Development and non-preference of Sitophilus zeamais on, stackburnt' maize

Transcription

1 of the 7th niernaiional Workmg Conferene on Stored produt ProtetuJn Volllme 1 Development nonpreferene of Sitophilus zeamais on, stakburnt' maize D P Giga J Canhao1 The haratensti disoloration of the germ penarp represents a form of heat damage S reogmsed as a feature of 'dry gram heatmg ' as distint from the well known 'damp gram heatmg ' (Tyler, 1992) Expenmental data from the Natural Resoures nstitute (NR) has shown that the disoloration results from moisture temperature dependent hemial reations, part of whih may be nonenzymi brownmg CPhillrps Donaldson, 1994) nreased disoloration S haratensed by a redution m lysine a onversion of surose to reduing sugars WhCh may subsequently at as reatants m further hemial omplexes Stakburmng of maize auses a redution m the nutntive value for all lasses of livestok an be predited to do so for humans as well Pamgrahi et al (1996) n the ase of insets, SltophLlus zeamms Tribolium. asitmeum development times, survival of Fl progeny multiphation rates were adversely affeted on stakburnt maize when ompared to normal maize (Giga, 199, Tanyongana Nyanongo 199) Expenmental stak data from Zimbabwe has shown that stakburn progression S haratensed by rapid internal heating of polypropylene bagstaks to a maximum of 40"( maintenane of temperatures at this level, With only mmor flutuations, throughout storage (Conway, 1996) The auses of the rapid built up of mternal stak temperatures are unlear, though insets have been mpliated (Kennedy Devereau, 1994, Conway, 1996) Kennedy Devereau (1994) also observed a temperature limit of 40 C m staks followed by oohng after fumigatons to varymg degrees m expenmental staks The lethal temperature for SztophLlus spp Tnbolwm spp, the msets WhCh were found m greatest numbers m the samples, are reported by vanous authors (Howe, 1962a, Reddy, 190) as 40 C Howe (l962b) proposed a proess by whih mset heatmg m gram may progress An mset mfestatlon m the gram respres produes heat, ausmg a nse m temperature whih m turn mreases the reprodutve rate metaboh rate of the msets The mfestaton thus grows at an aeleratmg rate, releasmg heat at an aeleratmg rate resultmg m greater temperature nses ThS proess ontmues untl the temperature beomes unfavourable for the msets they either mgrate or die Whether the msets migrate bak mto stakburnt gram Abstrat Maize stakburn has emerged as a signifiant threat to food seunty m subsaharan Afria m the last deade resulting m sigrufiant losses ommerially stored maize Stakburnt maize S haratensed by a moderate to severe reddishbrown disoloration of the kernel germ of maize resulting from heat buildup m the mtenor of polypropylene bag staks Stakburn auses a redution m the nutritional value of the gram A omparative study of the development of the maize weevil, Suophslue zeamms, on normal stak burnt maize showed signifiant differenes m progeny emergene, mean duration of development mdies of suseptibility between the two maize types An index of suseptibility of 12 34± 0 14 was reorded for normal maize while that for stakburnt maize was 9 29 ± 0 n freehoie tests weevils strongly seleted normal maize, mludmg adults whih had been onditioned on stakburnt maize ntrodution n Zimbabwe, large quantities of white maize (more than 1 2 rmlhon tonnes, annually) are suessfully stored outdoors m modular 000 tonne staks These are built on a dunnage of poles are overed with tarpaulms Woven polypropylene saks have replaed Jute saks (m the late 1980s) are now used for maze storage Dunng reent years, omdmg With the mtrodutlon of woven polypropylene saks, maze throughout the entre of some bagstaks have been found to be dsoloured from a light tan through to a dark redbrown olour after storage (Tyler, 1992) The disoloraton, termed stakburn, results m the affeted maize bemg downgraded With attendant fmanclal losses Stakburn has also ourred frequently m food ad maize m several ountres mludmg Angola, Mozambique, Swazl1 Zambia (Phl1hps Donaldson, 1994) 1 Department of Crop Siene, Umverslty of Zimbabwe 13

2 of the 7th nternatw'hal Worktng Conferene on Storedprodut Materials Methods Samples of stakburnt normal maize were olleted from the Gram Marketing Board Depot m Mvurwi for the expenments The maize was stored m a old room pnor to the start of the experiments, subsamples were Withdrawn frozen for two weeks to dismfest the gram Thereafter, the gram was equihbrated to 70% r h 28 C Expenments were onduted m sealed plasti boxes plaed m an inubator set at the expenmental temperature The humidity was mamtamed using sodium hlonde solutions Results Disussion Development ndies of Suseptibility The mean development penod (days), mean number of adults emerged the mean suseptibihty mdies are shown m Table 1 Compansons of data using Student ttests showed srgrufiant differenes (p < 0 01) between the two maize types for all the parameters measured Development times of weevils were sigruhantly longer on stakburnt maize With signifiantly fewer insets developing on this maize Similarly the index of suseptibihty of stakburn maize (9 29) was signifiantly lower than normal maize (12 34) These data mdiate that stakburnt maize S nutritionally' mfenor ' for weevil development survival Other workers (Tanyongana Nyanongo, 1996, Allotey Odamtten, 1996) have shown multipliation rates of several speies of storage insets to be signifiantly lower on stakburnt maize ompared to normal maize Whether tlus differene was due to mreased development times on stakburn maize or redued oviposition m the more "brittle' stakburn maize S not known Sme the stakburnt maize was equihbrated to the same moisture ontent as the normal maize m the urrent study, the lower emergene rate, delayed development lower suseptibility index may be attnbuted to some other fator (s ) besides the moisture ontent Development indies of suseptibihty Fifty grams of maize were plaed m small glass Jars for eah maize type infested With pairs ( males females) of newly emerged (approximately lweek old) adults The insets were left to OViPOSit on the gram for one week under the expenmental onditions after three weeks dally observations were made noting the daily emergenes By reording the daily emergenes the mean development times of the emerged insets from the time of infestation were alulated An index of suseptibihty for the two maize types was alulated usmg the formula (Doble, 1974) ndex = lin no progeny /mean development time /,0 The expenment was repliated ten times experiments: VoLume 1 n eah ase, one petndish (9m diameter) filled With normal maize another With stakburnt maize were plaed at opposite ends of the plasti boxes to whih fifty weevils were introdued m the entre The boxes were then sealed mmediately plaed m darkness m an inubator The numbers of weevils inside the petndishes ontammg the two types of maize outside the dishes were ounted 1, 2, 4, 8 24 hours after mtrodution Five repliates of eah treatment were set up With the expenment being repeated twie Thus there were ten repliates for eah treatment one ooled Snot known The objetives of this study were ) to deternune whether S zeanuu8 adults, m laboratory hoie tests, showed any preferene for stakburnt maize 11) to ompare the development of the mset on stakburnt normal maize Choie tests Protetwn Preferene/non preferene A senes of hoie tests were onduted to determme whether there are any differenes m the seletonof normal stakburnt maize by weevils that had reeived different ondltomng treatments The followmg tests were performed ) white vs stakburn maize usmg unonditioned weevls, 11) yellow vs stakburn maze usmg unonditionedweevils, m) white vs stakburn mazeusmg weevils onditioned on white maize, V) white vs stakburn mazeusmg weevls onditioned on stakburn maize, V) white vs stakburn maize usmg a mixture (1 1 ratio) of weevls onditioned on white stakburn maize All tests were onduted at 28 C m sealed plasti boxes (m /, 14m ;< Bm) usmg maize equilbrated at 70% r h 28 C The weevls were onditioned on the appropnate maze types under the expenmental onditions for three days before use m the tests Table 1. Mean development penod, emergene mdles of suseptibilty of Sttophllus zeanuts on normal stakburnt maize MaZe Type Devpt penod (days) Normal Stakburnt tvalues DF 36 3± ± No adults emerged 89 0± ± Suseptibilty mdex 12 34± ± Preferene/nonpreferene tests Figures 1 shows the numbers of weevls found on stakburnt normal maize With time The figures learly show a preferene by the weevils for the normal undamaged 14

3 of the 7th nternatumal Worhng Conferene on. St01'eClp1'Odut Protetion Volume 1 maize Chisquare tests for all the experiments. rrespetive of the ondrtionmg of the insets showed signifiant deviations from the 1 1 ratio nitially there was a small differene in the number of msets reorded on both maize types but With time sigrufiantly more weevils were reorded on the normal maize ompared to the stakburnt maize Conditiomng adults on stakburnt maize did not sigmfiantly affet their behaviour when given a hoie of the two types of maize All insets showed a strong preferene for the normal, undamaged maize 40 \ :i e:l e 20 : ::i! norma'i slbum Fig. l. 0 1hr 2hr 4hr 8hr Tme Mean number of weevils on normal stakburnt maize using unonditioned weevils e:: Cl ::i! ~~ slburn sr_l 01_+' 1hr 2hr 4hr 8hr 24hr Fig. 2. Mean number of weevils on normal yellow stakburnt maize using unonditioned weevils i

4 Proeedmqs of the 7th lniernaiumal Warkmg Conferene Oil Storedprodui Protetion Volume 1 4 r 40 t 1.. G,g E ~.. 20 G ::!: r=+= norrnall l::!s/bumj t t j ol_ 1hr 2hr 4hr 8hr 24hr Fig. 3. Mean number of weevils on normal stakbumt maize ondinoned on stakbumt maize 40.8 E ~ 20 : :E _.::+ normal slbum 0 lhr 2hr 4hr 8hr 24hr Fig. 4. Mean number of weevils on normal stakbumt maize onditioned on normal marze 16

5 Proeedmqs of the 7th nternational Wmkmg Conferene on Storedprodut Proietum Volume 1 ~ e E! normal ~...~~sjbum 20 ~ o._+1hr 24hr 8hr 4hr 2hr Tme Fig.. Mean number of weevils on normal stakbumt maize onditioned on both types of maize Expenmentahs Howe, R W Referenes et Apphata, 1962b aused by msets Allotey, J multiphation, Odamtten, G food preferene, T Kennedy, nset Asperqillus ontammant L speies damage aused by Cryptolestes ferruqineu«, largesale domuua, Suophilue zeamms to normal stakburnt maize m Ghana n Odamtten G Wnght, T Rhyzopertha Clerk G C (eds ) nvestigation maize m subsaharan stakburn workshop Otober Afna 3 November, Parugrahi, 199, University projet P Third Annual Report on ECDGX suseptibility The laboratory assessment of maize varieties Phillips, of the mherent to postharvest mfestation Siiopiuius zeamms Journal of stored Produts, Giga, D P 199 Development of Siioplulu«zeamalS on Clerk G C (eds ) maize m subsaharan disruption Afna Tenebnomdae) G T m at suboptimal the larvae (Herbst) of a workshop temperatures pupae Highley, B R on woven E, (eds ) Workmg Conferene LA, Davies, R Wood, C S Donaldson, T J Report No Harare, Zimbabwe, UK Natural Resoures Chatham, Eologial studies of the rie weevil 42, Tanyongana, R Nyanongo, R C 199 A ompanson of mset development on normal stakburnt maize n Odamtten G T Clerk G C (eds ), nvestigation on maize stakburn maize m subsaharan Afria 199, Uruversity of Ghana, 3 astaneum Protetion Journal of Eonomi Entomology, on maize stakburn n Champ, of the 6th nternational S, Bestwik, nstitute Reddy, D B of a workshop Observations on the rate of growth of moultmg Tribouuni Odamtten nvestigation Otober 3 November, 7 Howe, R W 1962a n H J Observations m jute m Zimbabwe saks E J, Banks, NR Report R2140 (S) by normal maize 1994 storage ECDGX Researh Projet Workshop, Researh, stakburnt maize 0, 137 D 1996 The nutritrve value of stakburned yellow maize for livestok tests m 1n mtro in broiler hiks British Journal of Nutntion, 76, Dobie, P 1974 A D Devereau, on Storedprodut of a of Ghana Conway, J A (ed ) 1996 Annals of Applied Biology, outdoor polypropylene on maize, A study of the heatmg of stored gram Otober 3 November, 199, Urnversrty of Ghana, of Tyler, (Coleoptera P S 1992 Heat disoloration World Gram, September, Entomologia of bagged maize