Pests Affecting Mango and Mango Trees | Zoology

Here is a list of pests that damage mango and mango trees: 1. Mango Hoppers 2. Mango Mealy-Bug (Drosicha Mangiferae) 3. Mango Stone Weevil (Sternochetus Mangiferae).

1. Mango Hoppers:

The mango hoppers are the insects, which cause a humming noise and almost dart into your face once you happen to walk below a mango tree whose branches are not much higher than your height. This is too spectacular a phenomenon to be ignored particularly during the July- August period. These are the most serious pests of the mango tree.

These belong to the family Jassidae; hence their general characteristics are like those of the cotton jassids already described. The point which appears to be of special interest is that although there are three fairly important species Amritodua atkinsoni, Idioscopus clypealis and I. niveosparsus, these are still reported to be, unlike the mango mealy but, monophagous, i.e., feeding and breeding only on mango.

Like other jassids, they suck the plant- sap and due to this drain caused by a very large number of rather small individuals, the flower- buds, and flowers etc., first become flaccid and then wither and die. This affects the fruit-set very adversely and the young fruits fall off. Also like other jassids, they produce the sticky honeydew which encourages the development of sooty mould and which in turn not only gives a sickly look to the plant but also hinders the photosynthetic activities of the leaves which are covered with the sooty mould.

The size of the different species varies from about 4 mm. to about 6 mm. and there is considerable over-lapping in this character. Also, both the structure and the habits of the three species differ, only in slight and rather unimportant details. After spending winter in the adult stage, the mother- hopper lays eggs within the tissues of tender shoots, flower- buds, tender leaves, etc.

These eggs hatch within a period of one week or ten days. The nymphs soon after hatching begin to such the plant-sap. The nymph’s period is completed within two to four weeks only. Thus, there can be several generations during the year but generally there are two peal periods of activity- the first during February to April and the second during June to August. The nymphs prefer damp and shady places particularly during the midday.

As regards control, use of any strong contact poison can be recommended but in choosing a suitable insecticide it should be kept in view that sometimes the use of an insecticide may lead to increased trouble due to mite pests. Hence, a little experience of the local situation is necessary. Also, systemic insecticides can be quite successful in controlling the pest but they cannot be recommended unless the questions of toxic residues of systemic insecticides inside the fruits of the treated trees is satisfactorily investigated and solved.

2. Mango Mealy-Bug (Drosicha Mangiferae):

The large fleshy flat- bodied creatures with a length of up to about a centimeter and half and breadth of a little less than a centimeter, covered with ashy-white mealy powder and crawling up or down tree- trunks or on the ground round the tree-base or even invading the houses if the mango trees are near about.

These are the mango mealy-­bugs and because of their large size, they are also referred to as the giant mealy- bugs; they are too prominent not to attract attention even when they are small in number and they create a rather alarming nuisance when they are in large numbers, necessitation an s.o.s to those who are likely to know about such matters. These are insects belonging to the bug group.

Thus, their common name is self- explanatory. Like most bugs they suck the plant- sap and although their name seems to suggest that they are specific pests of mango only their list of food plants includes at least 62 species of trees, shrubs and herbs, like mango, guava, peaches, plump, rose, castor, etc. Their sucking activity, when they are in large number, devitalizes the plant and they produce honeydew, which encourages growth of a sooty mould, giving a very unhealthy look to the plant as a whole. At times, they are found clustering in masses on young shoots like fungus outgrowths.

The scientific name of the most common species of this pest is Drosicha mangiferae and it has been reported from many places in India and China. There is a well- established sexual dimorphism in the adult stage which is generally found during the midsummer period, i.e., from April to June.

The description given above applies to adult females, which are wingless and large- bodied. The male, on the other hand, is a winged creature with only one pair of wings and very delicate reddish body which flies actively and fertilizes the females. The male adults have also much shorter longevity than the female adults, which live for about a month.

The adult gravid females after fertilization crawl down along the tree- trunk to the ground where they lay eggs at depth of about 5 to 15cm and in clusters of 300 to 400 eggs each. The oviposition is generally confined to an area near and around the base of the tree. There activities of migration from the tree downwards to the ground and oviposition in the soil are generally confined to the months of April, May and June. The males die soon after mating and the females soon after oviposition.

The eggs laid in the soil take quite a few months before they hatch and their hatching has been reported to be quite appreciably influenced by the temperature and moisture conditions of the soil. The result is that hatching can be as early as November of the same year or as late as March of the succeeding year. Late monsoons and winter rains have been reported to delay hatching.

The young nymphs soon after hatching crawl about in search of some suitable food- plant on which, if found, they spend some time. Thereafter, they begin their ascent along the tree- trunks and this upward migration lasts for several weeks. On reaching the fresh growths, the nymphs congregate there and begin to suck the plant- sap. They moult thrice during their nymphal period which lasts about three months or more, depending on the environmental temperature.

Thereafter, the nymphs developing into males undergo some sort of pupation and transform themselves into winged adults and the female-producing nymphs do not undergo any appreciable change except in size. Thus, there is only one generation during the year. Unlike many other coccids, the nymphs of this pest do not remain stationary although they are sluggish.

From the foregoing account it will be seen that the rationale of the control of this pest is somewhat on the following lines:

(a) Raking of the soil around the base of the tree which has been infested, so that the egg- masses get exposed to the sun and heat and get killed. Also, the application of a soil insecticide in the same area when hatching begins or is expected, so that the just hatched nymphs may be poisoned.

(b) Application of a sticky band round the tree- trunk so as to check the nymphs from crawling up the trees. Many kinds of sticky bands have been recommended. Incorporation of insecticide in the sticky band is likely to increase the effectiveness of this band. Even making a fairly wide insecticidal barrier round the trunk can lead to effective poisoning of the nymphs. In recent years it has been found that banding the tree trunk with 300 mm wide alkathene sheet of 400 gauge prevents the ascent of mealy- bugs.

(c) Strong organ-phosphorus over insecticidal sprays which can penetrate the waxy covering over the nymphal body can control the pest but such applications are likely to be more effective if carried out when the nymphs are young, and the concentration of the sprays has to be considerably increased if they are too be applied when the pest is in the advanced stages of its development.

3. Mango Stone Weevil (Sternochetus Mangiferae):

The mango stone weevil quite a peculiar pest which not only causes annoyance and aversion in mango- lovers but also mystifies them. In areas in which this pest is prevalent, it at times so happens that when one is about to eat a mango fruit which is apparently quite healthy, on is bewildered to find a fairly large- sized adult weevil emerging out of it and flying away.

This creates aversion to eating the fruit because of the obviously unhygienic content of the apparently healthy fruit and bewilderment because unless one has learnt about its full life history one is not able to understand the apparent magic as to how the beetle got into the fruit when there was no external sign of any kind of entry- hole on the mango fruit.

The adult weevil is about 8 mm. in length and about 4 mm. in breadth, greyish brown in colour and with such a pattern as to make the weevil indistinct from the ground background of the bark of the mango tree. In the non- fruiting season, this beetle remains practically in hiding under the bark and in other niches.

It can stay like this for months. Some say it feeds on the mango leaf in some seasons and others have observed that it can live without food and water for months. It feigns death when disturbed. Its activities are generally nocturnal. However, when the fruiting season begins and the mango fruits are still quite tender, this beetle lays eggs on the surface of the mango fruit.

The process of egg- laying is also quite peculiar. The mother- weevil surveys the surface of the fruit as if trying to spot out with the help of its snout and antennae a suitable place for egg- laying. Thereafter, it carves out with its mouth- parts a boat-shaped depression which is so shallow what even liquid does not ooze out from it.

Thereafter, the insect turns round and further assesses the suitability of the scooped out place and then lays there a single egg, which it covers with a small quantity of transparent liquid secretion. It then turns round once more and makes, now with the help of its mouth, a crescent- shaped cut near the posterior end of the egg. This cut, unlike the shallow depression scooped out earlier, is so deep that there is quite a copious flow of liquid from it and liquid also covers the egg completely and dries up into a kind of resinous protective cover for the egg.

This process of egg- laying is so precise and methodical that it takes on an average 15 minutes to lay one egg and one weevil lays up to about 15 egg in a day and about 300 during a period of three months. There are several mattings during the life- time of one weevil and egg- laying and mating at times alternate. Up to three- dozen eggs can be found in a single fruit.

These eggs hatch within a week or so and the just- hatched larva is exceptionally cylindrical in shape for a weevil larva. It immediately begins to burrow into the mesocarp flesh of tender fruit and soon reaches the region where the endocarp seed coat is still very soft. Once the larva crosses this barrier of the seed coat, which is yet in the making, it reaches the region of the seed endosperm where it can spend the rest of it’s in an environment of plenty and safety.

If, however, the seed coat has hardened before the larva has bored it, then that larva has very little chance of survival. This fact seems to set a limit to the age of the fruit up to which successful infestation is possible. Inside the seed endosperm the larva feeds, grows, moults five times during a period of about five weeks, pupates for about seven days and finally transforms itself into the adult weevil.

In the meantime, however, all the injury that was done to the mango skin, flesh and seed coat gets so nicely healed up that the mango fruit appears to be absolutely healthy with developed insects inside its stone and the number of these insects in a single stone may at times be as large as half a dozen. During this period if the infested fruits fall and its fleshy portion decays, then the adult cuts out an exit hole and emerges directly from the stone.

If however, the fruit has not fallen, then the adult has to cut through the mango pulp to come out and create the abhorring scene of the large insect emerging out of a nice healthy-looking mango fruit which the mango- lover is about to knife for eating.

As regards other interesting facts about the life- history of this pest, special mention may be made of the extraordinary longevity of the adult stage. It can live up to about 21 months. Even under unfavourable conditions, it can live for several months. It is also noteworthy that so far as is known, the pest is monophagous and attacks only mongo.

Another interesting feature of this pest is that it seems to be very sensitive both to temperate and to low humidity, so much so that in India it is confined mostly to humid areas in the southern and coastal regions. The same appears to be applicable to its world distribution because it inhabits all the mango regions bordering the Indian Ocean. It has not yet reached North, South and Central America. It is said to be a native of South- East Asia. The nature of the damage is obvious from the foregoing account. As regards the extent of loss, sometimes even 100 percent of the fruits are infested.

All the same, under certain conditions the damage is mostly to the seed. For example, if the mango is consumed before the adult is ready to cut its way out, then practically no damage will be noticed. In such cases the main economic loss is left by those who deal in raising root stocks because the viability of the seed is bound to be very adversely affected.

Also, a very great handicap is experienced in trying to develop the export market for mangoes. For example, the mainland of the U.S.A. does not allow mango imports from India mainly because of the apprehension that this pest may get introduced into that country. Under these conditions the control problem for this pest has two distinct facets: one is to reduce infestation below the economic level. For this purpose that best course is to kill the adults just before the fruiting season by thoroughly treating the bark where they hide.

The second facet is to treat the infested mango with a view to killing the insect stage inside the stone by such means as will no harm the fruit in any away. It has been an unsolved problem in the world till very recently when we in India have been able to develop a hot water treatment, which kills the insects’ stages inside the stone without causing any harm to the fruit itself.

Surprisingly, it has been discovered that this insect inside the seed stone gets killed by dipping the fruit in hot water at 50° + 0.5°C for two hours, although the fruit fly larvae living in the pulp region, i.e., much near the surface, are not satisfactorily controlled. However, it is also possible to kill the fruit fly larvae present in the pulp by incorporating in the hot water a little ethylene di-bromide (14.47 ppm). The bromide residues in the pulp, after 72 hours of such a treatment, have been found to be less than 1.5 ppm, which is much below the tolerance level of 10 ppm.