SHORT COMMUNICATION

Fitness traits of insecticide resistant and susceptiblestrains of tea mosquito bug Helopeltis theivoraWaterhouse (Heteroptera: Miridae)_286 229..232

Somnath ROY1, Ananda MUKHOPADHYAY1 and Guruswami GURUSUBRAMANIAN2

1 Entomology Research Unit, Department of Zoology, University of North Bengal, West Bengal, India2 Departments of Zoology, Mizoram Central University, Mizoram, India

Correspondence

Somnath Roy, Entomology Research Unit,Department of Zoology, University ofNorth Bengal, Darjeeling-734 430, WestBengal, India. Email:entosomnath@rediffmail.com

Received 21 February 2010;accepted 31 March 2010.

doi: 10.1111/j.1748-5967.2010.00286.x

Abstract

We compared the biological traits of insecticide resistant and susceptible fieldpopulations of tea mosquito bug Helopeltis theivora Waterhouse. The insecticideresistant population of the conventional Tea Estate “Chuapara” of the Dooars,Jalpaiguri, differed significantly from the susceptible strain of the organic TeaEstate “Makibari” of Darjeeling. Both these tea plantation areas are located inthe northern part of West Bengal, India. Adverse changes in biological and devel-opmental traits were observed mainly in: (i) reduction in oviposition period;(ii) fecundity; and (iii) prolongation of nymphal and total developmental period.However, all other parameters such as pre- and post oviposition periods, eggincubation period, hatchability and adult longevity were not significantly different.These results clearly demonstrated that only certain fitness components in theresistant strains appear to be adaptively changed and lowered.

Key words: fitness traits, Helopeltis theivora, insecticide resistance, tea mosquito bug.

Introduction

The tea mosquito bug Helopeltis theivora Waterhouse is amajor pest of horticultural crops throughout the world,causing huge crop losses, particularly to tea plantations inNorth East India (Gurusubramanian et al. 2008). The croplosses due to H. theivora may often reach 100% (Roy &Mukhopadhyay 2009). The pest is considered difficult tomanage in most parts of North East India because it candevelop resistance quickly to insecticides applied in its man-agement. It has developed resistance to almost all conven-tional non-pyrethroid insecticides used for its control (Bora& Gurusubramanian 2007; Roy et al. 2009a). Insecticideresistance leading to control failure is now common in theDooars tea plantation of North Bengal, India.

Insecticide resistance in insects often involves deficien-cies in fitness, vigor, behavior or reproductive potential.Reduced biotic fitness of resistant phenotypes has beenreported in several species of insects. Resistant strains of

arthropods often have lower fecundity and longer develop-mental time than their susceptible counterparts (Georghiou& Taylor 1977). The temephos (organophosphate com-pound) resistant strain of southern house mosquitoshowed lower fecundity, took more time to complete devel-opment and had poorer viability than the susceptible strain(Ferrari & Georghiou 1981). Egg production, hatchability,mating success and adult viability were lower in resistantHawaiian strains of Plutella xylostella (Groeters et al.1994). However, a Bacillus thuringiensis resistant popula-tion of Plutella xylostella in Florida did not show any fitnesscost (Tang et al. 1997). Information on the fitness cost ofresistance in populations of H. theivora is not available.

Therefore, in the present study, an attempt has been madeto compare the biological traits of insecticide resistant fieldpopulations with that of the susceptible strain of H. theivora.The susceptible strain of H. theivora was brought fromthe organic plantation at Makibari Tea Estate, Darjeelingslope, West Bengal, India, which has never been treated with

Entomological Research 40 (2010) 229–232

© 2010 The AuthorsJournal compilation © 2010 The Entomological Society of Korea and Blackwell Publishing Asia Pty Ltd

synthetic pesticide in its history. The resistant population ofH. theivora was collected from the Chuapara Tea Estate,Jalpaiguri, West Bengal India, which is a conventional teaplantation of the Kalchini tea sub-district of the Dooarswhere pesticide consumption was very high (Roy et al.2008a). Besides this, Bora et al. (2007) and Roy et al.(2008b) noted that commonly used conventional insecticideswere on average 50 to 350 times less toxic to the Dooarspopulation than the Darjeeling population.

Materials and methods

Thirty newly emerged adults of the resistant and susceptiblepopulation of H. theivora were kept separately in threegroups inside hurricane lamp glass chimneys with the mouthcovered with a nylon mesh for aeration. Two to three healthyTocklai vegetative tea clone (TV1) tea shoots (with threeleaves and a bud) were kept with their bases immersed inwater-filled glass vials (2 cm long ¥ 1 cm diameter) througha cotton plug. The vials were placed on a Petri dish (12 cmdiameter) with paper toweling. The whole set-up wascovered by the glass chimney and maintained in the labora-tory at 25 � 2°C, 70–80% relative humidity and underphotoperiod conditions of 16 h light : 8 h dark (LD 16:8).Three male and three female individuals of each strain wereintroduced into the glass chimney. Five such replicationswere studied in every strain. Mated females were allowed tooviposit on the shoots and the egg-laden shoots wereremoved. By using a strong magnifying glass, micropylarprocesses (in the form of hairs) of eggs could be seen stick-ing out from the plant surface where they had been inserted.The bases of the egg-laden twigs were kept immersed inglass tubes to avoid desiccation. Fresh tender shoots wereprovided in the tube until the emergence of the nymphs.Water mixed with carbendazim 0.1% was added to preventfungal growth on the shoots. Observations of hatchabilitywere recorded cumulatively up to 28 days (Roy et al.2009b). Those eggs that did not hatch after this period wereregarded as nonviable. Newly emerging first instar nymphswere transferred individually to a Petri dish (10 cm diam-eter) and were daily provided with tender host shoots moist-ened with wet cotton around the petiole. Third instar nymphs(n = 10) were reared in each glass chimney. The shoots andthe glass chimney were replaced every day. Nymphs werecarefully removed from old shoots using a camel hair brushand transferred to new shoots. This process continued untiladults emerged. The life history traits of pre-ovipositionperiod (PreOP, days), oviposition period (OP, days), post-oviposition period (PoOP, days), fecundity (FD, no. of eggslaid/female), incubation period (IP, days), hatchability (HC,% of egg hatch), total nymphal duration (TND, days), totaldevelopmental time (TDT) i.e. egg to adult (days), sex ratio

(SR, female: male) and average longevity (AL) of both maleand female (days) were recorded from such a culture.

Significant difference among the biological traits of thetwo populations was determined using a Tukey multiplecomparison test.

Results and discussion

A resistant population diverts more body resources tovarious resistance mechanisms to overcome the toxic effectsof insecticides. This may often result in some biologicaldeficiencies in the resistant populations when comparedwith the susceptible populations. Hence, in the present study,the biological traits of insecticide-resistant field populationswere compared with those of the susceptible population ofH. theivora. The results of this study are presented inTable 1. Of eleven biological parameters, only four (ovipo-sition period, fecundity and nymphal and total developmen-tal duration) were found to be adversely affected in theresistant population of H. theivora. On the other hand, nosignificant differences in other parameters were observed inboth the test populations (Table 1).

The mean oviposition period of the resistant populationwas 22.7 days, whereas the corresponding figure for thesusceptible strain was 20.3 days (Table 1). Therefore, theresistant population was significantly different from suscep-tible population of H. theivora with respect to this param-eter. That females of Helicoverpa armigera with changes inoviposition periods had a relatively higher tendency todevelop resistance to insecticides has been observed byvarious workers (Forrester et al. 1993; Glenn et al. 1994;Xia et al. 2001. These differences are probably due to thereproductive disadvantages in the resistant female (Donget al. 1996).

The average fecundity of the resistant population was135.4 (70–171) (Table 1), but the corresponding values forthe susceptible population was 170.2 (103–201). It isevident from the data that the fecundity of the resistantpopulation was significantly reduced in comparison withthe susceptible strain. Similar findings, that resistant Plu-tella xylostella females produce fewer eggs than the sus-ceptible strain, were also reported by Groeters et al. (1994).Further, Sayyed and Wright (2001) also reported that sig-nificantly fewer eggs were laid by the Cry I Ac selectedstrain compared to the unselected ROTH strain of P. xylos-tella. A significant reduction in the fecundity of resistantfemales of Helicoverpa armigera has been reported byCampanhola (1988), who reported that resistant femalesproduced 1200 eggs each compared to 2500 eggs per sus-ceptible female. It has also been suggested that the reducedfecundity was the consequence of metabolic resistance toinsecticides. The present findings, thus, fall in line with theresults of these workers. The reduction in the rate of egg

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230 Entomological Research 40 (2010) 229–232© 2010 The Authors. Journal compilation © 2010 The Entomological Society of Korea and Blackwell Publishing Asia Pty Ltd

laying in the resistant population might have resulted fromless energy partitioning for reproduction. The major shareof the metabolic energy was possibly allocated and used indeveloping biochemical and physiological defenses relatedto detoxification of the insecticide (Price 1974; Ribeiroet al. 2001).

Prolongation of the mean total nymphal and developmen-tal duration was noticed in the resistant population comparedto the susceptible population (Table 1). The results are inagreement with the findings of Trisyono and Whalon (1997)who also reported significantly longer larval development ofa resistant strain of Colorado potato beetle than that of itssusceptible strain. Similarly, Sayyed and Wright (2001)found variation in development time between the selectedand unselected Malaysian strains of Plutella xylostella.Similar results were also reported by Georghiou and Taylor(1977) who reported resistant strains of arthropods oftenhave longer developmental time than their susceptiblecounterparts.

It seems that the resistant forms of H. theivora developedcertain life cycle traits such as longer nymphal developmen-tal period, prolonged oviposition period and lower fecundityin order to adapt to low levels of available metabolic energyand to withstand the stressed conditions resulting fromrepeated pesticide exposure.

References

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