Studies On Some Corn Borers Parasitoids:

George Helmy Ebaid

SUMMARYLaboratory studies were conducted to find out the efficacy of Delfin (ahioinsecticide derived [Tom Bacillus thuringiensi« var. kurstaki) onthe first instar larvae of Sesamia cretlca and the second instar larvae ofOstrinia nubilalls, and also the inspect. ofConsuJt (an1.G.R.) on thefirst instal latvae of S. cretlca. Laboratory studies were also oriented toConomorium sp., which was first recorded in Egypt as pupalendoparasitoid on S. eretica. On the other hand, field included surveyof paJasitoids on immature stage of S. cretica and O. nubilalis and thepercentages of parasitism on pests infesting summer and 1 iliplantations in addition to assaying different control methods against thetwo mentioned pests. The obtained results may be summarized asfollows:Laboratory studies:1-1- Effect of bioinsecticide (Delfin) on Ostrinia nubllalls andSesamia cretica.The efficacy of Delfin (a commercial product of Bacillusthuringiensis) on the 2nd instar larvae of O. nubilalis and 15t instarlai ae of S. eretiea were studied. After 48 hours [rom treatment, theLC50 values were 10 104 S.U. on O. nubilalls and 5.2 x 104 S.U. on S.cretlca. A negative relationship was determined bet een the appliedconcentration of Del fin and LTso’ value i.e. the LT5G was shortened bJthe increase of Delfin concentration in both of O. nubllalis and •.’.cretica. In addition these values were shorter in case of I~1instar larvaeof S. cretica than those of the 2nd instar larvae of o. nubilalis at thesame concentration of Delfin.SUlllmarv- IM,-1-2- ElTect or I.G.R. (Consult) on S. creticaThe lsf instar larvae S. cretica were fed on fresh succulent rolledleaves of maize plants dipped in different concentrations of Consult.The Leso value was 72 p.p.m., 24 hours after treatment. The LT50 wasshortened by increase in Consult concentration.1-3- Morphological studies on Conomorium sp,This study included the first record of Conomorium sp. on S. creticapupae. This parasitoid was identified by Dr. Hannes Baur, staffmember Natural History Museum (Bern, Switzerland).1-3-a-The different immature stages of Conomorium sp, (egg, 4 larvalinstars, prepupa and pupa) were briefly described.Egg of hymenopterous type, on deposition it measures 0.7-mm. longand 0.28 mm. at its widest part. The size of egg increased asdevelopment proceeds to reach 1.31-mm in length and 0.437 mm inwidth, just before hatching. The larva could be easily discerned throughthe transparent chorion. The larva molts three times during itsdevelopment, i.e. it develops through four larval instars.The 151 instar larva is 1.4 mm long and 0.525 mm wide, the body 13segmented. The head capsule measured 0.21O-mm length and its width0.210-mm. Each of the mandibles of 0.14 nun length and 0.070 mmwidth. The 2nd instar measures 2.625-mm in length and 0.7 mm inwidth. Head length and width measured 0.245 and 0.42 mm.Mandibles are O.175-mm long and 0.1OS-mm width. The 3rd instarmeasures 4.2-mm long and 0.875-mm wide. The head capsule is 0.21mm long and 0.315 nun wide. The mandibles are larger in size andlIIHl1l:Jrvmore pigmented than in the preceding stage. Each mandible has broodrounded base and tapers to a sharp end. It measures 0.21mm in lengthand O.14mm at its base. The 4th larval instar measures 3.325mm longand 0.857 mm wide. The head capsule is 0.179 mm in length and 0.208mm at its widest part.Prepupal stage is formed inside the host pupa and measured 2.9-mmin length and 1.0 rum width. The posterior parts of prepupa lackssegmentation. Prepupa transfers to a free type pupa.”which is about 3-nun long and 2.2-mm wide. At the beginning of this stage, the pupa iscreamy in colour, the compound eyes and ocelli appear red. Asdevelopment proceeds, the body darkens gradually starting with thehead and thorax, which become black. Legs appear brown with yellowin some parts.1-3-b- The average duration’s of the egg, the four larval instars, theprepupa and pupa occupied 1.75 ± 0.25,2.25 ± 0.25,3.5 ± 0.09 3.75 ±0.20 4 ±O.18, 1.13 ± 0.12 and 8.5 ± 0.23 days respectively at 25°Cand 65 ± 5 % R.H. The total larval period occupied 13.5 ± 0.72 daysand the total developmental period was 24.88 ± 1.32 days.1-3-c- Emergence of parasitoid adults occurs from one or two holes ofa circular shape and 1- 1.5-null diameter. Emergencies is finishedwithin few hours.1-3-d- Sexes could be easily differentiated by the close e amination ofantenna and genitalia. The antenna is of geniculate type and consists oflong scape, a shorter pedical and a 7-segmented flagellum in bothsexes. The flagella are longer in male (1.22mm) than female (1.05mm).Male has also a pale yellow ring, on the ventral side of abdomen, whichis not present in female.Summar”- I (,X -1-3-e- .hlling occurs immediately just after emergence. Males wereable to male al any lime