DIVERSITY OF INSECTS IN THE MULBERRY ECOSYSTEM

A.Mahima Santhi and S. Prasanna Kumar

In this issue we present a very interesting paper by two entomologists of South India. The paper deserves special attention primarily because of its ecological approach to sericulture and entomological perspective to pest insects. Even though the primary responsibility of an agricultural entomologist is to device means to eliminate insects designated crop pests and to protect those designated economically important; the ecological balance between the pest, other (neutral) insects and the crop environment deserve his/ her attention in a long term perspective. This paper is notable at a time when such studies (at least in Moriculture) are becoming increasingly rare.

Dr. A. Mahima Santhi is a scientist with Central Silk Board, India. A post graduate in Agriculture from Tamil Nadu Agricultural University (TNAU), she earned her PhD in Agricultural Entomology from Manonmaniyum Sundaranar University, Thirunelveli, India. She holds more than eighteen years of research experience in sericulture and entomology under CSB. Currently she is heading the technical wing of Kerala State Sericulture Cooperative Federation (SERIFED) as its Deputy Director.

Dr. S. Prasanna Kumar is Professor & Head, Department of Zoology and Dean of Sciences, Scott Christian College, Nagercoil, India. A PhD in Zoology, he has more than thirty years of research and teaching experience in Entomology.

INTRODUCTION

The perennial nature of mulberry combined with monocultural practices, harbours several pests throughout the year with seasonal variations (Rangaswamy et al., 1976). The production of appreciable quantity of quality mulberry leaf is often hampered by insect pests belonging to large number of insect orders. Apart from insect pests, predators, parasitoids, naturals and detrivores also survive on mulberry plant. Studies on diversity are the preliminary for any management work. . Narendran (2001) explained that taxonomy is the foundation of biodiversity. Hence a survey was conducted in mulberry ecosystem to survey the diversity of the insects. The taxonomic diversity of the insect communities was worked out in the mulberry ecosystem.

MATERIALS AND METHODS

Survey on the insect diversity was conducted at Nagercoil, South India for continuous two years. The details of materials and methods are described here.

Insect assessment

The mulberry garden was divided into five sub plots, four at corner, and one at the centre. From each sub plots ten plants were selected at random for the observations. Thus 50 plants were observed every fortnight for two years. The number of mealy bugs, grasshoppers, scales, whiteflies, thrips, leafhoppers, bugs etc., feeding on the plants were counted. The total number of predators and parasitoids present on each selected plant were counted. Ants attending mealy bug populations were also recorded. Other insects such as butterflies, cockroaches present on the plant at the time of observation were also recorded. The soil insects such as carabids, termites were counted around the selected plants using Berlese funnel method. The average of the counted insects per ten plants was treated as one sample. The insects were collected, observed and unknown insects were preserved for identification according to Schauff (2002). The insects of various orders of class Insecta were distinguished.

RESULTS

The insects collected were identified and grouped in different orders of class Insecta according to Ambrose (2004). An average of 3388 insects was recorded per sample. Insects belonging to ten orders were recorded. The order Hemiptera recorded 60.86 per cent of total insects and order Hymenoptera recorded 22.05 per cent of insects. The order Coleoptera recorded 8.65 per cent. Other orders such as Isoptera, Lepidoptera, Dictyoptera, Odonata, Orthoptera and Thysanoptera accounted the rest. The distribution is detailed in chart.1

The details of insects recorded were given below as orderwise

Order: Hemiptera

It was the largest hemimetabolous orders with piercing and sucking mouthparts, with two sub orders, Homoptera and Heteroptera. Insects from both suborders were observed in the field.

Suborder: Homoptera

Insects which do not possess scutellum and has uniform leathery forewings are homopterans. Insects observed from this orders were herbivores. Important ones are detailed below.

Family: Pseudococcidae

Pseudococcids, generally called mealy bugs were the dominant insects. Their body was covered by mealy coating. Eggs were laid in loose cottony sac. Young ones were gregarious. Female were wingless and males winged. These mealy bugs secreted honey dew hence attended by ants. These ants protected mealy bugs from natural enemies. In the present study three species of mealy bugs were observed in the field. The mealy bugs recorded were.

a. Maconellicoccus hirsutus

These mealy bugs were present throughout the year except rainy months followed by winter season. The population was low during rainy season. The mealy bugs prefered tender leaves and twigs. Continuous feeding by mealybugs caused severe tukra symptoms.

b. Ferrisia virgata

The tailed mealy bug, which is a polyphagous pest, also infested young mulberry leaves. Their occurrence was very meagre to show any visible symptom, in few cases young shoots tips dried due to continuous feeding.

c. Planococcus citri

This was a serious pest found almost in all the months in the second year and summer months in the first year. Young ones fed on tender leaves and caused curling of leaves but not clustered like tukra. The grown up ones were seen feeding on the nodes and uniformly distributed throughout the stem. On continuous feeding the leaves become yellow and withered off. When there was severe feeding the terminal bud was killed which caused the sprouting of ancillary bud. Severe damage made the stem to dry. The mealy bugs were attended by black ant, Camponotus compressus.

d. Paracoccus marginatus

Recently papaya mealy bug incidence was noticed on mulberry crop in western parts of Tamil Nadu and Palghat district of Kerala. The papaya mealy bug is found on leaves, stem and twigs. Adult females are yellowish with short waxy filaments around the margin. The dispersal stage is the first instar crawler. The mealy bug injects a toxin as it feeds on leaves, which results in chlorosis (yellowing), stunting, deformation, early leaf drop, and buildup of honeydew. Sooty mould growing on honeydew excreted by the mealy bugs interferes with photosynthesis. Heavy mealy bug infestation kills the plants.

Highly polyphagous in nature.

Family: Margarodidae

The insect Icerya aegyptiaca was seen feeding from undersurface of the leaves. These insects were seen in groups or single. These bugs were bigger in size and orange coloured with black legs. The body was covered with white mealy waxy strands. Eventhough the pest was seen in majority of the months, the damage symptom was not serious. The population was higher during summer months.

Family: Aleyrodidae

Aleurodicus dispersus, the white fly were minute active whitish insects resembling tiny moths. The body and wings were covered with white powdery coating. The eggs were laid in irregular spirals. The white nymphs and adults were seen on lower surface of leaves. The desapping of leaves depleted the nutritive value of leaves. The incidence was noted from late January to early April.

Family: Membracidae

The cow bugs Oxyrachis tarandus were seen feeding on tender shoots. The nymphs were attended by ants. Their occurrence was very meagre. Small specks were seen at the feeding site.

Family: Coccidae

The black scales, Saissetia nigra were seen on stem and on lower side of the leaves. The occurrence was noted from January month to May. No severe damage noticed.

Family: Cicadellidae

The leaf hopper, Empoasca flavescens, adults, and nymphs fed on tender leaves and caused “hopper burn” symptoms. They were very active and jump, can move sideways. The incidence was noted during July to October months. The insect population was very low to cause economic injury.

Suborder Heteroptera

Family: Pentatomidae

The shield bug, Scutellera nobilis was seen very rarely on mulberry and did not cause much damage.

Family: Reduviidae

The assassin bug, Eirantha armipes were seen during rainy months June-July. This was an effective predator.

Order: Hymenoptera

Family: Formicidae

Beneficial interaction existed between the mealy bug and ants. The dominant M. hirsutus population was heavily influenced by ant population. The predator population in the ant attended colonies was significantly lower. Ants were seen attending mealy bug colonies.

Family: Sphecidae

The mud dauber wasp, Ammophila procera were seen very rarely on mulberry leaves. The females hunt for arthropod prey which serves as food for their offspring.

Family: Encyrtidae

The small parasitoid, Leptomastix dactylopii was rarely seen in the garden. But the parasitized mummies of mealy bug were seen during non-rainy months.

Order: Coleoptera

Coleopterans are the insects with biting and chewing mouth parts with hard exoskeleton. Forewings were hardy and hind wing membranous.

Family: Cerambycidae

The stem girdler, Sthenias gristator was seen during February month of the first year. The adult beetle girdled the young green branches of the mulberry plant and caused drying of the twig. The bark and wood up to the centre were cut by powerful mandibles and in few plants entire twig was cut into two bits.

Family: Curculionidae

Ash weevil, Myllocerus discolor and M. viridanus were seen on mulberry leaves. The presence of this beetle was recorded throughout the year. Their occurrence was slightly higher during summer months. Damage symptoms were not severe.

Family: Scarabaeidae

The dung beetles or dung rollers, Scarabaeus sp were seen on the soil during summer months. They produced dung balls for egg laying. They are grouped under scavengers.

Family: Carabidae

The ground beetle Carabus nemoralis were found throughout the year in the soil. The beetles were mainly predators.

Family: Coccinellidae

Two predatory beetles were recorded. Nephus regularis (Sic.) was the common predominant predator seen feeding on mealy bugs. They were seen inside the tukra curls. The grubs were black coloured with white mealy coating seen inside the tukra curls feeding on mealy bugs. Adults were very small oval shaped brown coloured beetles. The population of this beetle increased with increase in mealy bug population. The activity of beetles was not seen on tukra affected branches with ants.

Another yellow lady bird beetle recorded was Illeis cincta. The yellow coloured grubs and adults were seen on plants feeding on powdery mildew growth on leaves. Their occurrence was higher during winter months.

Order: Thysanoptera

Small insect with rasping and sucking mouth parts.

Family: Thripidae

The thrips, Pseudodentrothrips mori injured the epidermal tissues of leaves and desapped Leaves showed streaks in the early stages and blotches in the later stages. Leaves became brittle and were unsuitable for feeding silkworms. In severe case of attack leaves whither and dried. The attack was seen during May and June of the first year. The second attack was during December to February. Then the attack was repeated during May and June in the second year.

Order: Orthoptera

Medium sized insects with mandibulate mouthparts, the hindlegs are enlarged facilitating jumping.

Family: Acrididae

The short horned grasshopper Neoorthacris nilgriensis or wingless grasshopper was present throughout the year. The population showed slight increase during summer months when other plants dried without irrigation. The insect had shorter antennae and ovipositor. The wings were not present.

Other insects of this order, long horned grasshopper, Tettigonia viridisima of Tettigonidae and field cricket, Gryllus sp. of Gryllidae were also present in the garden.

Order: Isoptera

Soft bodied, social and polymorphic winged species living in large colonies, with biting mouth parts.

Family: Termitidae

The termites Odontotermes sp. feed upon roots and barks of young and old plants. Severe attack leads to death of plant. These termites build colony structure and live socially with workers, soldiers and queen. The presence of termite was higher during summer months.

Order: Lepidoptera

Lepidopterans are holometabolous insects, adults brightly coloured, winged insect with long tubular suctorial mouthparts. The larvae are soft bodied caterpillars with biting mouth parts. The pupae are generally enclosed in a cocoon.

Family: Pyraustidae

Diaphania pulverulentalis, the leaf roller of mulberry, incidence were recorded during September and October months. The larvae damaged by folding the leaves and by webbing the tender shoots. Early instars fed from inside the web and skeletonize the leaves. Later instars fed the tender leaves voraciously. Larval feeding caused qualitative and quantitative loss of leaves.

Other insects of Lepidoptera present were Eurema hecabe of Pieridae, Catochrysops cnejus of Lycaenidae and Danaus plexippus of Danaidae. They were neither harmful nor useful to mulberry.

Order: Odonata

The dragonfly, Libellula quadrimaculata of Libellulidae and Damselfly, Protoneura sp of family Protoneuridae were commonly seen in the mulberry leaves. These insects were general predators.

Order: Dictyoptera

Suborder: Mantodea

The preying mantis, Mantis religiosa of family Mantidae was recorded. They were effective general predators.

Suborder: Blattaria

The field cockroach Blattella sp of family Blattellidae were seen scavenging on mulberry plants. The insects occupied the tukra curls for shelter.

DISCUSSION

The order Hemiptera was the prominent order. Around 60 to 62 per cent of insects belonged to order Hemiptera. Under Hemiptera order, six homopterans and two heteropterans were recorded. The family Pseudococcidae with four species of mealy bug was the largest family recorded. Next homopteran recorded in the garden was whitefly. Hymenoptera was the second dominant order in the garden. Ants were found in association with the homopterans. There was a beneficial interaction between homopterans and ants. The parasitoid of mealy bug Leptomastix dactylopii was also recorded under this order. These insects were used in bio control programmes often in mealy bugs. (Noyes and Hayat, 1988).
The order Coleoptera was the third largest order in the garden. The coccinelids were dominant and seen throughout the year. They were effective predators of soft bodied insects and also feed on fungal growth such as powdery mildew. This was also reported by Joshi et al., (2003). The carabids were found next to coccinellids in the field. Allen (1979) reported carabids as beneficial insects.

Insects of Isoptera, Lepidoptera, Dictyoptera, Odonata, Orthoptera and Thysanoptera were found in mulberry ecosystem. Among these insect orders, Odontotermes obesus of Isoptera, Diaphania pulverulentalis of Lepidoptera and Pseudodentrothrips mori of Thysanoptera were serious pests of mulberry ( Sathya prasad et al., 2000 and Dandin et al., 2001).

The trophic interaction between plants, herbivores, natural enemies and others were studied in the mulberry field and detailed in chart.2. In the present study 68 per cent of phytophagous, 4 per cent of predators, 25 per cent of ants, 1.5 per cent of scavengers, and 1.5 per cent of neutrals were recorded. These studies should be done in all mulberry ecosystems. The natural enemies should be preserved in the garden. The balance between phytophagous insects, natural enemies, detrivores, and neutrals should be maintained for a successful mulberry crop.

REFERENCES

  Allen, R.T. 1979. The occurrence and importance of ground beetles in agricultural and surrounding habitats. In T.L. Erwin, G. E. Ball and D.R white head (eds) Carabid beetles their evolution, natural history, and classification. W.junt, The Hague, The Netherlands. 485-505pp
  Ambrose, D.P. 2004. The insects, structure, function, and Biodiversity. Kalyani publishers, Chennai. 821 p.
  Dandin, S.B., Jayaswal, J. and Giridhar, K. 2001. Hand book of Sericulture technologies. Central silk board, Bangalore, 287p.
  Joshi, S., Mohanraj, P., Rabindra, R.J. and Rao, N.S. 2003. Production and use of coccinellid predators. Project Directorate of Biological control, Bangalore, India Bull. 32, 26 p.
  Narendran, T.C. 2001. Taxonomic Entomology, Research and Education in India. Curr. Sci., 81 (5): 445-447.
  Noyes, J.S and Hayat, M. 1998. Oriental mealy bug parasitoids of the Anagyrini (Hymenoptera: Encyrtidae). CAB International, 551p.
  Rangaswamy, G., Narasimhanna, M.N., Kasiviswanathan, K., Sastry, C.R. and Jolly, M.S. 1976. Sericultural Manual, Mulberry cultivation, FAO., Rome,150p.
  Sathyaprasad, K., Manjunath, D., Mala V. Rajan and Sarkar, A. 2000. Screening of mulberry germplasm for tolerance to sucking pests. Abs. Ntnl. con. Str. for Seri. Res. dev. CSR&TI, Mysore, M 1 :7
  Schauff, (2000). Collecting and preserving insects and mites, techniques & Tools, Systematic Entomology laboratory, USDA, Washington. 66p.

Is Perfect Research Possible?

GK. Rajesh
Recently I was asked to write an essay, expressing my views on the statement "There Is No Hope of Doing Perfect Research" by the selection panel of a content writing employer. I gave them the following answer, which I wish to share with my readers.

   The given question on research can be put to any ‘human activity’ and still be found equally difficult to answer. Is it possible to do anything perfect? The quickest possible response is ‘no’. A little reflection will show that this answer in the negative has nothing to do with the activity under question. It is the perceived notion of the word ‘perfect’ that drives the respondent towards the negative answer because anything perfect is understood to be ‘nearly impossible’ let alone research. Usually ‘perfect’ as an adjective is used for harmless, jocular exaggeration of the quality under question. For example the expressions ‘a perfect fool’ or ‘perfect nonsense’ do not mean the qualities under question to be absolute. They are rather cursory and superficial remarks than conclusions of any serious investigation. One rarely encounters such expressions in scientific literature. Similarly the expression “perfect research” is not found in any standard literature. Instead, terms such as reliability, validity, credibility transferability and trustworthiness are used to indicate various desirable qualities of research work (Golafshani 600). Hence, in this essay the term ‘perfect’ will be used to collectively represent these terms.

   The term ‘research’ is defined as follows: “Scientific or scholarly investigations especially study or experiment aimed at the discovery, interpretation or application of facts, theories, or laws” (Allen1188), “Careful study or investigation, especially in order to discover new facts or information” (Hornby 996), “Diligent, protracted investigation” (“Webster’s” 1071). Thus research constitutes investigation and discovery/ interpretation/application of knowledge. A research may be safely regarded as fruitful if it results in the discovery of an object or a procedure which it is intended for. To call it perfect demands more assessment with regard to the quality of the discovery (whether it has all the qualities, excellences or elements that are requisite to its nature or kind), the procedure adopted (whether without fault or defect) and the way in which it was executed (whether economic and without negative externalities). For example the discovery of penicillin, in spite of its great utility may not be called perfect research since it was rather an accidental finding than result of systematic investigation originally intending to its discovery. Alexander Fleming wrote “… I certainly didn’t plan to revolutionize all medicine by discovering the world’s first antibiotic, or bacteria killer, but I suppose that was exactly what I did …” (qtd. In Wikipedia.org). The discovery of molecular structure of DNA traced from its origins in 1868 by Friedrich Miescher to the celebrated work of Watson, Crick and Wilkins in 1962 could be considered as a continuum of perfect research. While quantitative research1 is more amenable to such assessment, qualitative research2 is not.

   Two case studies on my own research cited here are examples of quantitative research with mixed results. The first was my Master’s Degree dissertation work on temperature induced protein synthesis in silkworms (Rajesh GK, “Induction of Heat Shock”). Heat shock proteins are specialized proteins which are synthesized in living cells under stress of any kind. They are known to perform protective actions within the cell under trauma. My intention was to study the threshold temperature which triggers heat shock response in silkworms. The theoretical premise in which the experiment was set was excellent and the research question meaningful. But the work lacked in focus. In my slightly over enthusiastic mindset I set a very ambitious objective, not only to track down heat shock proteins but also to assess their differential expression in two breeds of silkworms. The experiment proved to be too big to fit in the time span permitted for an MSc dissertation. Though I could complete the experimental part as per my original design and with a high level of accuracy3 I could not subject the huge data generated into fruitful analysis and interpretation. Nevertheless the fraction of data that I could use was systematically put together into a neat report which received good remarks. I realized my mistake only at the end of the work. I had ben simply over ambitious and neglected the importance of focusing on the specific problem and conceptualizing the research work in a practical manner. I am sure, given more time to understand my mistake, the work could have been more systematically organized and made perfect. After all the empirical investigation was done perfectly, evidenced by the concordance of observations in replications.

   The second example is of my MPhil (Economics) dissertation on factors determining adoption of a (new and improved) technology by sericulture farmers in India (Rajesh GK, “Diffusion”). I investigated the reasons why a superior silkworm hybrid had not diffused well in the country in spite of great efforts from the government for more than a decade. Being better informed and having grown wiser out of the previous experience, I was more vigilant and pragmatic this time. After an exhaustive literature survey and expert consultation a very specific and real world problem was spotted down. The proposal was presented before a distinguished panel and finalized after incorporating suggested modifications. The theoretical background was strong and the study was conceived with clarity. The empirical investigation was planned to the minutest detail and the survey questionnaire perfected after a mock survey. The data was subjected to rigorous statistical analysis and the findings were written down systematically into a comprehensive yet concise report. The dissertation was awarded with an A-plus and I received an almost flattering comment from the external jury (which I consider I am not entitled to). But I do not deem the work perfect. Once the survey was completed I realized that in spite of all my preparatory work the sample selected by me was not quite representative of the country and the sample size too small given the diversity of technology adoption strategies employed by the target population. Since it was a time bound assignment I could not extend my survey to capture the diversity. I am sure that it would make a perfect piece of research if repeated with a bigger and different set of samples.

   My own imperfect researches are not convincing proof to conclude that there is no hope for perfect research. I do not agree to the statement ‘there is no hope for perfect research’; it could be so only if the term ‘perfect’ is taken on its ‘utopian sense’ of ‘ideal’. Then it is as good (or bad) as saying- anything human is imperfect. The European Commission’s Expert Group on Assessment of University Based Research commented

   “There is no single set of indicators capable of capturing the complexity of research and research assessment. There is no such thing as a perfect indicator; all indicators have their own specific strengths and weakness, and assessment exercises have to take this into consideration from the outset … (“European Commission” 12).”

If there is no perfect indicator for research assessment there is no point in looking for perfect research. Research is the life blood of human development; it is relentless quest for truth. When truth itself is subject to change, there is no meaning in idealizing research, which is one of the means for attaining it. According to Schwarts, “… research is immersion in the unknown. We just don’t know what we are doing. We can’t be sure whether we are asking the right question or doing the right experiment until we get the answer or the result …” (1771). He calls this “productive stupidity” and concludes that “The more comfortable we become with being stupid, the deeper we will wade into the unknown and the more likely we are to make big discoveries”. Why waste time, thinking whether stupidity is perfect!

NOTES

1. Patton defines quantitative research as “use of standardized measures so that the varying perspectives and experience of people can be fit into a limited number of pre-determined response categories to which numbers are assigned” (qtd. In Golafshani 598)
2. Strauss and Corbin define qualitative research as “any kind of research that produces findings not arrived at by means of statistical procedures or other means of quantification” (qtd. In Golafshani 600)
3. Accuracy with respect to raising the biological specimens, adhering to the scientific standards and in quantifyication and electrophoretic separation of proteins.
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