RICE DAMAGING WHITEFLY (Aleurocybotus indicus) 26/05/2022

Class: Insecta (insect).

Order : Hemiptera (half-winged).

 Suborder: Sternorryncha.

 Family: Aleurodidae (Whitefly).

Genus : Aleurocybotus.

Species: Aleurocybotus indicus (Former name: Vasdavidius indicus)

Whiteflywhitefly(Also: Whitefly ), due to a powdery coating on the body, the pest was first recorded on rice in 1966 in Santaram India and later in African countries: Senegal (1977), Nigeria, Niger, Mauritania, causing yield losses of up to 80%. In Vietnam, in the past, whiteflies were rarely found and caused damage on rice, only common on vegetables such as peppers, eggplants, melons, cucurbits, etc. In 2010, a large-scale pest was recorded in Long An, An Giang, Tay Ninh, infected area: 15,462 ha and now tends to spread in Mekong River Delta provinces and affect productivity.

Note: Rice whitefly, quite similar to guava whitefly (whiteflyAleurodicus dispersus/Hemiptera/Sternorrhyncha), cassavawhiteflywhitefly(Besimia tabaci/Hemiptera/Sternorrhyncha), but different Family: whitefly belongs to the Aleurodidae (whitefly), while guava and cassava whiteflies belonging to the white fly family. The durian jumping hopper (Allocaridara malayensis, belonging to the Psillid family ofwhiteflyjumping hopper), is uniformly winged (Homoptera).

Damages

Fields and rice affected by whiteflies

whitefly causes damage by sucking leaf sap, causing leaves to turn yellow (larvae), rough leaf surface (mosaic), leaves twisted or contorted, leaf neck shrunk (adult), if damaging at the flowering stage , the flag leaf is blocked, twisted, sowhiteflythat opened panicle can not come out , if it comes out , the rice grain will also be shriveled. This symptom is similar to viral leaf curl dwarfism, but virus has not been detected in twisted leaves (Mekong River Delta Rice Institute). Damage mainly in the tillering stage, at first it is just a small yellow bunch, then it spreads along with the growth of the population, if not treated and met with favorable conditions (hot sun), will accumulate. density and cause severe damage in the flowering-bootingwhiteflystage. The varieties Jasmin 85, IR 50404… are susceptible to infection. According to research by the Mekong Delta Rice Institute, experiments on varieties OM 4900, IR 4625, IR 64, at the period of 30whiteflyday after sowing, infected 30-40 heads/tiller, affecting yield, if the infestation density is 60 heads/tiller, the yield will be reduced from 23 to 31%, the damage can be greater if whitefly damages the flowering-booting stage. Due to the flowering stage, the pistil of ricewhiteflyis white, so it is easy to confuse with whitefly, on the other hand, the symptoms of rice leaf yellowing at this stage are also easily confused with early ripening yellowing or leaf edge burn , wrong diagnosis will cause more severe damage.

Because whiteflies have a relatively short life cycle (about 20-22 days), lay many eggs (100-200 eggs), eggs lay on the underside of leaves, spraying is difficult to contact, whiteflies develop and cause strong damage in hot weather. The long-term damage from tillering towhiteflyflowering-booting easily affect the yield, so it is necessary to visit the field regularly, detect it early and prevent it in timely manner

Biological characteristics

Life cycle – Eggs – whitefly

Whitefly is hemimetabolic .The life cycle lasts about 17-24 days (shorter than BPH), including 3 stages: Egg - larva - adult. Larvae have four instars , 4-instar-larva is pseudopupa

The adult has 2 pairs of white wings,whiteflyit is like a roof when perching, hiding in an airtight place, the average size: 0.98 mm/female and 0.83 mm/male, newly hatched, transparent adults. The wings are fragile, so they have weak flight power (half-wing / Hemiptera), then when the wings are dry, the body is covered with white powder, better flight power, when it is windy or disturbed, whiteflies fly out, whiteflies often hide and damage the underside of leaves.

Female adults lay many eggs: 100-240 eggs, eggs are laid sporadically or in streaks on the underside of leaves near the main veins, concentrated near the leaf apex, lined up like fish scales, eggs are elongated, newly laid ones have white color, eggs are about to hatch turns brown, the survival rate (eggs-larvae) is about 70%. Unisexual reproduction , produce the next generation of 100 male adults (Mekong Delta River Rice Institute).

Larvae are of thewhitefly3 instars. At the 1^st instar, there is no pollen, moving near the leaf veins or around to suck, less moving because the legs are not yet developed, lasting 3-4 days. The 2^nd instar : Molting, the body is covered with a thin layer of powder, clinging tightly to the leaf epidermis to suck, 2-3 days long. the 3 ^rd instar: the body changes little, does not move, is 2-3 days long, then molts to pseudopupaewhiteflythat have a hard shell, clinging to the leaf epidermis, after 2-4 days, the pupae fly out

The suitable temperature for leaf whiteflieswhiteflyis 30 degrees Celsius, living and causing damage are common in the dry season, hot weather, peak period of Ba Chang drought (July-August) in the southern provinces.

Eggs of whiteflies cling to the underside of leaves, are mosaic andwhiteflyear choking

Secondary host

 Chloris barbata,whiteflyDactyloctenium aegyptium.

Natural enemies

Whitefly has many natural enemies, such as Parasitic Bees (Encarsia japonica, E.sophia, E.transversa...), predatory natural enemies such as 8-dot ladybug (Harmonia octomaculata)...

Farming methods and whitefly population

- Varieties of Jasmin 85, IR 50404, Đài thơm 8, RVT... are susceptible to infection.

- Vareties OM 4218, IR 4625 sticky rice is less infected.

- Transplanted rice has a lower population of whiteflies than seeded rice.

- Thick sowing (150 - 250 kg/ha) gives higher numbers of whiteflies than sparse sowing (100 - 120 kg/ha).

- The rice crop in the rainy season has a lower population of whiteflies than in the dry season, because rainwater reduces the population of whiteflies.

- There was no relationship between water management in the field, weeds, straw and whiteflies population.

Detection

- Shake the foliage to see if whiteflies fly up or not

- Observe the cobwebs in the field, see if there are whiteflies attached to the cobwebs or not

- Observe the underside of rice leaves to see if there are whiteflies eggs laid along the leaf veins or not.

- Pay attention to rice from tillering stage to flowering-booting stage, check the rice fields with yellow leaf symptoms to determine if it is due to yellow dwarf disease, leaf curling dwarfism, premature yellowing of leaves, leaf edge burn or whitefly.

- Pay attention to the rice fields planted near the garden of guava, vegetables, melon, cassava ...

- Regularly visit the fields affected by whiteflies in the previous crop, pay attention to the fields of excessive nitrogen fertilization, late nitrogen fertilization, dense fields, early spraying of pesticides.

whiteflies attached to the cobwebs

Chemical products

- Research shows that chemical products based on Abamectin, Emamectin can control whiteflies 65-68%. Thewhiteflyproducts based on Pymetrozine (500g/kg) controlled 70.5 - 72.6% when observing 10 days after spraying (Mekong River Delta Rice Institute). In addition, other bases such as Imidacloprid, Acetamiprid also give good effect against whiteflies (CABI, IRRI).

- It should be noted that because the body of whiteflies (adults) is covered with a layer of white powder, the eggs are covered in a hard, waterproof wax layer, therefore contact products are not as effective as those with systemic, deep penetration and fumigant effects and it is necessary to mix it with an adhesive or SK Enspray 99EC mineral oil, in addition, spraying with the right technique also helps to increase the effectiveness of prevention.

Prevention and treatment

Apply integrated measures, including:

- Planting varieties resistant to whitefly, especially varieties with upright leaves.

- Sowing at the same time, without sowing, planting thickly.

- Fertilizer balance, reasonable, do not over-fertilize nitrogen, apply nitrogen late.

- Visit the field regularly, pay attention to the tilleringwhitefly, flowering booting stages, especially when the field is often damaged.

- The field is damaged early, can add Urea, DAP and Potassium fertilizers.

- If the population of whiteflies is high in the flowering-booting stage (10-40 whiteflies per 30-50 rice bushes), which is likely to cause yield damage, one of the following products can be used:

1. Pymetrozine (+ Nitenpyram) base: Osago 80WG, Sagometro 50WG

2. Dinotefuranwhitefly(+ Imidaclorpid) base: Brimgold 200WP.

3. Abamectin/Emamectin base: Binhtox 3.8EC or Comda gold 5WG

4. Chlorpyrifos methyl base: Sago super 20EC

5. In case of immediate need to suppress the epidemic, use Fenbis 25EC (high effective against mealybugs andwhiteflyhas fumigant property ), Sherzol 205EC or Sec Saigon 25EC

The above products need to be used alternately and should be combined with SK Enspray 99EC mineral oil to increase the effectiveness of prevention.

When spraying, pay attention

1. Should spray close to the surface of the rice leaves to kill whiteflies adults, spray evenly on both sides of the leaves, and at the same time point the nozzle low below the foliage so that the whiteflies can easily hit the product and kill the eggs attached to the underside of the leaves. Pay attention not to spray when the rice is blooming, if necessary, spray in the afternoon.

2. Adjust the spray nozzle to fine particles and spray the recommended amount of water-product.

3. It is recommended to add SK Enspray 99EC mineral oil (mixed dose: 50 - 60 ml of mineral oil/25-liter-tank) or an adhesive (adhesive Sago) to dispel the powdery layer and prolong the retention on the leaves.

4. Should be sprayed early in the morning (6-9 hours) because whiteflies are still wet, fly slowly, do not spray when it is windy or about to rain.

5. Should be sprayed simultaneously to limit the spread of whiteflies, moving from one field to the next.

6. If the rice is about to flower, and is affected by whiteflies, it is possible to add fertilizer containing Urea, DAP, and Potassium. If the rice is just flowering, it can be sprayed with foliar fertilizer.

References:

1. Plantwise Knowledge Bank, CABI, IRR82I

2. Mekong River Delta Rice Institute.

3. Doctoral Thesis of Vo Thi Bich Chi, Can Tho University of Agriculture, 2016.

4. Information of local sub-deparments.