Melaleuca quinquenervia (Cav.) S.T. Blake (Myrtales: Myrtaceae): Natural alternative for mosquito control

Biocontrol efficacy of cajeput oil against Anopheles stephensi L. mosquito and its effect on non-target species

Chemical insecticides are effective at controlling mosquito populations, but their excessive use can pollute the environment and harm non-target organisms. Mosquitoes can also develop resistance to these chemicals over time, which makes long-term mosquito control efforts challenging. In this study, we assessed the phytochemical, biochemical, and insecticidal properties of the chemical constituents of cajeput oil. Results show that Melaleuca cajuputi essential oil may exhibit mosquito larvicidal properties against Anopheles stephensi larvae (second-fourth instar) at 24 h post-treatment. At 24 h post-exposure, the essential oil resulted in a significant decrease in detoxifying enzymes. All of these findings indicate that cajeput oil infects An. stephensi larvae directly affect the immune system, leading to decreased immune function. Cajeput oil significantly affects the second, third, and fourth instar larvae of An. stephensi, according to the bioassay results. Cajeput oil does not induce toxicity in non-target Eudrilus eugeniae earthworm species, as indicated by a histological study of earthworms. Phytochemical screening and GC-MS analysis of the essential oil revealed the presence of several major phytochemicals that contribute to mosquito larvicidal activity. The importance of cajeput oil as an effective candidate for biological control of the malarial vector An. stephensi is supported by this study.

Larvicidal Potential of Caribbean Plants

Mosquitoes are vectors for numerous arboviruses such as dengue, chikungunya, and Zika which continue to negatively impact the health of Caribbean populations. Within the region, synthetic insecticides are primarily used to control mosquito populations. In many countries however, these compounds are becoming less effective due to resistance, and they may also be harmful to the environment. Thus, there is a significant need for the development of alternative agents to combat the mosquito threat in the Caribbean. Worldwide, botanical-based products are being increasingly investigated for vector control because they are environmentally friendly and are often highly effective mosquitocidal agents. Although the botanical diversity within the Caribbean is remarkable, work on plant biopesticides in the region remains limited. The aim of this review, therefore, is to discuss the use of Caribbean botanical extracts as larvicidal agents. Additionally, we highlight the need for future work in this area which may subsequently lead to the implementation of transformative public health policies.

Myrtaceae in Australia: Use of Cryobiotechnologies for the Conservation of a Significant Plant Family under Threat

The Myrtaceae is a very large and diverse family containing a number of economically and ecologically valuable species. In Australia, the family contains approximately 1700 species from 70 genera and is structurally and floristically dominant in many diverse ecosystems. In addition to threats from habitat fragmentation and increasing rates of natural disasters, infection by myrtle rust caused by Austropuccinia psidii is of significant concern to Australian Myrtaceae species. Repeated infections of new growth have caused host death and suppressed host populations by preventing seed set. Although most Myrtaceae species demonstrate orthodox seed storage behavior, exceptional species such as those with desiccation sensitive seed or from myrtle rust-suppressed populations require alternate conservation strategies such as those offered by cryobiotechnology. Targeting seven key Australian genera, we reviewed the available literature for examples of cryobiotechnology utilized for conservation of Myrtaceae. While there were only limited examples of successful cryopreservation for a few genera in this family, successful cryopreservation of both shoot tips and embryonic axes suggest that cryobiotechnology provides a viable alternative for the conservation of exceptional species and a potential safe storage method for the many Myrtaceae species under threat from A. psidii.

Larvicidal activity of plants from Myrtaceae against Aedes aegypti L. and Simulium pertinax Kollar (Diptera)

INTRODUCTION:

Despite their widespread usage, synthetic insecticides and larvicides are harmful for controlling disease-causing mosquitoes owing to the development of resistance. The leaves of Eugenia astringens, Myrrhinium atropurpureum, and Neomitranthes obscura were collected from Marambaia and Grumari restingas. The safety and larvicidal efficacy of their extracts were tested against Aedes (Stegomyia) aegypti L. and Simulium (Chirostilbia) pertinax Kollar.

METHODS:

The dry leaves were subjected to static maceration extraction using 90% methanol. A. aegypti and S. pertinax larvae were exposed to 7.5, 12.5, and 25.0 µL/mL of the extracts (n= 30). The larvicidal activity after 24 h and 48 h, and the mortality, were determined. The median lethal concentration (CL₅₀) was estimated by a Finney's probit model.

RESULTS:

M. atropurpureum and E. astringens extracts exhibited the strongest larvicidal effects against A. aegypti. M. atropurpureum extracts (25 µL/mL) caused mortalities of over 50% and 100% after 24 h and 48 h, respectively (CL₅₀ = 11.10 and 9.68 ppm, respectively). E. astringens extracts (25 µL/mL) caused mortalities of 50% and 63.33% after 24 h and 48 h, respectively. High concentrations of N. obscura extracts induced a maximum mortality of 46.66% in A. aegypti larvae after 48 h (CL₅₀= 25 ppm). The larvae of S. pertinax showed 100% mortality following exposure to all the plant extracts at all the tested concentrations after 24 h.

CONCLUSIONS:

The extracts of M. atropurpuerum exhibited the strongest larvicidal activity against A. aegypti. The larvae of S. pertinax were sensitive to all the extracts at all the tested concentrations.

Chemical Composition and Behavioral Effects of Five Plant Essential Oils on the Green Pea Aphid Acyrthosiphon pisum (Harris) (Homoptera: Aphididae)

Essential oils (EOs) from Schinus molle, Helichrysum gymnocephalum, Cedrelopsis grevei and Melaleuca viridiflora, four aromatic and medicinal plants, are commonly used in folk medicine. EOs were characterized by gas chromatography/mass spectrometry (GC/MS) and quantified by gas chromatography-flame ionization detection (GC-FID); then evaluated for their behavioral effects on adults of the green pea aphid Acyrthosiphon pisum (Harris) using a Perspex four-armed olfactometer in order to test the compatibility of their use as phytoinsecticides to control this insect pest. Our results showed that the EOs from the leaves of S. molle, M. viridiflora and C. grevei did not change aphids' behavior. However, S. molle fruits EO seemed to be attractive while H. gymnocephalum leaves EO exhibited repellency towards aphids at a dose of 10 μl. The major compounds in S. molle fruits EO were 6-epi-shyobunol (16.22%) and d-limonene (15.35%). While, in H. gymnocephalum leaves EO, 1,8-cineole was the main compound (47.4%). The difference in aphids' responses to these two EOs could be attributed to the differences in their compositions. Our findings suggest that these two EOs have potential applications for the integrated pest management of A. pisum (Harris).