LNFTPNWG]) was synthesized to severely restrict the conformational freedom of the AKH structure. In vitro, cycloAKH selectively retains full efficacy on a pest insect (desert locust) AKH receptor, while showing little or no activation of the AKH receptor of a beneficial insect (honeybee). Molecular dynamic analysis incorporating NMR data indicate that cycloAKH preferentially adopts a type II β-turn under micelle conditions, whereas its linear counterpart and natural AKH adopts a type VI β-turn under similar conditions. CycloAKH, linear LNFTPNWG-NH₂, and Locmi-AKH-I feature the same binding site during docking simulations with the desert locust AKH receptor (Schgr-AKHR), but differ in the details of the ligand/receptor interactions. However, cycloAKH failed to enter the binding pocket of the honeybee receptor 3D model during docking simulations. Since the locust AKH receptor has a greater tolerance than the honeybee receptor for the cyclic conformational constraint in vitro receptor assays, it could suggest a greater tolerance for a shift in the direction of the type II β turn exhibited by cycloAKH from the type VI β turn of the linear octapeptide and the native locust decapeptide AKH. Selectivity in biostable mimetic analogs could potentially be enhanced by incorporating conformational constraints that emphasize this shift. Biostable mimetic analogs of AKH offer the potential of selectively disrupting AKH-regulated processes, leading to novel, environmentally benign control strategies for pest insect populations.

Assessment of insecticidal effects and selectivity of CAPA-PK peptide analogues against the peach-potato aphid and four beneficial insects following topical exposure

BACKGROUND

Insect Capability neuropeptides (CAP2b/CAPA-PKs) play a critical role in modulating different physiologies and behavior in insects. In a previous proof-of-concept study, the CAP2b analogues 1895 (2Abf-Suc-FGPRLamide) and 2129 (2Abf-Suc-ATPRIamide) were reported to reduce aphid fitness when administered by injection. In the current study, the insecticidal efficacy of 1895 and 2129 on the peach potato aphid Myzus persicae was analyzed by topical application, simulating a spray application scenario in the field. Additionally, the selectivity of the tested analogues was evaluated against a selection of beneficial insects, namely three natural enemies (Adalia bipunctata, Chrysoperla carnea and Nasonia vitripennis) and a pollinator (Bombus terrestris).

RESULTS

Within 3-5 days post topical exposure of aphids to 1895, higher mortality (33%) was observed, as was the case for the treatment with 2129 (17%) and the mixture of 1895 + 2129 (47%) compared to the control (3%). 1895 and the mix 1895 + 2129 showed the strongest and comparable insecticidal effects. Additionally, surviving aphids treated with 1895 showed a reduction in total lifetime reproduction (GRR) of 30%, 19% with 2129 and 39% with the mix 1895 + 2129. Of interest from a biosafety perspective is that by using the same delivery method and dose, no significant effects on survival, weight increase and food intake was observed for the representative natural enemies and the pollinator.

CONCLUSION

This study highlights the potential of exploiting CAP2b analogues such as 1895 (core structure FGPRL) as aphicides. Additionally, the CAP2b analogues used in this study were selective as they showed no effects when applied on four representative beneficial insects.

Insect capa neuropeptides impact desiccation and cold tolerance

The success of insects is linked to their impressive tolerance to environmental stress, but little is known about how such responses are mediated by the neuroendocrine system. Here we show that the capability (capa) neuropeptide gene is a desiccation- and cold stress-responsive gene in diverse dipteran species. Using targeted in vivo gene silencing, physiological manipulations, stress-tolerance assays, and rationally designed neuropeptide analogs, we demonstrate that the Drosophila melanogaster capa neuropeptide gene and its encoded peptides alter desiccation and cold tolerance. Knockdown of the capa gene increases desiccation tolerance but lengthens chill coma recovery time, and injection of capa peptide analogs can reverse both phenotypes. Immunohistochemical staining suggests that capa accumulates in the capa-expressing Va neurons during desiccation and nonlethal cold stress but is not released until recovery from each stress. Our results also suggest that regulation of cellular ion and water homeostasis mediated by capa peptide signaling in the insect Malpighian (renal) tubules is a key physiological mechanism during recovery from desiccation and cold stress. This work augments our understanding of how stress tolerance is mediated by neuroendocrine signaling and illustrates the use of rationally designed peptide analogs as agents for disrupting protective stress tolerance.