INTEGRATED PEST MANAGEMENT OF Plutella ...

INTEGRATED PEST MANAGEMENT OF Plutella xylostella AN IMPORTANT PEST OF CRUCIFERS IN MAURITIUS S Facknath University of Mauritius ABSTRACT The IPM approach is being studied for the control of Plutella xylostella (the diamondback moth DBM), a serious pest of cruciferous crops, and various methods are being investigated at the University of Mauritius (UOM) and the Ministry of Agriculture. At the UOM, methods have so far concentrated on the development of botanical pesticides, cultural practices such as intercropping and use of a trap crop, as well as combinations of botanicals and intercropping. Plutella research at the University has also included use of a bacterial pathogen, namely Bacillus thuringiensis, as well as host-preference studies. In association with the indigenous and introduced biocontrol agents affecting DBM, and the normal practice of using overhead sprinkler irrigation, which is known to have a reducing effect on Plutella populations, the combination of experiments actually represent an IPM strategy, which can serve as a basis for a more structured and comprehensive package for the integrated management of Plutella xylostella in Mauritius.

INTRODUCTION Integrated Pest Management (IPM) is an approach to keeping pest populations below a level causing economic loss, through the judicious and compatible use of two or more of several possible control measures: biological, cultural, biology-based, genetic, physical/mechanical and chemical. IPM projects are being developed throughout the world for the control of serious pests of agricultural, veterinary and medical importance. Selection of the control measures adopted as part of an IPM package is based on many factors : available resources, such as money, manpower, technical knowhow, skills; the agroecosystem; geographical location; socio-economic situations, etc. However, the general trend appears to incorporate three main components: Chemical control using botanical pesticides or selected synthetic pesticides; biological control using parasitoids and cultural control using resistant varieties of crops. Plutella xylostella (L.) (Lepidoptera:Yponomeutidae), commonly known as the Diamond Back Moth (DBM), is one of the most important pests of cruciferous crops throughout the world, and can cause serious economic losses if not checked. In the warm, humid tropics this insect breeds throughout the year, and can have more than ten generations annually. The destructiveness of DBM, coupled with the fact that it has the capacity to develop resistance very rapidly to any control measure used singly, has made this pest the focus of IPM research in many parts of the tropical world. Practically all the available methods and pest control technologies have been tried at some time or another for the management of DBM. In Mauritius, development of pesticide resistance by DBM has progressed rapidly from Lannate (methomyl) to Rogor (dimethoate) to Tamaron (methamidophos) to Decis (deltamethrin) to Selecron (profenofos) to Tokuthion( prothiofos). At present the use of Suntap (cartap hydrochloride), Vertimec (avermectin), Cascade (flufenoxuron) and Selecron (profenofos) is recommended, based on the severity of the pest attack (MANR 1995). Considerable research effort is being devoted to developing an IPM strategy for DBM control. Studies are being conducted at the University of Mauritius and the Ministry of Agriculture involving various approaches (Table 1).

AMAS 1997. Food and Agricultural Research Council, Réduit, Mauritius 103

Integrated pest management of Plutella xylostella, an important pest of crucifers in Mauritius S Facknath

Table 1 Research strategies presently being explored for the control of Plutella xylostella in Mauritius Control Approach Research Strategy At the University of Mauritius Allelochemicals Botanical pesticides Microbial control Pathogens (Bacillus thuringiensis) Cultural control Intercropping and use of trap crops Combinations of above Botanicals and cultural control At the Ministry of Agriculture Chemical control Synthetic pesticides and growth regulators Biological control Parasitoids Microbial control Bacillus thuringiensis Physical control Traps Genetic control F 1 sterility

BOTANICAL PESTICIDES At the University, a large number of local plant groups have been investigated for their pesticidal properties against a range of agricultural pests. Table 2 lists a few of the plant species which exhibited strong pesticidal potential against DBM (Facknath 1997). Their effects were varied : Table 2 Plant species exhibiting pesticidal potential against Plutella xylostella Vernacular name Ayapana Botrys Corrosol L’herbe bouc, goat weed Indian privet Lemon grass Melia, bakain, lila perse Neem Vetiver Vieille fille AF CSI GR

Plant species Ayapana triplinervis Chenopodium spp Annona murricata Ageratum conyzoides Ligustrum robustum Cymbopogon citratus Melia azederach Azadirachta indica Vetivera zizanoides Lantana camara

: antifeedant : chitin synthesis inhibitor : growth regulating activity

Biological Activity AF, GR AF CSI, GR GR IN, GR AF, GR, IN IN, AF, GR, RP AF,IN,GR,RP,OVDT AF, GR AF, GR IN : insecticidal OVDT : oviposition deterrent RP : repellent

Neem, melia,lemon grass, ayapana, lantana, vetiver and botrys affected feeding adversely by making the treated host plant unpalatable to the pest larvae. The larvae, although remaining on the host plant, starved to death within a few days. Goat weed, neem, corrosol, lemon grass, ayapana, vetivera, lantana,indian privet and melia affected the growth and development in different ways, resulting in distorted pupae, pupal death, partial emergence of adults and deformed adults. Melia, lemon grass and indian privet were toxic to the larvae and caused significant mortality. Melia, however, is known to be toxic to higher animals as well, and hence its application in pest control is as yet limited. Corrosol inhibited the synthesis of chitin, an amino-polysaccharide, which together with proteins and lipids, forms the insect cuticle.Lack of chitin causes death of the insect at the time of moulting and metamorphosis. Neem also repelled the adult females from laying eggs, thereby reducing the DBM population in the next generation. Moreover, extracts of neem seed kernels, applied to Plutellainfested cabbage plots had no adverse effects on the development and emergence of the introduced AMAS 1997. Food and Agricultural Research Council, Réduit, Mauritius 104


larval parasitoid of DBM, namely Cotesia plutellae (Hymenoptera : Braconidae). The advantages of botanical pesticides over synthetic chemicals are by now very well-documented and well-known. Most of them are safe to prepare and apply; safe to humans, to non-target organisms, to beneficial insects, and to the environment in general; they leave no residues, hence cause no contamination nor pollution; they are often cheaper and just as effective as the synthetics. In most cases their bioactive compounds are fairly complex groups, thereby making it more difficult for the pest to develop resistance. All the plant species listed in Table 2 are easily available in Mauritius and simple extracts of the same can be prepared by the farmer himself. Commercial formulations of A. indica (neem) are manufactured in India, Canada and the US (Table 3), and are being marketed and used in many parts of the world. Interest in these preparations is gaining ground in Mauritius and it is hoped that soon such botanical formulations will be available on the local market. Table 3 Commercial formulations of neem available on the world market Trade Name of Formulation India USA Azatin EC Margosan -0 Neemix -45

Achook Dimilin Jawan Neem Guard NEEMA-S 1 Neemark NeemAzal Neempest Nimbecidine Nimbicilin Nimbitor Nimin (neem-coated urea) Pra Neem Repelin

Bacillus thuringiensis Bacillus thuringiensis (B.t.) was investigated way back in 1976 at the University of Mauritius, for the control of another lepidopteran pest, Crocidolomia binotalis (Ramgoolam 1976), and recently in 1995 for the control of DBM (Goolaub 1995). Turex, a formulation consisting of the B.t. strain GC 91, derived by conjugation of two distinct B.t. strains showing different spectra of insecticidal properties, was studied in laboratory bioassays as well as in field trials, and was found to provide protection comparable to that of the recommended thiocarbamate insecticide - Suntap (cartap hydrochloride). However, contrary to earlier expectations, there are reports of Plutella having developed resistance to B.t. in certain parts of the world (Tabashnik et al. 1990).

INTERCROPPING AND TRAP CROPS Intercropping is an ancient and traditional agronomic practice which, if utilised correctly, can contribute significantly to reduce pest problems. Several field trials have been conducted using different intercrops such as tomato, garlic, coriander and carrot. The intercrops were grown in alternate rows with cabbage, and their influence on Plutella population was estimated. It was observed that the intercropped plots had significantly lower numbers of Plutella larvae and pupae, and a higher yield of good quality cabbage heads, as compared to the control (pure stand) cabbage plots. Tomato exhibited the greatest deleterious effect on pest populations. The reducing action of tomato plants on Plutella when grown in interrows with cabbage, corroborated the reports by Buranday and Raros (1973), and Sivapragasam et al. (1982). Similarly, garlic in interrows of cabbage also has been AMAS 1997. Food and Agricultural Research Council, Réduit, Mauritius 105


reported to decrease Plutella numbers (Talekar et al. 1986). The confusing olfactory and visual cues received from host and non-host plants, leading to disruption of mating, are believed to be partly responsible for the reduction in larval numbers, while tomato is known to release certain volatile chemicals which have a repellent action on the adults. Mustard was tested for its role as a ‘trap crop’. Alternate rows of mustard and cabbage had lower numbers of Plutella larvae and pupae on the cabbages as compared to those on the pure stand cabbage. Mustard attracts Plutella and other crucifer pests, thereby drawing them away from the main crop. Plutella has been reported as showing a distinct preference for mustard for oviposition. This attractance and oviposition stimulant property of mustard has been attributed to the effect of volatile compounds such as isothiocyanates released by the mustard plants (Srinivasan and Krishna Moorthy 1991). Host preference studies at the University have shown that Plutella prefers cabbage over both cauliflower and broccoli, and cauliflower over broccoli. Apart from lowering infestation, the intercrops can also provide additional revenue to the grower.

COMBINATION OF INTERCROPPING AND USE OF BOTANICALS The effect of intercropping with plants of either tomato, coriander or garlic, combined with the application of neem seed kernel extract was found to be even more efficient in protecting cabbage plants in the field. In fact, the cabbage-tomato-neem combination treatment was observed to be comparable to that of the recommended insecticide, Suntap (cartap hydrochloride), with respect to the number of Plutella larvae and pupae, number of infested cabbage plants per plot, and the quality of harvested heads (Facknath 1996).

IPM The above-described studies were conducted to compare the effects of specific treatments (botanical pesticides, B.t., intercropping, trap crops, botanical pesticides in addition intercropping ) with their respective controls, and with each other. However, it must be remembered that these trials were carried out both in the laboratory and on farm; in the open field the natural enemies such as predators, parasites and pathogens of Plutella xylostella exist; these are the indigenous species as well as those deliberately introduced into Mauritius for the biocontrol of Plutella, for instance the larval parasitoids, Cotesia plutellae and Diadegma semiclausum. Although the role of these natural enemies was not quantified in the above-mentioned studies, they definitely must have contributed to the overall results obtained, in the control of DBM in the experimental plots. Furthermore, in all the field trials, overhead sprinkler irrigation was used, as is the normal practice on the University farm. In case of Plutella, this type of irrigation has been shown to have a significantly negative effect on Plutella populations by causing the eggs and larvae to be dislodged and washed off the plant and to drown. Overhead sprinkler irrigation also disrupts adult flight, mating and oviposition (Nakahara et al. 1986; Talekar et al. 1986). Thus, in the experiments designed to study the combined effects of intercropping and botanical pesticides, in actual fact, the IPM strategy comprised of the application of botanicals, biological control, and cultural practices such as mixed cropping (intercropping or use of trap crops) and overhead sprinkler irrigation. The satisfactory results obtained with this combination suggest that this IPM strategy could be used as a base on which to develop an improved and more comprehensive IPM package through the incorporation of some selected measures. A few species of Plutella egg parasitoids of the genera Trichogramma and Trichogrammatoidea and pupal parasitoids such as Diadromus spp have been reported in the literature, as also other parasitoids such as Brachymeria spp, Eriborus spp and Agathis spp (Waterhouse 1992). A granulosis virus (Wakisaka et al. 1992) and fungal pathogens, for example Paecylomyces spp (Alam 1992), Pandora blunckii and Zoophthora radicans (Riethmacher et al. 1992) have been documented as infecting DBM larvae under conditions of high humidity. Some of these could be tried in Mauritius. Use of resistant varieties, crop rotation, use of trap crops in



appropriate planting patterns could be included as part of the cultural practices, while the use of yellow, sticky traps would be a simple, effective mechanical method.

CONCLUSION Studies conducted at the University of Mauritius and the Ministry of Agriculture indicate that we are more than halfway towards developing the desired IPM strategy for the control of the diamondback moth in Mauritius. A few parasitoids have already been established, among them the one that has been most successful in similar situations in many other countries, namely Cotesia plutellae. B.t. is being tried on an experimental basis, and has shown promise, although it will have to be used very carefully in order to prevent build up of resistance in the pest. Appropriate botanical pesticides, for example commercial formulations of neem, are available and could be used in the first instance, as an excellent replacement to the synthetic chemicals being used presently by our farmers. Apart from all the advantages and safety aspects of botanicals as compared to synthetics, it will also give farmers the necessary psychological satisfaction of having sprayed at least some product to protect their crucifers. This will have the important benefit of helping to reduce the present excessive use of synthetic insecticides which has been causing concern for sometime now, and which is not compatible with the biological and microbial components of an IPM package. Introduction of specific egg and pupal parasitoid(s), pathogen(s), incorporation of suitable cultural practices such as intercropping, trap crops, crop rotation, physical traps, would complete the package for the integrated management of Plutella xylostella in Mauritius.

REFERENCES ALAM M. 1992. Diamondback moth and its normal enemies in Jamaica and some other Caribbean islands. p. 419 - 426. In : Talekar NS ed. Proceedings Second International Workshop, Management of diamondback moth and other crucifer pests. Tainan, Taiwan : AVRDC. 1990. BURANDAY RP and RAROS RS. 1973. Effects of cabbage-tomato intercropping on the incidence and oviposition of the diamondback moth Plutella xylostella (L.). Phillipines Entomologist 2 : 369 - 374. FACKNATH S. 1996. Application of Neem extract and intercropping for the control of some cabbage pests in Mauritius. Proc. International Neem Conference, Queensland, Australia, Feb. 1996 In Press. FACKNATH S. 1997. Study of botanical pesticides in Mauritius. Proc. Expert Group Meeting on risk reduction in agrochemical development in the Afr0-Arab region. Dec. 1996, Mauritius. GOOLAUB A. 1995. Study of a Bacillus thuringiensis formulation for the control of some important lepidopteran pests of agriculture.BSc Thesis. Reduit : University of Mauritius. MANR see under Ministry of Agriculture and Natural Resources MINISTRY OF AGRICULTURE AND NATURAL RESOURCES. 1995. Le guide du petit exploitant. Mauritius : Ministry of Agriculture and Natural Resources. 128 p. NAKAHARA LM, McHUGH J, OTSUKA CK, FUNUSAKI GY and LAI PY. 1986. Integrated control of diamondback moth and other insect pests using an overhead sprinkler system, an insecticide and biological control agents on watercress farm in Hawaii. p. 403 - 413. In : TALEKAR NS and GRIGGS TD eds. Proceedings First International Workshop, Diamondback moth management. Shanhua, Taiwan : AVRDC,. 1985. AMAS 1997. Food and Agricultural Research Council, Réduit, Mauritius 107


RAMGOOLAM P. 1976. A preliminary investigation to assess the potential of Bacillus thuringiensis for control of Crocidolomia binotalis Zell. BSc Thesis. Reduit, University of Mauritius. RIETHMACHER, ROMBACH and KRANZ. 1992. Epizootics of Pandora blunkii and Zoophtora radicans in diamondback moth population in the Phillipines. p. 193 - 202. In : Talekar NS ed. Proceedings Second International Workshop, Management of diamondback moth and other crucifer pests. Tainan, Taiwan : AVRDC. 1990 SIVAPRAGASAM A, TEES SP and RUWAIDA M. 1982. Effects of intercropping cabbage with tomato on the incidence of Plutella xylostella. MAPPS Newsletter 6 (2) : 6 -7 . SRINIVASAN K and KRISHNAMOORTHY PN. 1991. Indian mustard as a trap crop for major lepidopterous pests on cabbage. Tropical Pest Management 37 (1) : 26 - 32. SRINIVASAN K and KRISHNAMOORTHY PN. 1992. Development and adoption of integrated pest management for major pests of cabbage using indian mustard as a trap crop. p. 511 - 521. In : Talekar NS ed. Proceedings Second International Workshop, Management of diamondback moth and other crucifer pests. Tainan, Taiwan : AVRDC. 1990. TABASHNIK BE, CUSHING NL, FINSON, JOHNSON MW. 1990. Field development of resistance to Bacillus thuringiensis in diamondback moth (Lepidoptera : Yponomeutidae). Journal of Economic Entomology 83 : 1671 - 1676. TALEKAR NS, LEE ST and HUANG SW. 1986. Intercropping and modification of irrigation method for the control of diamondback moth. p. 145 - 152. In : TALEKAR NS and GRIGGS TD eds. Proceedings First International Workshop, Diamondback moth management. Shanhua, Taiwan : AVRDC,. 1985. WAKISAKA S, TSUKUDA R and NAKASUJI F. 1992. Effects of natural enemies, rainfall, temperature and host plants on the survival and reproduction of diamondback moth. p. 15 26. In : Talekar NS ed. Proceedings Second International Workshop, Management of diamondback moth and other crucifer pests. Tainan, Taiwan : AVRDC. 1990 WATERHOUSE DF. 1992. Biological control of diamondback moth in the Pacific. p. 213 - 222.. In : Talekar NS ed. Proceedings Second International Workshop, Management of diamondback moth and other crucifer pests. Tainan, Taiwan : AVRDC. 1990.

COMMENTS Q.

What is the recommended method of control of Plutella xylostella?

A.

The Ministry recommends the use of chemicals depending on the severity of the attack. In case where parasitoids have been released, botanical pesticides can be used, but these have a short life period owing to their sensitivity to light.

Q.

Can Plutella be controlled by overhead irrigation?

A.

Plutella has been known to have low populations in cold regions, tolerant varieties plus irrigation should give control in these regions.

Q.

What is the Brassica spp that is used as trap plant?

A.

Indian mustard is used but there is a strong influence of variety.
