Journal publishes student's botanical pesticide research

RESEARCH has proven that botanical pesticides are effective in controlling diamondback moth on round cabbage.

This was confirmed through a study by Sandrina Malapa, a 2019 Year 4 Sustainable Tropical Agriculture student last year, who is expected to graduate with a Bachelor’s degree next month.

Her research, which was conducted under the supervision of her lecturer Kari Iamba, resulted in their joint paper Efficacy of selected plant extracts against diamondback moth (Plutella xylostella L.) on round cabbage in situ, being published in the Journal of Entomology and Zoology Studies (JEZS). 

Solomon Yoba, another student that Mr Iamba supervised also had his research published in another journal called the IOSR Journal of Agriculture and Veterinary Science. 

The diamondback moth (DBM), also known as cabbage moth, is one of the most destructive cosmopolitan insect pests of Brassicaceous crops such as cabbage, broccoli, cauliflower and mustards. 

Originally pesticides were used to kill them but reliance on chemicals as a control measure caused diamondbacks to develop resistance to many common chemicals. This is why researchers are looking to develop new biological and chemical controls as well as different planting methods to reduce the destruction caused by the moths. Some have gained special interest in Botanical extracts because they are locally abundant, cheaper to access, compatible with natural enemies, safer for human consumption and possess insecticidal properties.

The research paper stated that the application of leaf, flower, fruit and seed extracts from selected insecticidal plants resulted in larval mortality, oviposition deterrence and reduced feeding activity of diamondback moths on treated cabbage leaves. 

It said most botanical pesticides when used in combination with effective natural enemies, produced successful plant protection results in an Integrated Pest Management (IPM) program. 

The application of plant extracts is to develop a push-pull system that will reduce oviposition (the process of laying or shedding fully developed eggs) of insect pests and concurrently enhance parasitism by its parasitoids in crops. 

Various semiochemicals are involved in push-pull strategies which act as repellent or attractant volatiles to orchestrate pests and natural enemy populations. Pests can be ‘pushed’ out of the crop by repellents and deterrents, and natural enemies can be ‘pulled’ into the pervaded crop by foraging attractants ‘volatiles’ to suppress the pests. 

The purpose of the study was to test the repellent effect of Garlic (Allium sativum L.), Chili (Capsicum frutescens L.), and Seaweed extract on diamondback moths. 

It was hypothesized that the application of these selected plant extracts would lower the number of diamondbacks and deter them from feeding on cabbage leaves. 

The evaluation of leaf damage was tested on two parameters; defoliation and leaf area index (LAI). LAI is a measure of yield in leafy vegetables like cabbage while defoliation quantifies damage due to DBM. The K-K cross variety of cabbage was chosen as the host subject because it is a common leafy vegetable that is cultivated locally.

A total of 180 cabbage plants and a sum of 3888 DBM larvae were sampled during the experimental period from September 6-22, 2019. The selected plant extracts showed varying results when compared with the reference group (control treatment). Garlic extract deterred the red spider mite, Oligonychus coffeae, from ovipositing and repelled other Lepidopteran pests, including DBM. Garlic extract oil was quite effective at suppressing DBM egg hatch, however activity against larvae was generally less effective.

Chili extract treatment supported previous studies as a good control method of DBM due to its antifeedant and repellent properties. Cabbages treated with chili and other botanical extracts produced comparable yield. There was notable defoliation under control treatment due to the absence of barrier against feeding larvae of DBM.

Through the study it was found that Seaweed and Chili extracts are effective in controlling DBM. Interestingly, however, their mechanisms of control differ. Chili possesses insecticidal phytochemicals that act as effective repellent and deterrent of DBM. Seaweed extract on the other hand is absorbed by the plant through assimilation and the biostimulants present along with micronutrients enhance the physiological resistance of the plant against DBM. Both plant extracts are recommended to be used by famers and utilized in an IPM program to ensure better crop performance.

It was concluded that farmers are now aware of the adverse effects of continuous use of synthetic insecticides, hence are now resorting to botanical pesticides for use in crop protection. 

The authors thanked the Academic Crops Section of Department of Agriculture at PNG University of Natural Resources & Environment for their assistance in the research. 

Several UNRE staff have congratulated Mr Iamba for his initiative. 

Jaupo Minimulu of the Department of Forestry said: “Making students research projects (case studies, IT projects etc.) become publishable is the way to go. Year in year out our students are engaged in good real publishable projects. We’re also fortunate to have the UNRE Journal launched recently. We all can do much better. Congratulations Mr Iamba for getting these two papers published and also on your scholarship award. I wish you the best in your studies.”

JEZS is a Peer Reviewed International Open Access Journal which is abstracted in various reputed databases. The Journal provides the platform with the aim of motivating the students and personnel in all fields of entomology and zoology.