The most suitable growth stage (30, 50 and 100% panicle stage, flowering and dough-filling stage) of pearl millet cultivars 3/4HK, MBH110, ICMV IS 89305 and Chalakh for the oviposition of gravid female head miners (H. albipunctella) was determined in multi- and no-choice tests. Alongside this, the oviposition preference of the pest given the choice of whole plants or methanol extracts of pearl millet panicles, leaves and stems, and sorghum panicles. Oviposition of the head miner was highest during the 30% panicle extension stage of the crop in both multi- and no-choice tests. The number of eggs deposited by the pest was highest in whole plants and filter paper treated with extracts of pearl millet panicles

Green, S V

Hall, D R

Maliki, Y

Owusu, E O

Youm, O

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72 ISMN 45, 2004sand, thereby simulating natural emergence conditionsmore closely.Findings of these studies will be helpful in enhancingthe rearing of the millet head miner in the laboratory andimprove its management in the Sahel.Acknowledgments. Support for this research wasprovided by the United Kingdom Department forInternational Development (DFID) under Grant # R6693.Opinions expressed here do not reflect those of the DFID.Authors thank entomology laboratory staff at ICRISAT,Niamey for their technical support.ReferencesGahukar RT, Guevremont H, Bhatnagar VS, Doumbia YO,Ndoye M and Pierrard G. 1986. A review of the pest status ofthe millet spike worm, Raghuva albipunctella (De Joannis)(Noctuidae: Lepidoptera) and its management in the Sahel.Insect Science and its Application 7:457–463.Kadi Kadi HA, Gilstrap FE, Teetes GL, Youm O andPendleton BB. 1998. Field evaluation, longevity, and ovipositionperiod of millet head miner (Lepidoptera: Noctuidae) in Niger.International Sorghum and Millets Newsletter 39:143–144.Nwanze KF and Youm O. 1995. Panicle insect pests ofsorghum and pearl millet: proceedings of an InternationalConsultative Workshop, 4–7 Oct 1993, ICRISAT SahelianCenter, Niamey, Niger. Patancheru 502 324, Andhra Pradesh,India: International Crops Research Institute for the Semi-AridTropics. 320 pp.Vercambre B. 1978. Raghuva spp. et Masalia sp. (Lep.:Noctuidae), chenilles des chandelles du mil en zones sahelienne.Agronomie Tropicale 33:62–79.Youm O and Owusu EO. 1998a. Assesssment of yield lossdue to the millet head miner, Heliocheilus albipunctella(Lepidoptera: Noctuidae) using a damage rating scale andregression analysis in Niger. International Journal of PestManagement 44(2):119–121.Youm O and Owusu EO. 1998b. Farmers’ perceptions ofyield losses due to insect pests and methods for assessment inpearl millet. International Journal of Pest Management44(2):123–125.Observations on Factors AffectingAttraction and Oviposition Preferencesof the Millet Head Miner Heliocheilusalbipunctella to Pearl Millet PaniclesEO Owusu1, O Youm2,3,*, Y Maliki2, DR Hall4 and SVGreen4 (1. Department of Zoology, University of Ghana,Legon, Ghana; 2. ICRISAT, BP 12404, Niamey, Niger;3. Present address: The Africa Rice Center-WARDA, BP320, Bamako, Mali; 4. Natural Resources Institute (NRI),University of Greenwich, Central Avenue, ChathamMaritime, Kent ME4 4TB, UK)*Corresponding author: o.youm@cgiar.orgIntroductionThe millet head miner Heliocheilus albipunctella is aserious insect pest of pearl millet (Pennisetum glaucum)in the Sahelian zone of West Africa. Females lay 20–50batches of about 300–400 eggs on millet heads (Bernardiet al. 1989, Nwanze and Harris 1992). Eggs normally hatchin 3–5 days and the developing larvae feed on floralglumes and flower stems thus causing yield decrease.Even though millet panicles serve as oviposition sitesfor the head miner, the mechanisms underlying this choiceremain unknown. This article reports on laboratoryexperiments to investigate factors affecting host plant andhead miner oviposition interactions.Materials and MethodsInsects. Gravid female head miners were obtained fromlight traps (Robinson traps equipped with photosentiviecells with 125W mercury vapor bulbs) located at theInternational Crops Research Institute for the Semi-AridTropics (ICRISAT) Sahelian Center, Niamey, Niger.Panicle stages tests. The most suitable panicle stage foroviposition by the millet head miner was assessed usingfive plant growth stages, ie, 30% panicle extension, 50%panicle extension, 100% panicle extension, flowering stageand dough-filling stage. Panicle stages were arrangedevenly in paper containers (27 cm height, 25 cm diameter)covered with nylon gauze. Ten adult females were usedfor a multi-choice test condition in the dark. The numberof eggs laid on each panicle stage was counted thefollowing morning. Five millet varieties were used inthree replications. Positions of three pearl millet paniclesin the cages were randomly assigned for each experiment.ISMN 45, 2004 73Table 1. Oviposition preference by millet head miner among different stages of pearl millet panicles under multi-choice andno-choice test conditions.Mean total eggs (%) ± SE______________________________________________________________________________30% panicle 50% panicle 100% panicle DoughVariety extension extension extension Flowering fillingMulti-choice test3/4HK 57.2 ± 2.48 30.3 ± 1.26 12.5 ± 3.73 0.0 0.0MBH110 70.7 ± 8.94 22.8 ±11.85 5.8 ± 2.18 0.75 0.0ICMV IS 89305 75.7 ± 0.83 16.3 ± 2.68 7.4 ± 1.31 0.0 0.0Chalakh 85.8 ± 0.71 13.9 ± 1.08 0.4 0.0 0.0No-choice test3/4HK 46.0 ± 8.52 21.0 ± 2.94 10.3 ± 1.25 3.3 ± 1.70 3.0 ± 1.41MBH110 60.7 ± 9.39 27.0 ± 4.32 12.3 ± 3.09 5.7 ± 2.06 4.0 ± 2.16ICMV IS 89305 61.3 ± 12.82 26.7 ± 6.24 14.7 ± 3.68 4.0 ± 2.45 5.3 ± 2.06Chalakh 74.0 ± 7.48 25.7 ± 4.64 17.3 ± 2.86 3.3 ± 1.25 3.0 ± 0.82Whole substrate tests. Four freshly cut sorghum (Sorghumbicolor) panicles and pearl millet panicles, leaves andstems were tested under multi-choice and no-choice testconditions. Substrates were arranged in cages asdescribed above and 10 gravid females were released intothe cages between 1800 and 1900 h. Cages were left inthe dark for oviposition. The number of eggs on eachsubstrate was counted the following morning. There werefive replications.Methanol extracts tests. Extracts from fresh sorghumpanicles and pearl millet panicles, leaves and stems weretested for oviposition stimulation under multi-choice andno-choice test conditions. Extracts were obtained byimmersing the plant material (10 g each) in 100 ml of80% methanol for 3 days in the dark. After removal ofsolid material, filter papers were soaked in the respectiveextracts. The filter papers were vacuum-dried in a hoodand then were fixed around wooden rolling pins (20 cmlength, 2 cm diameter). The rolling pins were then set upin cages as described in the preceding experiments. Tengravid females were released into the cages between1800 and 1900 h. Cages were left overnight in the darkfor oviposition. The number of eggs on each treatmentwas counted the following morning. There were fivereplications. Control trials (ie, filter paper dipped inmethanol only) were initially set up but later ignoredbecause the methanol alone did not stimulate oviposition.Results and DiscussionFemale head miner oviposition preferences for four pearlmillet varieties under multi-choice and no-choice situationsare presented in Table 1. In a multi-choice situation,irrespective of the plant variety studied, 30% panicleextension gave the highest mean percentage of eggs,followed by 50% panicle head extension, full extension,flowering stage and dough-filling stage. There were noeggs laid on the flowering and dough-filling stagepanicles. However, in a no-choice situation some eggswere laid albeit far lower than for 30% panicle stage. At 30%panicle extension, the pearl millet variety Chalakh hadthe highest number of eggs, followed by ICMV IS 89305.The mean number of eggs oviposited on differentsubstrates and their respective methanol extracts arepresented in Table 2. Among all the test treatments, pearlmillet panicles and their extracts were preferred for egglaying. However, the number of eggs laid on filter paperimpregnated with methanol extract of pearl millet panicleswas lower than for intact panicles. In no-choicesituations, eggs were not laid on the whole plant ormethanol extracts of the sorghum panicles, pearl millet74 ISMN 45, 2004Table 2. Numbers of eggs (mean ± SE) deposited by Heliocheilus albipunctella female moths on whole plant substrates or filterpaper impregnated with methanol extract under multi-choice and no-choice test conditions.Multi-choice test No-choice test__________________________________ _______________________________Substrate Plant Filter paper Plant Filter paperSorghum panicles 0.2 ± 0.18 0.0 0.0 0.0Pearl millet panicles 44.4 ± 7.38 5.4 ± 0.92 32.0 ± 2.9 16.8 ± 1.9Pearl millet leaves 0.2 ± 0.18 0.0 0.0 0.0Pearl millet stems 0.4 ± 0.36 0.0 0.5 ± 0.5 0.5 ± 0.5leaves or pearl millet stems (Table 2). This suggests theabsence of ovipositional preference signals in sorghumpanicles, pearl millet leaves and pearl millet stems.Factors responsible for the ovipositional behavior ofthe pearl millet head miner have not been studied indepth. Generally, it is understood that there is a complexinteraction between insects and their host plants thatgoverns host finding for feeding, mating and oviposition(Brattsen and Ahmad 1986, Metcalf and Metcalf 1992,Hirano et al. 1994, Owusu et al. 1996). Significantovipositional preference for immature pearl millet paniclessuggests the presence of plant chemicals that stimulateoviposition, which are most attractive at 30% panicleextension and decline with panicle age.We have observed in the field that on a night with amoderate breeze, more females invade millet fields thanduring a night of still air (especially after rain) or verystrong wind. These observations suggest that anemotaxismay compliment spectral reflectance and millet paniclevolatiles and serve in combination as the agentsresponsible for host finding, while contact chemoreceptioncombined with plant nutrient composition may beresponsible for discriminative probing and ovipositionsite searching behavior. After landing on millet panicles,females can spend 15–20 minutes probing with theovipositor before oviposition. In some cases, they fly toother panicles after long periods of probing withoutlaying eggs. This behavior remains unexplained; however,we suspect deposition of chemicals by females afteroviposition, which may deter other females from ovipositingon the same panicle.RererencesBernardi M, Mishoe JW and Jones JW. 1989. Raghuva: Acomputer simulation of Raghuva albipunctella populationdynamics and Pennisetum americanum and P. typhoidesphenology. Ecological Modelling 44:275–298.Brattsen LB and Ahmad S. (eds.) 1986. Molecular aspects ofinsect-plant associations. New York, USA: Plenum Press. 346 pp.Hirano C, Yasumi K, Itoh E, Kim C-S and Horiike M. 1994.A feeding deterrent for Thrips palmi Karny (Thysanoptera:Thripidae) found in tomato leaves: isolation and identification.Japanese Journal of Applied Entomology and Zoology38:109–120.Metcalf RL and Metcalf ER. 1992. Plant kairomones in insectecology and control. London, UK: Chapman and Hall. 168 pp.Nwanze KF and Harris KM. 1992. Insect pests of pearl milletin West Africa. Review of Agricultural Entomology 80:1133–1155.Owusu EO, Kim C-S, Horiike M and Hirano C. 1996.Comparative biological and enzymatic studies on some host-adapted populations of melon and cotton aphid, Aphis gossypii(Homoptera: Aphididae). Journal of Agricultural Science,Cambridge 126:449–453.

Observations on factors affecting attraction and oviposition preferences of the millet head miner Heliocheilus albipunctella to pearl millet panicles

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Observations on factors affecting attraction and oviposition preferences of the millet head miner Heliocheilus albipunctella to pearl millet panicles

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