Preferential feeding of an anthocorid predator Blaptostethus pallescens Poppius on different stages of cotton mealybug

Gupta Tripti，Ballal Chandish R.，Joshi Sunil(National Bureau of Agriculturally Important Insects(ICAR)，H．A．Farm P．O.，Bellary Road，Bangalore 560 024，India)

1 Introduction

The solenopsis mealybug Phenacoccus solenopsis Tinsley has emerged as a serious pest on cotton in India．This polyphagous pest(attacking Gossypium hirsutum Linn.，Vigna radiata Linn．Cyamopsis tetragonoloba(Linn.)，Capsicum annum Linn.，Lycopersicon esculentum Mill． HelianthusdebilisLinn．etc.)is considered to be an introduced pest，first collected and described in New Mexico in 1897 and reported to have entered into India from Pakistan(A-non.，2006)．Mealybug infestation was recorded in all the nine cotton growing states of India viz.，Punjab，Haryana，Rajasthan，Gujarat，Madhya Pradesh，Maharashtra，Tamil Nadu，Andhra Pradesh and Karnataka and 30 to 40 percent loss in cotton yield was reported(Dhawan et al.，2007;Dharajothi et al.，2008)．

The solenopsis mealybug attacks growing parts，main stems and branches．The growing parts become bunchy and affected plants remain underdeveloped producing fewer flowers and bolls of a smaller size．Black sooty mold grows on mealybug infested plant parts．The severely affected plants show blackish symptoms similar to burning of leaves．Management strategies like chemical and cultural control are not very effective due to the waxy body covering of mealy bugs(International Cotton Advisory Committee，2008)．Therefore，using biological control agents for the control of mealy-bugs is considered to be a useful option．Anthocorids are known to be potential predators of several pests on different crop ecosystems(Muraleedharan＆Ananthakrishnan，1978)．Blaptostethus pallescens(Poppius)(Hemiptera:Anthocoridae)，originally described asBlaptostethuspiceus(Fieber)var．pallescens(Poppius)from Celebes，was reported as a potential predator of mites in grain ware houses and pests of maize in Egypt(Tawfik ＆ El．Hussein，1971;Tawfik et al.，1974)．In India，B.pallescens was recorded from TamilNadu， Maharashtra(Muraleedharan，1977)and Karnataka(Jalali ＆ Singh，2002)．B.pallescens was identified as a potential predator of maize aphid Rhopalosiphum maidis(Fitch)，eggs and early instar larvae of Spodoptera litura(Fabricius)and Helicoverpa armigera(Hubner);Tetranychus urticae(Koch)(Ballal et al.，2009)and sucking pests like cotton aphid Aphis gossypii Glover and cabbage aphid Brevicoryne brassicae(Linnaeus)(Ballal et al.，2003)．

Very few records are available of anthocorids as predators of mealybugs．Cardiastethus exiguus Poppius(Hemiptera:Anthocoridae)was observed to be a predator of the notorious pest cassava mealybug Phenacoccus manihoti Matile－Ferrero in Republic of Congo(Fabres et al.1980)．Anthocoris muraleedharani Yamada，sp．nov．was recorded on Bauhinia purpurea L.predating on Ferrisia virgata(Cockerell)at Bangalore(Yamada et al.，2010)．B.pallescens was recorded on Rastrococcus iceryoides(Green)infested Lagerstroemia flos reginea(Bungor)and cotton mealybug(CMB)infested cotton at Bangalore and Pune，respectively in India．Laboratory trials indicated that B.pallescens could predate on the cotton mealybug(Ballal et al．2011)．Through the present study，an attempt was made to understand the preferential feeding of B.pallescens on different stages of CMB and to identify the potential stage of the predator which could be used for targeting the pest.

2 Materials and Methods

Cotton mealybugs were reared on sprouted potato tubers in the mass production laboratory at the National Bureau of Agriculturally Important Insects(NBAII)(ICAR)，Bangalore，India．B.pallescens was cultured in the laboratory following the techniques developed by Ballal et al． (2003)．Ovisacs，young and mature crawlers and adults of cotton mealybugs and B.pallescens mature nymphs and adults which were used for the present study were obtained from the Mass Production Laboratory at NBAII．

2.1 Evaluation of B.pallescens against cotton mealybug ovisacs/neonates

One P.solenopsis gravid female was transferred on to a sprouted potato tuber placed inside a ventilated round plastic container(15cm diameter x 5 cm height)for egg laying．The base of the plastic container was lined with a layer of tissue paper．The container was covered with a black cloth and then closed with a lid．After 24h，the P.solenopsis female was removed．One mature B.pallescens(5－day－old)nymph，which was fed for the first four days on Corcyra cephalonica(Stainton)eggs was released into the container which contained an ovisac of cotton mealybug．The set up was replicated six times for testing the predatory potential of nymphal stage and repeated for the adult stage．A control batch was maintained with CMB ovisac but without releasing B.pallescens nymph/adult．After one week of release，the number of mealybug crawlers in each replication was counted in treatment and control batches．Data obtained was subjected to one way ANOVA.

2.2 Feeding preference of B.pallescens on different stages of cotton mealybug

Fixed numbers of young P.solenopsis crawlers(20)were released with one B.pallescens mature nymph on a cotton leaf，placed in a ventilated round plastic container(15cm diameter x 5 cm height)．The base of the plastic container was lined with a layer of tissue paper．The petiole of the cotton leaf was covered with wet cotton wrapped in aluminum foil in order to keep the leaf fresh．The container was covered with a black cloth and closed with a lid．A control batch was also maintained consisting of similar arenas of mealybugs，but without the anthocorid predator．At 24h intervals，the leaf was removed and dead crawlers were counted in the treatment and control batches．Fresh cotton leaf with crawlers was provided in the container with B.pallescens nymph as well as in the control batch．Nine replications were maintained for each of the treatment and control batches．The same set－up was repeated with B.pallescens nymph against mature cotton mealybug crawlers and adults．The set was again repeated for B.pallescens adult against young and mature CMB crawlers and CMB adults.

The observations on feeding potential were recorded for the nymphal stage till adult was formed and in the case of adult till its mortality．Per day and total feeding by B.pallescens on different stages of cotton mealybug was based on the corrected mortality of mealybugs in the treatment batches in comparison to the control．Data obtained was subjected to two － way ANOVA.

For day－wise feeding potential of B.pallescens the most preferred stage of the prey ie．young CMB crawlers were provided．5－day－old B.pallescens nymph was used for the experiment．The observations were recorded on day－wise feeding potential of B.pallescens nymph till the adult mortality．Control batch was also maintained with young CMB crawlers(without B.pallescens nymph)．B.pallescens per day feeding on young CMB was based on corrected mortality of mealybugs in treatment in comparison to the control．It was replicated nine times．

2.3 Evaluation of B.pallescens against young cotton mealybug crawlers at different ratios

B.pallescens nymph and adult were released at different predator:prey ratios 1∶5，1∶10，1∶15 and 1∶20 against 4－5－day－old crawlers of cotton mealybugs．The experimental procedure followed was similar to the one for evaluation of B.pallescens against CMB ovisacs/neonates． In this experiment， young crawlers(4－5－day－old)were released on potato tubers for measuring the predatory potential at different ratios．Following treatments were set up.

1 B.pallescens nymph:5 mealybug crawlers

1 B.pallescens nymph:10 mealybug crawlers

1 B.pallescens nymph:15 mealybug crawlers

1 B.pallescens nymph:20 mealybug crawlers

1 B.pallescens Adult:5 mealybug crawlers

1 B.pallescens Adult:10 mealybug crawlers

1 B.pallescens Adult:15 mealybug crawlers

1 B.pallescens Adult:20 mealybug crawlers

A control batch was maintained with the same number of mealybugs， but without releasing B.pallescens nymph or adult．Each treatment was replicated thrice．Data obtained was subjected to one way ANOVA.

3 Result and Discussion

3.1 Evaluation of B.pallescens against cotton mealybug ovisac/neonate

B.pallescens nymphs and adults were evaluated against cotton mealybug ovisacs/neonates．After one week of release，10.50 and 3.67 mealybug crawlers were recorded in the treatment with B.pallescens nymph and adult，respectively，while in the control，45.5 crawlers were recorded(Table1)indicating that B.pallescens nymph and adult stages could effectively predate on the CMB neonates．Cotton mealybug has a high reproductive rate and so it is essential to control this pest at an early stage．In the present study，in comparison to control，there was a 76.9 and 91.6%reduction in the population of CMB crawlers in the treatments with B.pallescens nymph and adult，respectively．However，both the treatments were statistically on par with each other(Table 1)．

Table 1 Evaluation of B.pallescens against cotton mealybug ovisacs/neonates

3.2 Feeding preference of B.pallescens on different stages of cotton mealybug

Laboratory trials indicated that young nymphs(3 to 4 day old)of B.pallescens were not effective in predating on young crawlers of CMB，which is in agreement with studies conducted by Ballal et al．(2011)．Hence in our experiment，B.pallescens nymph was ini-tially fed for the first four days on Corcyra eggs and then on CMB crawlers．However，an anthocorid predator A.muraleedharani could predate on CMB crawlers right from its early nymphal stage(Ballal et al.，2011)．

Irrespective of cotton mealybug stages，mature B.pallescens nymph fed on significantly more number of crawlers(30.5)in comparison to adult(21.67)(Table 2)．Irrespective of its stage，B.pallescens preferred to feed on young cotton mealybug crawlers．B.pallescens fed on 33.17 and 19 young and mature crawlers， respectively． This indicates thatmature nymphs and adult B.pallescens could effectively predate on both young and mature CMB crawlers，however，preference was more for younger mealybug crawlers and the mature nymphal stage of B.pallescens was observed to be more voracious than the adult stage．It was also recorded that the anthocorid could not feed on the adult mealybugs．The reason for non preference of adult mealybugs by B.pallescens may be its relatively small size in comparison to the large size of prey and also the increased waxy coating in the adult mealybug．

It has thus emerged that mature nymph and adult could predate equally well on ovisacs/neonates as well as on mature CMB crawlers．However in the treatment where young CMB crawlers were provided as feeding，mature B．pallescens nymph was observed to be significantly more voracious then the adult．The anthocorid could not feed on adult mealybugs(Table 1＆2)．

Table 2 Feeding preference of B．pallescens on different stages of cotton mealybug

Some reports indicate that adult stages of predators are more voracious．Garcia et al．(2009)and Ghafoor et al．(2011)observed that adult stage of Cryptolaemus montrouzieri Mulsant was a more efficient predatory stage as compared to the adult stage．

The day－wise predatory potential of B.pallescens adult and nymph is depicted in Fig 1．B.pallescens nymph and adult fed on 0 to 4 and 0－6 CMB crawlers per day，respectively．Mean feeding per day was about 2.24 crawlers in the case of B.pallescens nymph，and 1.96 in the case of adult．In the case of B.pallescens nymph，the highest peak in feeding was observed on 16thday(Fig.1)．An extended nymphal period of 23 days was recorded when B.pallescens was reared on CMB，while on C.cephalonica eggs the nymphal period was 15 days(Ballal et al.，2003;Gupta，2009)．In the case of B.pallescens adult，highest peak in feeding was observed on the first day and lowest was observed on 17thday just prior to its mortality．In the present study，when reared on CMB crawlers，B.pallescens adult could live for 18 days，while this predator could survive for 2 months on C.cephalonica eggs(Ballal et al.，2003;Gupta，2009)．

3.3 Evaluation of B.pallescens against young cotton mealybug crawlers at different ratios

Fig．1 Day wise feeding of B.pallescens nymph and adult on cotton mealybugsB.pallescence nymphs were fed on C.cephalonica eggs for the first four days

B.pallescens nymphs were released at different predator:pest ratios－ 1∶5，1∶10，1∶15 and 1∶20 against crawlers of cotton mealybug．Adult release at a ratio of 1∶5 provided maximum mortality(93.3%)，which was also on par with nymphal treatments at ratios of 1∶5(86.67%)and 1∶10(80.0%)．Minimum mortality was recorded in the case of nymphal release at a ratio of 1∶20(44.52%)，which was however on par with the mortality recorded in the nymphal treatment at 1∶15 and adult release at 1∶20．However，all the treatments were superior to control with respect to pest mortality(29.87%)(Table 3)．It thus emerges that for nymphal release，1∶10 could be the optimum ratio and for the adult release 1∶5.

Table 3 Evaluation of B.pallescens against cotton mealybug crawlers

No research reports are available on the feeding potential of anthocoird predators on mealybugs．Tanwar et al．(2011)reported that 20 － 70%cotton mealybugs were parasitized by an parasitoid Aenasius bambawalei Hayat on cotton，okra，Parthenium hysteropus，Achyranthes asper etc．It is worth investigating whether B.pallescens can distinguish between parasitized and unparasitised mealybugs as it has been reported that this predator can distinguish between parasitized unparasitised lepidopteran eggs (Gupta ＆ Ballal，2007)．The present study gives an indication that anthocorid predators could emerge as potential bio－control agents of mealybugs in different crop ecosystems．However，detailed field studies are required for measuring the performance of B.pallescens against cotton mealybug attacking different crops.

Acknowledgements

The authors wish to acknowledge the financial support extended by the Cotton Mission Mode project TMC MM1 3.3．The authors are also grateful to the Director，National Bureau of Agriculturally Important Insects(ICAR)，Bangalore，for providing the research facilities.

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