Behavioural Interpretations of the HPLC Peaks Derived from Egg-Pod Foam Extracts of the Desert Locust Schistocerca gregaria (Forskål)

Aims: The present study was aimed at assessing the bioactivity of the HPLC fractions and peaks from egg-pod materials of the crowd-reared desert locust Schistocerca gregaria (Forskål) (Orthoptera: Acrididae) that elicited gregarious behaviour in the first-instar hatchlings derived from treated eggs of solitary-reared insects.
Study Design: In a series of stepwise experiments using crude extracts of the egg-pod materials in different solvents, filtered foam-extracts, HPLC foam-extracts and their fractions, sub-fractions and peaks, bioactivities of the egg-pod foam of the crowd-reared locusts have been assessed in terms of behavioural gregarization in the hatchlings from treated solitary eggs.
Place and Duration of Study: The initial experiments were carried out in the Departments of Zoology and Chemistry, University of Oxford, UK, during January 2002 and May 2003. Further analyses, manuscript writing and updated interpretations were performed in the Laboratory of Genetics and Molecular Biology, Department of Zoology, University of Rajshahi, Bangladesh, during September 2012 and February 2013.
Methodology: Beginning with egg-pod wash and foam-extracts in ethanol, hexane and water, step-wise bioactivities of the filtered foam-extracts, HPLC foam-extracts, HPLC fractions, sub-fractions and their peaks were assayed in terms of behavioural gregarization of the hatchlings from treated solitary eggs. Behavioural assays and multiple logistic regressions (LR) analysis were used to determine the behavioural phase state in terms of median Probability (solitary) values of individual experimental hatchlings.
Results: It has clearly been demonstrated that filtered foam-extracts at the concentrations of 0.1 foam-plug equivalent (FPE) and their HPLC reconstitutes at 0.2-0.4 FPEs significantly shifted the behavioural phase of the treated solitary hatchlings towards gregariousness. Further fractionations of the HPLC foam-extract at 0.4 FPE reconstitutes into four fractions (Fraction 1-Fraction 4), four sub-fractions (Fraction 3.1-Fraction 3.4), three sub-fractions of Fraction 3.2 (Fraction 3.2.1-Fraction 3.2.3) and five peaks (peak 1-peak 5) of the sub-fraction 3.2.2 revealed that peak 3 contained substances that induced the maximum behavioural gregarization in the hatchlings from treated solitary eggs.
Conclusion: HPLC reconstitutes of the aqueous egg-pod foam-extracts of the crowd-reared S. gregaria are capable of shifting the behavioural phase of the treated solitary hatchlings towards gregariousness. Further fractionations of the HPLC foam-extracts into sub-fraction 3.2.2 and five peaks revealed that peak 3 contained bioactive substances that elicited maximum gregarizing behaviour in the hatchlings from treated solitary eggs. The results deserve further investigation with regard to determining the precise nature of the causal factor(s) that escaped NMR’s detection thresholds in an earlier study.