The biological control of Sunn Pest, Eurygaster integriceps Put. (Het.: Scutelleridae) using egg parasitoids

Scelionid wasps, the Sunn pest egg parasitoids, are considered one of the most important regulation factors of Eurygaster integriceps population in wheat. A faunistic study during 2004-2006 demonstrated that there were 3 species viz. Trissolcus grandis, T. semistriatus and T. vassilievi parasitizing the Sunn pest eggs in all provinces studied. However, a 4th species, T. basalis, was recorded on the pest only in Tehran province. Investigations on some prominent biological attributes proved significant differences among the wasp species and populations. In this way, T. grandis populations differed significantly with other species and populations showing the shortest immature developmental time. Although, immature survival rate and adult longevity were not significantly different among species and populations in general, T. grandis population of Esfehan had significantly the lowest immature survival rate compared with that of other populations. Similarly, the female fecundity differed significantly across species and populations. However, the egg laying span showed similar pattern among species and populations. Totally, the data could not determine a unified and vivid relationship between the fecundity and the egg laying duration at all. In addition, the gross and net reproductive (GRR and NRR) rate were significantly different among the populations, therefore, Lortestan and Tehran population of T. vassilievi with 240. 807 and 227. 505 eggs, respectively, had the highest NRR compared with that of other species and populations. Considering the mentioned characteristic, the maximum NRR was estimated for Tehran population of T. vassilievi which was as high as 2. 5 times compared with that of other populations. Besides, the highest amount of intrinsic and finite rate of increase was obtained for the populations of T. grandis, T. semistriatus and T. vassilievi of Golestan, West Azarbaijan and Tehran, respectively. Later on, the shortest generation time was calculated for Golestan population of T. grandis as 13. 643 days. The findings on the physical conditions cleared that all the studied species were able to complete their growth and development in tested temperature treatments. However, there were significant effects of temperature on the immature developmental time and survival rate, adult (male and female) longevity, realized fecundity and progeny sex ratio of species and populations. Pooling up all data, it could be concluded that the treatment of 25±1 ºC and 60±5% RH was relatively the most optimized environmental conditions for rearing studied species. Another very important achievement of the current research revolved around the subject of Sunn pest parasitoids' mass production. It had already been concreted that E. integriceps and Graphosoma lineatum could be reared as the natural hosts for the mass production of the Sunn pest parasitoids; yet, it was illustrated that the proper ratio of the host (eggs) to the female parasitoids in the mass production systems should receive more attention. Besides, the time of substitution of old colonies with the fresh ones was recognized very critical in the mass production of the Sunn pest's natural enemies. The demographic approach revealed that two host egg masses (~28 eggs) /female/day was the optimum ratio. Finally, the most economical time for removal of old colonies and establishment of new ones was recorded as 10 days after parasitoid females' emergence. A detailed discussion on the theoretical and practical application of the results has been presented.