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Shrubs in Nara desert under cicada attack
INSECTS are unrivalled in their diversity of form and colour. There are many species, particularly those in the deep desert or forest which remain unattended with the result that little is known of their ravages, lifestyle, habits, preferred habitats and their ecological relevance for the complex environmental system they inhabit.
This year, unusual monsoon rains in the country, particularly in Sindh and Balochistan, led insurgence of some insect pests of economic importance especially armyworm which inflicted widespread damage to cotton crop in upper Sindh and southern Punjab and jowar (sorghum) and pulses in Balochistan. Excessive and prolonged monsoon rain also encouraged whitebacked plant hopper and leaf folder outbreak on rice crop in upper Sindh and the then Naseerabad division of Balochistan. Damage to cotton and paddy crop received attention both at provincial and federal levels so much so federal minister of food and agriculture alongwith officials of the concerned quarters visited the affected area to ascertain the reported damage. But following the monsoon rains, widespread insurgence of cicadas on shrubs specially on the tamarix in the desert of Nara, remain unattended by the quarters concerned, specially the forest department, Government of Sindh. Prior to attending the insurgence of cicadas in the desert, it would be proper to introduce the Nara desert to our readers.
Arid desert
Nara desert consists of loose sand dunes known as scrublands scattered between the southeastern boundary of the Thar and north-eastern boundaries of Cholistan. Nara is extreme arid area. Climatically the region is hot and dry where cold winter and very hot summer persists. The daily summer maximum temperature ranges from 39oC to 41oC and the winter range is 1oC to 22oC. Average rainfall is insufficient to sustain any agricultural crops. Hot dusty winds blow during the summer. There are bushy growths of vegetation having spines and thorns.
Common vegetaion includes tamarix, prosopis (kandi), acacia and zizyphus. However, amongst the shrubs tamarix is widespread and the major source of green canopy in the desert. The desert is spread over an area of about 23,000 square kilometres.
On the world map this desert area is known as summer breeding zone of the desert locust. Beside locust, other member of the local ecosystem are birds, mammals, reptiles, insects. and wildlife. However, among the species of insects of economic importance in Nara desert, besides locust, is cicada (Homoptera cicadidae). The cicadas are wrongly called locust. They are the largest of all the Homoptera as certain species reach a length of nearly 10 cm from head to the tip of wings; others are much smaller. Their bodies are wedge shaped, the heads are broad and eyes bulging at the sides.
The cicadas are best known from the loud shrill calls made by the males; the females have no sound making apparatus. This is why it is said that “Happy are cicadas’ lives. For they all have voiceless wives.” Another noteworthy things about the cicada is the very long life of the young. One North American species, the periodical cicada, is also known as the seventeen-year locust. It spends 13 to 17 years as a slowly growing nymph underground, sucking sap from the roots of trees. After this long subterranean existence, it emerge in the form of winged adult. The species of cicada found here is the common Platypleura capitata oliv.
The present resurgence of cicada in the Nara desert, specially on the tamarix shrub, may be a new record and thus deserve to be taken into account by the concerned quarters. According to a federal Plant Protection Deparment source, in 1989, apple orchards at Khanzai in Quetta valley was invaded by the cicadas so severely that Agriculture Extension Department of the provincial government asked for aerial spray against this pest.
Review of literature on this species indicates that unprotected fruit trees sometimes have had as many as 9 per cent of the terminal buds destroyed by this pest. The injury is caused rather by the female cicada depositing her eggs in the twigs.
Following the rains in the desert, climatic condition had become conducive for the local resurgence of desert locust but no significant resurgence was recorded in the Nara desert as per locust wing of the Central Plant Protection Department.
Unprotected fruit trees sometimes have had as many as nine per cent of the terminal buds destroyed by this pest. The injury is caused by the female cicada depositing her eggs in the twigs than by the insect chewing them.
A survey of the Nara desert undertaken by this writer during the month of July and August 2003 indicates that excessive monsoon rain this year had allowed a mass emergence of cicada. The population of adult cicada was in swarms on the shrubs specially on the tamarix. The shrill calls made by swarming population of cicada at certain pockets were so loud and intense that it was difficult to talk.
Since emergence of cicada is almost entirely reliant on rainfall, impact of large-scale emergence of this pest on tamarix shrub canopy specially extent of damage of twigs following vigorous egg laying requires to be investigated by the forest department government of Sindh. This is because tamarix is the major shrub species which provides green canopy to the desert.
It would be pertinent to mention here that cicadas, besides inflicting some damage to trees, also provide a bountiful supply of food for the birds, predatory mammals, reptiles, spiders, etc, during the warmer months of the year.
The writer
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