**3. Discussion**

Schuhly et al. [13] reported β-elemene as the major compound in the fruit essential oil of *M. grandiflora* which corroborates the finding of this study having β-elemene (6–14%) in all the essential oils of *M. grandiflora* except seed oil. Guerra-Boone et al. [14] reported bornyl acetate (20.9%) as the major compound in *M. grandiflora* leaf oil, however, we did not detect this compound in the leaf oil. Garg and Kumar [15] reported β-caryophyllene as the major compound (34.8%) in flower essential oil whereas only a small amount (1.1%) was detected in the present study. Farag and Al-Mahdy [16] reported variation in the contents of *M. grandiflora* flower oil volatiles obtained through headspace and water distillation techniques indicating the effects of the isolation technique on the yield of different compounds. Such differences in chemical compositions of essential oils are expected and can be attributed to many factors including geographic location, genetic factors, climate, crop stage, harvesting time, and processing method [17,18].

In our previous studies, some of the compounds that were present in these essential oils exhibited very insignificant biting deterrence. α-Phellandrene (BDI = 0.52), (+)-α-pinene (BDI = 0.47), (-)-α-pinene (BDI = 0.41), (+)-β-pinene (BDI = 0.57), (-)-β-pinene (BDI = 0.51), *p*-cymene (BDI = 0.48), *trans-*sabinene hydrate (BDI = 0.61) showed biting deterrent activity lower than DEET. β-caryophyllene and caryophyllene oxide with BDI values of 0.54 and 0.66, respectively, were also significantly lower than DEET at 25 nmol/cm2 and these two sesquiterpenes also did not repel mosquitoes up to the highest dose of 1.5 mg/cm2 in cloth patch assay [6,19–22]. Hexadecanoic acid that was only present in seed essential oil was reported to have biting deterrence lower (PNB = 0.72) than DEET [23]. In our previous study, we found that mid-chain length acids (C10:0 to C13:0) showed the highest biting deterrent activity against Ae. aegypti as compared to short-chain length acids (C6:0 to C9:0) [22]. The current study reveals similar pattern of medium chain length fatty alcohol (C10:0) had higher biting deterrent activity than short-chain length alcohol (C8:0). However, we shall work on this hypothesis and confirm the activity toward short, med, and long-chain fatty alcohols. Many methylbutyrates present in the seed essential oil were tested in our screening program and found not active as biting deterrents (Ali personal communications). Since most of the major compounds that were present only in seed essential oil did not show any significant activity, 1-decanol might be the main compound responsible for the biting deterrent activity of *M. grandiflora* seed essential oil.

The toxicity of many natural compounds present in plant essential oils against mosquitoes has been reported in the literature. α-Pinene (LC50 = 49.5 ppm), β-pinene (LC50 = 35.9 ppm), β-caryophyllene (LC50 = 26.0 ppm), and caryophyllene oxide (LC50 = 29.8 ppm) were active as larvicides against *Ae. aegypti* whereas 1,8-cineole did not show any mortality at the highest screening dose of 125 ppm [19,23]. Monoterpenes that were present in variable concentrations in these essential oils showed larvicidal activity. These higher percentages of monoterpenes (α- and β-pinenes) in combination with other compounds may be responsible for the high toxicity of immature- and mature fruit essential oils. We will further explore other compounds present in *M. grandiflora* essential oils for their potential as larvicides against mosquitoes. Ethanolic extracts of sarcotesta of the seeds of *M. dealbata* were reported to have 96.4% mortality at 0.1 mg/mL against the Mexican fruit fly (*Anastrepha ludens* Loew) whereas the extracts from the other parts were inactive [24].
