Quality Control Of Mass-Produced Parasitoids Of The Genus Trichogramma

• Sherif A. Hassan
• Institute for Biological Control, Darmstadt, Germany

Abstract

The efficacy of biological control treatments is dependent on the quality of the natural enemies that are mass-produced by commercial companies. Quality control has always been an important factor in biocontrol. Only if the grower is confident of the method and can trust the product that is delivered he will continue to use it. There are about twenty insectaries in Germany that produce about 60 natural enemies for use in biological control. The reliability of biological control would be considerably improved if producers observed product quality standards. The International Organization for Biological Control (IOBC), Working Group "Quality control of mass reared arthropods" has developed standard methods to measure the quality of mass reared natural enemies, including species of Trichogramma. IOBC has promulgated standards for Trichogramma brassicaeT. Maidis n. sp.) (Hymenoptera: Trichogrammatidae) covering: (1) sex ratio ( 50% females), (2) number of females (as indicated on label), (3) fecundity ( 40 offspring/7 days/female), (4) longevity ( 80% live for 7 days), and (5) parasitism on natural host ( 10 parasitized host eggs/4 hours/female). The quality of the parasitoid is tested regularly at the Institute for Biological Control in Darmstadt. To maintain high quality, the parasitoid is reared at the institute under fluctuating conditions (18 h at 27-28°C, 60-70 % RH and 6 h at 17-18°C, 80-90 % RH). Colonies of the parasite are maintained on both S. cerealella, the usual mass-rearing host and on eggs of the natural host O. nubilalis. The natural host is used at intervals of about 6 months since parasitoid quality can decrease with continuous rearing on eggs of the factitious host. Also, to select for better flight and searching ability on corn plants with natural host eggs, the institute makes releases in greenhouses every year. In addition, the parasites are periodically exposed to both high (32°C) and low (10°C) temperatures. To prevent genetic bottlenecking of the rearing colony, about 10 sub colonies, each with about 10,000 parasites, are maintained permanently to increase the genetic diversity of the parasite in rearing. The quality of commercially produced Trichogramma in Germany was regularly controlled by the Biological Research Center as well as by the plant protection research service. From 1980 to date, samples of T. brassicae are taken directly from the producing companies as well as the growers before treatment. In each releasing device sample, the number of parasitised host eggs found and the performance of the emerging parasitoid are tested. Minimum numbers and qualities are standardized in agreement with the producers. The results of the quality control tests are sent to the companies and to the extension service. A meeting organized by the farmers association in cooperation with the plant protection service is held every year. This includes colleagues from the national research center, producers and distributors. The results of the quality control tests are presented and discussed. Companies not fulfilling the minimum requirements (number of emerged adults, capacity of parasitism) are given the chance to comment and ways to solve emerging problems are established. In this meeting, the results of the field-testing experiments carried out by the plant protection crevice are also dealt with. The quality of the products as seen from the laboratory experiments and the efficacy of the treatments as shown by the field tests are then compared for each case.