Pests of Melongene (Eggplant or Aubergine or brinjal) Solanum melongena, in Trinidad and Tobago.

Name of Pest: White flies (Bemisa tabaci):

“White flies are soft-bodied winged insects about 1/12 of an inch and are mostly active during the daytime”(Solomon 2014). They are of the Insect order‎ ‎Hemiptera and the family Aleyrodidae. They damage crops by sucking the cell sap from plants, reducing the turgidity of the plant, which decreases its ability to stand, despite the lack of a skeletal structural framework that animals have. They hence become weaker and unable to carry out photosynthesis. They can also cause indirect damage when there is an accumulation of honeydew after piercing and sucking, which then causes mold growth on foliage (Onstad 2014). They are also vectors in the transmission of plant viruses. Solomon also states that “White flies usually occur in groups on the undersides of leaves.” The females can produces up to 400 eggs.

Field Symptoms assisted in diagnosis:

•          Mottling of leaves and stunted new growth
•          Sooty mold growth on upper leaf epidermis
•         Yellowing of leaves
•          Eventual leaf death and in extreme cases plant death (heavy infestations).

N.B. - They can been visibly seen on the underside of leaves showing the field symptoms stated above, if leaves are turned over. They can also be seen flying around if the leaves are disturbed in both mild to severe infestations.

Suitable Management practices:

Cultural Control:

-      Removal of infested leaves

-      Vacuuming adults, or hosing down with water sprays (overhead irrigation also).

-      Aluminum foil or reflective mulches both repel white flies from vegetable gardens

-      The use of yellow sticky traps can aid in monitoring the pest populations and well as reducing it.

-      Insecticidal soaps, such as blue soap.

-      Never allow weeds and host plants to grow in greenhouse or in open field during non-crop periods.

-         Use of barrier broad leaf plants around greenhouse and kitchen gardens to further limit infestation risk.

Biological Control:

Predatory mites as well as Entomopathogenic agents such as nematodes and fungi (CABI 2014).

Chemical Control: use of Neonicotoids can be used prior to the flowering stages (Imidacloprid) and the rotation of products with less residual activity within plants can be used at the production stage of plants, which offer more repellent activity (Neem oil insecticides).

Image 1: Curled appearance of leaf surface indicating sign of sucking insect underneath



Image 2: White flies seen on the underside of leaf.




Image 3: Mold growth seen on leaf surface due to white fly damage to leaf underside in severe infestations.

Name of the pest: Thrips

Thrips are tiny insects with fringed wings, belonging to the order of insects known as Thysanoptera. They have rasping and sucking mouth-parts which abrasion the epidermal tissue of plant parts, where they then feed on the cell contents, which results in the stippling and discolored flecking (silvering) of the leaf surface. Pest species discolor and scar leaves, flowers, and fruit surfaces, and distort plant the growth. They are about as fat as a sewing needle and their distribution is worldwide, with many species affecting a wide range of Agricultural and non-agricultural crop species. However, their damage can be much worse when act as vectors and transmit viruses to plants. When eggs hatch they develop through two actively feeding larval stages and two non-feeding stages, the pre-pupa and pupa, before becoming an adult (UC IPM 2019). “Thrips palmi, which is known as Melon thrips, are a species that affect melongene production and was recorded in Trinidad during 1989” (CABI 2020). This species is not host specific affecting crops of other families.

Field Symptoms assisted in diagnosis:

•       Leaves become papery and distorted
•       Leaves develop tiny pale spots (stippling) and drop prematurely.
•       Infested terminals may become discolored, rolled and severe stunting to the early season flush of terminal growth
•       Deformed flowers, which may never open and eventually drop
•       Scarring of young fruits which mature and develop with scars on the fruit surfaces

Suitable Management practices:

Biological Control:

-      Predatory thrips, mites, and certain parasitic wasps help to control plant-feeding thrips (UC IPM 2019).

Cultural Control:

• Avoid planting susceptible plants next to these areas, and control nearby weeds that are alternate hosts of pest thrips.
• Keep crops well irrigated.

•  Avoid excessive applications of nitrogen based fertilizer, which may promote higher populations of thrips (UC IPM 2019).
•  Removal of old spent flowers which can harbor thrips and their disposal is recommended.

Chemical Control: 

The use of systemic insecticides such as Imidacloprid at first soil drench, which gives plants 6-8 weeks of protection before production stages. Neem oil and Abamectin have also been used to good effect to control thrips and are less toxic to beneficial insects.

                        A                                                          B

Image 4: 'A' displays signs of early damage or very little damage caused by thrips. 'B' displays thrips damage that is more significant and has caused stunted fruit growth.

                                          Video 1: Thrips found inside of a Melongene flower.

Name of the pest: Gall Midge

They belong to the insect family Cecidomyiidae and the insect order Diptera. Midges are tiny flies, which are about the size of gnats. Their larvae feed inside unopened flowers, resulting in misshapen flowers, damaged petals, thus preventing flowers from opening, which reduces overall crop yields. Flowers that fail to open may drop to the ground. The larvae feed on plant tissue, forming swollen masses or distortions, hence the name Gall midges. The larvae no more than one-twelfth inch in length, and pupate into the adult, in the soil within the root zone of crop.

Field Symptoms assisted in diagnosis:

-          A tiny hole on the flower receptacle is seen, which signifies where the adult female penetrates and deposits her eggs.

•            Flower buds infested by larvae remain closed and fall prematurely.
•           In early stages of attack, flowers can be infested with gall midge larvae.
•           Late stages of the attack fewer larvae are seen, even when flowers have fallen, this signifies that some larvae have already entered into soil to pupate into the adult stages.

Suitable Management practices:

Cultural and Mechanical control:

•           Removal and destruction of deformed flowers
•          Harrowing field of field, which exposes larva to both sun and predators.

Biological Control:

The use of Parasitoids (Kumar 2010).

Chemical control:

-        The use of soil applied insecticides works against the larvae that are ready to pupate. The insecticides with the active ingredient: imidacloprid (Commando or Protector), is effective against the midges when applied to the soil at planting. Apply contact insecticides during the late afternoon when adults are most active (Active ingredients such as Deltamethrin or Alpha-cypermethrin).

 

Image 5: Melongene flower with typical gall shape which shows larva damage and hole on receptacle (flower base), where female has deposited eggs.




Image 6: Melongene flower with larva of gall midge, which have fed and has caused rotting within.

                                           Video 2: Midge larva inside flower.

Name of Pest: Eggplant Fruit and Shoot Borer (Leucinodes orbonalis)

Belongs to the family Crambidae and the order Lepidoptera, which includes, butterflies and moths. The eggplant fruit and shoot borer is a pest that can lower yields in fields by piercing fruits after emergence from the eggs. Larvae feed on fruits, and losses can be as high as 100%. Adult moths fly in from adjacent fields or infested debris and deposit eggs on new leaves. When caterpillars are fully grown they enter soil or plant debris to pupate into the adult moth.

Field Symptoms assisted in diagnosis:

•         The first symptoms of infestation wilting of fresh younger shoots.
•          Holes on fruits can also be seen, where larvae can be seen.

Suitable Management practices:

Cultural and Mechanical control:

•          Crop sanitation: this involves includes cutting, removing and destroying damaged shoots until the final harvest. Crop residues cans also be uprooted and destroyed, killing eggs and larvae.
•         Grow seedlings under nylon netting to prevent moths from laying eggs on the plants.
•          Harrowing of the field to exposes larvae to sunlight which kills them and prevents pupation (CABI 2018).           
•       Pheromones to trap male moths have been used in Southern Asian countries.
•           Using tolerant varieties: Varieties that produce fruit that are more round-shaped have been known to have a higher tolerance. (CABI 2018).

Biological control:

-       Conservation of natural predators, that pray on larvae; Ants, pray mantis, ladybird beetles and avoid the usage of broad spectrum insecticides and more highly toxic insecticides. The use of Bacillus Thuringiensis insecticides: Bacillus Thuringiensis var. kurstaki (Products: Dipel, New BT 2X etc.) and Bacillus thuringiensis subspecies aizawai (Xentari) specialized for Lepidopteron species of caterpillars that work as stomach poisons when they feed on fruits.

Chemical control:

-        The use of systemic insecticides can also be used once fruits are safely harvested (Thiovin and Emavap have been successfully used in Trinidad).

  

Image 7: Fruit on tree with hole showing the signs of Melongene fruit borer.



Image 8: Fruit cut open showing where the borer has entered and fed. No larva was found.

Name of Pest: Leaf Miners

According to the Merriam Webster Dictionary leaf miners are: “any of various small insects (such as moths or Dipteran flies) that in the larval stages burrow in and eat the parenchyma of leaves. These insect pests are known to cause a variety of damage, including pale blotches and tunnels on plant leaves as the larvae travels and feeds. During heavy infestations, leaf desiccation and premature fall can occur. In melongene the damage is cosmetic, but according to can also create entry points for plant pathogens.

Field Symptoms and assisted Diagnosis:

-          Winding clear trails are seen on leaves in early damage, feed and tunnel throughout leaves. The larvae can be seen during the early damage. Older trails are darker, which come from the fecal matter of the larvae as well as secondary infections caused by fungi and bacteria, which can cause yellowing and desiccation of leaves which will then become detached from the plant.

Suitable Management practices:

Cultural Control:

•           Removal and proper disposal of previous crops
•           Removal of damaged leaves, which are first seen

Biological Control:

-          Conservation of natural predators that pray on larvae; such as wasps and avoid the usage of broad spectrum insecticides and more highly toxic insecticides.

Chemical control:

Use of systemic insecticides and insecticides with translaminar movement which kills larvae within leaves. At productive stages of crops, repellent insecticides and contact insecticides (pyrethroids) can be used to control and prevent adults from depositing eggs in field.



Image 9: Early signs of Leaf miner damage




Image 10: More damage seen on leaves: clearer tunnels are newer tunnels, the darker tunnels are older tunnels (possibly with fecal matter and secondary microbial infections).




Image 11: Yellowing of leaf, sign of infestation, will lead to leaf drop or further desiccation.

Other Pests of Melongene in Trinidad are:

Mollusks (Giant African Snail etc.), Mites, Caterpillars and Lace wing Bugs etc.

References:

David W. Onstad. 2014 “IPM and Insect Resistance Management.” Insect Resistance

Management- Biology, Economics, and Prediction Book (Second Edition).

Leevum A. R. Solomon. 2014 “WHITEFLY” Accessed 17^th March 2019.https://

archives.newsday.co.tt/2014/08/31/whitefly/

UC IPM. 2019. “How to Manage Pests: Pests in Gardens and Landscapes.” Agriculture 

and Natural Resources, University of California: http://ipm.ucanr.edu/PMG/PESTNOT

ES/pn7429.html.

Jackie Caroll. 2018. “Blossom Midge in Plants: How To Control Midge Pests In Flow

er Buds.”Accessed: 13^th March 2020. https://www.gardeningknowhow.com/plant-problems/pests/insects/blossom-midge-in-plants.htm.

Kumar, N. K. Krishna H. R., Ranganath, Ramasamy Asokan, Chandrashekara Kn Re

bijith K B and Tejavathu Hatiya Singh. 2010 “Gall insects damaging eggplant and b

ell peppers in South India.” Accessed: 17^th March 2014.https://www.researchgate.nt

/publication/221966492_Gall_insects_damaging_eggplant_and_bell_peppers_in_So

uth_India.

CABI. 2018. “Plantwise Knowledge Bank: Melongene fruit and Shoot Borer.”

Accessed: 13^th March 2020. https://www.plantwise.org/KnowledgeBank/pmdg/20

187800468.

CABI 2020. “Invasive Species Compendium: Thrips palmi (melon thrips).” Access

ed: 13^th March 2020. https://www.cabi.org/isc/datasheet/53745.

CABI 2020. “Invasive Species Compendium: Bemisia tabaci (tobacco whitefly)” Ac

cessed 17^th March 2020. https://www.cabi.org/isc/datasheet/8927.

Acknowledgements:

The Videos and Pictures were taken from farmers of the Orangre grove and Heights of Guanapo (in Arima). Special thanks must be given to the farmers who volunteered in this exercise.