pests of lepidopteran

A detailed description of some of the major damage causing pests of lepidoptera

1. Lepidopteran pests

2. Lepidoptera The Lepidoptera  is an order of insects that includes moths and butterflies (both are called  lepidopterans ).  Lepidopteran species are characterized by more than three derived features, some of the most apparent being the scales covering their bodies and wings, and a proboscis.

3. butterflies and moths are holometabolous, meaning they undergo complete metamorphosis.  The larvae are commonly called caterpillars, and are completely different from their adult moth or butterfly forms, having a cylindrical body with a well-developed head, mandible mouth parts, three pairs of thoracic legs and from none up to five pairs of prolegs. As they grow, these larvae change in appearance, going through a series of stages called instars. Once fully matured, the larva develops into a pupa.

4. Pectinophora gossypiella   (Saunders) The Pink Bollworm It is a serious pest of cotton  

5. Adult is a small moth having wingspan of 10-15 mm, dark brown, with irregular black markings on the fore wing. Hind wing silvery gray with no distinct markings.

6. Fecundity is about 150 eggs/female. Eggs are flattened, pale yellow with striated surface and laid in the night on bracts, buds or flowers, singly or in small groups. Incubation period is 4-6 days. Larvae are pinkish in color with brownish head and 10 mm when full grown.  Then it penetrates the lint until it reaches the seed, which also it bores and damages.

7. There are four larval instars and total larval development takes 20-30 days depending on temperature. Larvae overwinter by curling inside cotton seeds and become active again in April. Pupation takes place either in the lint or in debris or under bracts or bark on the plant.  Pupal period is 7-10 days and total life cycle is completed in 4-5 weeks

8. Cultural control: Threshing and thoroughly burying all plant remains after cotton. killing the larvae within seeds or lint bales by heating to about 60ºC. Mass trapping with long-lived pheromone traps.

9. Chemical control: Organophosphates were used in the past to control the pest Genetically modified cotton: The use of modified Bt cotton, which expresses toxins from  Bacillus thuringiensis  (Bt), has reduced the need for pesticides.  

10. Tryporyza   incertulas The Yellow Stem borer

11. This is primarily a pest of rice but also has been recorded to feed on maize and some wild grasses.

12. Adults show sexual dimorphism . Eggs are oval, flattened and whitish in colour . Incubation period of eggs is 5-8 days. Larvae are pale yellow in colour with a brownish head, 20 mm long and bore into the stem near the node. They usually feed on the lower part of the stem and migrate from one plant to another to mature. There are 6 larval instars and larval development takes 20-27 days.

13. Pupation takes place inside a whitish silken cocoon within the rice stem, near the root-stem joint. Before pupation larva cuts an exit hole on the stem, above the surface of water and covers it with a silken web as an exit for emerge. Pupal period is 9-10 days or longer in cold weather. Total life cycle takes about 45 days.

14. Damage The larva feeds inside the stem and makes gallery causing dead heart in younger plants. The flowering plants show white head.

15. Control Collection and destruction of egg masses and plants showing dead hearts helps to reduce pest population, particularly in nurseries. Burning of stubbles or ploughing the field after harvesting is a good cultural practice . Early or late planting is recommended in areas of heavy infestation.

16. The following natural enemies keep the pest population under check : Egg Parasites:  Trichogramma sp.    Larval parasites:  Amauromorpha accepta schoenobii ; Isotima javensis .  Larval- pupal parasite:  Trichomma sp.

17. Cnaphalocrocis medinalis Rice leafroller The larvae are considered a pest on  Oryza sativa   and others.

18. The moth is very active, bright yellow or straw in colour with two distinct wavy lines in the fore wing and one wavy distinct line in the hind wing.

19. Eggs are laid singly or in groups arranged in longitudinal rows on the undersurface of the leaves which are scaly white in color . Incubation period is 4–8 days. 5–6 larval instars are found, larval period is about 22–23 days. It pupates with in the infested leaf fold for a period of 6–7 days. The fully grown caterpillar is green in color and is 16.5mm long. The total life cycle completed in about 5 weeks.

20. Once protected in leaf roll , the larvae scrape and feed on the green tissues (the mesophyll layer) of the rice leaves, resulting in the appearance of linear, pale-white stripe damage.

21. Control Host-Plant Resistance Several rice lines transformed with toxin genes from Bacillus thuringiensis (Bt) have been shown to be highly resistant to C. medinalis . Cultural Control Wider spacing and low usage of nitrogenous fertilizer decrease the percentage of leaf folder infestation. Early planting may enable plants to escape a high degree of defoliation . Chemical Control  Many different kinds of insecticides including neem seed oil ( Saxena et al., 1980) have been used for leaffolder control

22. Biological Control C . medinalis has a rich community of natural enemies in insecticide-free ricefields . In China, Trichogramma japonicum and Apanteles cypris are the most important egg and early larval instar parasitoids. In Sri Lanka, larval parasitization ranges from 38 to 70%. Five parasitoids (four hymenopterans and a tachinid ) are quite common.

23. Rice Caseworm ( Nymphula Depunctalis ) It is found in all the rice growing tracts of India and assumes serious proportions in certain season under swampy conditions.

24. Tiny eggs are laid on leaves and leave sheath in rows and batches. Under South Indian conditions a female lays about 150 eggs which hatch in about a week.

25. Young larvae feed by scrapping the leave surface. The larva makes a cylindrical, tubular case out of a portion of the leaf cut and remains inside it, moving with the case on the leaves. It feeds on the leaves actively and becomes fully grown in about 20 days reaching a length of 10-12 mm. 

26. The larval stage pupates inside the last case. Before pupation the case is attached to the leaf sheath above the water level and its both ends are plugged. The pupal period lasts for about a week, after which it is converted into an adult insect. The pest is active during the monsoon and there may be two or three broods in a season . The life cycle is completed in about 35-40 days.

27. The caterpillars can breathe in aquatic medium with the help of branched tubular gills, hence the pest infestation is found in the fields which are filled with water. Dispersal of larvae takes place by floating on water. The case with larva drops in the water and it paddles to reach another plant.

28. Control Cultural Method: 1. Draining out the stagnant water from the field is very much effective in reducing the population of this pest. 2. Rotation of crop is advisable. 3. Destruction of weeds around the paddy fields (weeds acts as alternate host of this pest). Chemical Method : 1. Spraying with DDT or dusting the crop with 10% BHC or Carbaryl at the rate of 15-20 lbs/ acre is effective. 2 Spraying of “К-oil” or any other insecticides on the water surface kill the caterpillars.

29. Biological Method: 1. Introduction of Elasmus sps ; Apalteles sps ; Bracon sps ; Hormius sps is effective in controlling the destruction caused by the larvae because they paracitises the larval stages. 2. Introduction of Pediobius sps and Apsilops sps is effective in controlling this pest because they parasitises the pupal stage.

30. Snails are useful predators of eggs of the rice caseworm. The larvae are fed upon by the hydrophilid and dytiscid water beetles. Spiders, dragonflies, and birds eat the adults.

31. Rice Swarming Caterpillar ( Spodoptera mauritia ) The adult is stoutly build dark-brown moth with a Bloch of white on the fore wing. The males are characterised by immense tuft of hairs on the fore legs.

32. The female moth is nocturnal in habit and mate just 24 hours after their emergence. The eggs are laid in batches on various kinds of wild grasses and paddy leaves . The number of eggs laid per batch may be 200-300 .

33. The fully grown larva is smooth, cylindrical and has a large pale colour with sub-dorsal and dorsal stripes. The larvae feeds on rice leaves undergoes six instars and grows to a length of 3.8 cms . It feeds during night and hides in soil in day time. Pupation takes place in soil in an earthen cocoon.

34. Plants attacked by caterpillars have skeletonized leaves, shot holes, and dieback stems. Commonly the entire paddy crop dies within few days due to swarming attack. 

35. The caterpillar feed at night on the leaves and defoliates the plants completely. Generally they invade the transplanted plots in large number in big swarm and devastate the whole plot overnight like cattle’s do. After finishing the crop of one field the swarm marches to another field in a regular army formation manner, hence this pest is also called as “Army worm”.

36. Control Cultural Method: 1. In case of severe attack of this pest, the entire area should be isolated by trenching and the crop should be ploughed up . Chemical Method: 1. The field edges and bundh should be dusted with Gammexine (0.025 %) at the rate of 15 lbs/acre in early stages. 2. Application of contact insecticide like BHC, Carbaryl or Methyl Parathione controls the caterpillars effectively .

37. Mechanical Method: 1. Collection of caterpillars with a hand net or sweeping basket and their destruction. Biological Method: 1. In the seedling stage, the nurseries may be flooded with water. This will bring up the caterpillars to the surface from where they will be picked up by predator birds. 2. In small areas duck can be released in the field which feed upon the larvae of this pest.

38.  Adults can eliminated by introducing Bolas spiders to the fields. This spider has the ability to spray a pheromone similar to female moth, to attract male moths. Moths traps like wing traps and unitraps can also used to collect adults .