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Abstract
ABSTRACT
Maize (Zea mays L.) is a major cereal crop in Egypt. Sitotroga cerealella is a pre-harvest and post-harvest pest on maize ears and grains. The susceptibility of six commonly grown maize varieties to infestation with this pest was investigated under natural infestation conditions during two successive maize growing seasons. The % grain infestation was determined during three different periods; pre-harvest, sun-drying and storage. For all tested varieties, the % grain infestation during the pre-harvest and sun-drying periods was noticeably low (<2%) while during the storage period it increased from 11 % to 82 %with the progress of the storage period. Accoeding to preference for egg deposition, the percentages of grain infestation and weight-loss refered that SC 10 and SC 124 were the least susceptible, TC 323 was the most susceptible and Cairo 1, Giza 2 and TC 321 were of intermediate susceptibility.
The life-history of S. cerealella on maize grains was studied under constant laboratory conditions of 27 °C and 65±5 % R.H. The egg stage lasted for 3-5 days with 85-100% hatchability. Four larval instars followed by a pre-pupal period were approximated. The 1st, 2nd, 3rd, and 4th larval instars lasted for 4-6, 5-7, 5-6 and 5-7 days, respectively. Pre-pupal and pupal periods lasted for 2-3 and 5-9 days, respectively. Adult longevity ranged 6-8 days for males and 8-14 days for females. The number of eggs per female ranged 164-186 eggs. Pre-oviposition, oviposition and post-oviposition periods elapsed 2 - 3, 3-5 and 3-6 days,respectively.
The sensitivity of newly-laid eggs (< 24 h old), 4th instar larvae and 3-days old pupae to 4 modified atmospheres (MAs) containing 30%, 45%, 65% and 75% CO2 in air was investigated at 3 temperatures of 20, 27 and 34 ?C and exposure periods of 2–288h. The % mortality of the newly-laid eggs as wall as the % reduction of adult emergence from 4th instar larvae and 3- days old pupae tended to increase with the increase of CO2 concentrations in air, increase of temperature and increase of exposure period. According to LT95 values, the descending arrangement of the sensitivity of the 3 tested developmental stages of S. cerealella to the 4 tested MAs under the 3 tested temperatures was as follows: eggs > pupae > larvae. Treatment of dismounted maize grains in airtight containers with a modified atmosphere containing 65% CO2 in air for at least 336 h (two weeks) entirely protected the grains against all of the developmental stages of the pest.