Whitefly and black aphid: a threat to cashew and coconut trees in southeastern Bahia

Along the coast between the municipalities of Ilhéus and Canavieiras-BA, it is common to see cashew trees (Anacardium occidentale L) heavily attacked and/or dead as a result of injuries caused by whiteflies (Figure 1). They are called that because they have wings that resemble a small fly (Figure 2). In fact, these are insects from the Hemiptera order belonging to the Aleyrodidae family. It is possible that Aleurodicus cocois (Martin, 2008) is the same species that occurs on cashew trees in the state of Ceara.

In addition to the depletion and subsequent death of the cashew tree due to continuous sap sucking, these insects excrete sugars (also called honeydew). The deposition of honeydew on the plant can provide a favorable substrate for the development of fungi that cover the plant, forming sooty mold that affects the processes of photosynthesis and leaf respiration (Lazzari & Carvalho, 2009). The occurrence of whiteflies on cashew trees is more frequent in summer or during dry periods.

Although the whitefly attacks cashew trees more, in the south of Bahia it also attacks coconut trees, according to observations carried out in some regional municipalities, mainly on the trees close to cashew trees that have previously suffered injuries. Coconut trees, when attacked by whiteflies, have a whitish gray leaf crown (Figure 4) as a result of a waxy white layer and countless elongated, translucent, sugary threads that dissolve when touched (Ferreira et al., 2011). The entire life cycle of the whitefly is

in the coconut tree whose posture, in general, occurs on the lower side of the leaflet (figure 3). Some whiteflies have a reproductive capacity of 100 to 300 eggs/female, and multiply quickly, producing up to 16 generations per year (Ferreira et al. 2011).

According to reports from owners of residential areas on the regional seafront, the productivity of coconut trees dropped significantly after the fly attack. In Ceara, in the municipality of Paracuru, the whitefly attack reduced the productivity of coconut trees by 35%.

The whitefly is a transmitter of several diseases of viral origin in other cultures, however, to date there is no record in Brazil of this association with the coconut tree.

The black coconut aphid (Figure 5) Cerataphis lataniae Boisduval, 1867 (Hemiptera: Aphididae) is a black aphid, circular in shape and surrounded by a white fringe, with a diameter varying between 1,5 and 2,0 mm, with slow locomotion , it attaches itself to a certain point on the plant to suck the sap. In saffreiro coconut trees, it causes abortion of female flowers, falling of small fruits and developing fruits (Ferreira&Filho). They are generally located on the lower part of the leaflets of the youngest leaves of young and adult coconut trees.

In commercial plantations of dwarf coconut trees in the municipality of Una, BA, it has been observed that injuries caused by C. lataniae significantly reduce productivity and depreciate the commercial value of the fruits due to the deposition of sooty mold on them. Field studies revealed that coconut trees heavily attacked by the black aphid can present 4.378 aphids on the leaflets on a single leaf rachis.

Considering that foliar diseases, blight (Lasiodiplodia theobromae; Botryosphaeria cocogena) and sandpaper (Catacauma torrendiella) are present in coconut trees in southern Bahia, the occurrence of this insect will increase damage to the crop, especially in relation to productivity.

Furthermore, these insects, like whiteflies, excrete honeydew that attracts and serves as food for several species of insects, including the pixixica ant (Wasmannia auropunctata, Roger, 1863). The flow of pixixica along the stem of the coconut tree causes injuries to workers involved in collecting the fruits and, as a result, many workers refuse to work in coconut trees where this ant is present.

Aphids are easily controlled when coconut trees are low. Once high, control is inefficient due to the barrier formed by older leaves that prevent pesticides from adhering to younger central leaves, where aphids prefer to colonize. In the case of hybrid coconut trees (dwarf x giant) over twenty meters tall, it is practically impossible to spray using atomizers. Furthermore, the majority of coconut plantations located on the coast of the state of Bahia are formed by small producers who do not make use of technological adoptions, due to cultural values ​​and low purchasing power.

Whiteflies on young (small) coconut trees can be controlled with a mixture of 2% crude cottonseed oil and 1% detergent. However, this mixture proves to be inefficient when coconut trees are tall. Ferreira et al., (2011) mention that even synthetic insecticides, when delivered with appropriate equipment, need to be mixed with silicone adjuvant spreaders for better absorption and penetration of the product, as strong winds close the leaflets when wrapping the leaves, making it difficult for the spray to adhere. insecticide.

Therefore, it is practically impossible to control black aphids and whiteflies through spraying, when it comes to very tall plantations. Add to this problems of drift due to strong northeast winds in the summer season.

The use of imidacloprid injection is already common practice in some countries. In Australia, an injection of 20% imidaclorpid was used to combat the stink bug Thaumastocoris peregrinus Carpinteiro & Dellapé 2006, on eucalyptus plantations in urban areas (Noak, 2009). The aphid Adelges tsugae Annand, a severe pest of spruce (Tsuga spp) in the United States, has been efficiently controlled with 5% imidacloprid injection (Doccola et al.; 2007).

In the case of tall coconut trees established in small areas, there is no more efficient and economical tactic than injecting the coconut tree stem with imidacloprid. To execute it, a hole is made with the help of a drilling machine at the base of the coconut tree stem. Afterwards, the recommended amount of insecticide is injected and then the hole is covered with a dowel or lime putty.

Imidacloprid belongs to the group of neonicotinoids, has systemic action, blue band and has low toxicity for mammals. It can be applied via foliar spray, trunk injection or brushing, soil injection and through watering or irrigation. However, there are reports in the literature citing imidacloprid as extremely toxic to bees when applied via spraying.

Injection of 25% imidacloprid was efficient in controlling the black aphid on coconut trees at the Lemos Maia Experimental Station (Esmai) belonging to the Cocoa Farming Executive Committee (Ceplac). In an area where all coconut trees were attacked by aphids, it was observed that the coconut tree that received a dose of 10 ml of 25% imidacloprid had very green leaflets (Figure 6 A), compared to those of the coconut tree next door (B) which he did not receive. However, it is necessary to study dose/efficiency in order to identify a minimum quantity with maximum efficiency on the black aphid. With one liter of 25% imidacloprid it is possible to treat 2,5 hectares of coconut trees.

Imidacloprid injection appears to be a low environmental impact tactic, as it apparently does not affect organisms on foliage and soil. However, the level of contamination of this insecticide on coconut tree pollen and nectar is unknown. Another aspect observed in relation to imidacloprid is its slow action at the beginning of treatment. It is also worth noting that imidacloprid had no effect on the necrosis mite Aceria guerreronis. Related to sooty mold, the fungus only detaches from the leaflets after heavy rain.

Imidacloprid is not registered with the Ministry of Agriculture and Livestock (MAPA) for the control of black coconut aphid. Therefore, it cannot be used or sold for this purpose. Therefore, in the state of Bahia, its use under any circumstances is subject to prior consultation with the Bahia State Agricultural Defense Agency (ADAB). It is recommended that residual levels of this insecticide in coconut and copra water be determined, as once known, mechanisms can be sought to register it with MAPA.