Submitted to: Southwest Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 3, 1997
Publication Date: N/A
Interpretive Summary: Biological control will play an important role in the management of cotton insects, especially in the Rio Grande Valley of Texas where many farmers have abandoned pesticides as being ineffective. Trichogramma spp. are the main biological control agents used worldwide. These tiny parasitic wasps attack more than 400 pest species, mostly moth eggs. About 32 million ha of agricultural and forest land are treated with Trichogramma annually. Trichogramma is widely used as a biological control agent in Western and Eastern European countries, Southeast Asia and South America. We tested Trichogramma minutum, which is imported, and T. pretiosum, which occurs naturally in Texas, against beet armyworm under laboratory and field conditions. We found that both parasite species attack and develop on beet armyworm eggs. Results of field experiments demonstrated the ability of Trichogramma spp. to parasitize and puncture significant numbers of host eggs under field conditions. For effective use of these parasites in field integrated pest management (IPM) programs, a systems approach must be developed to optimize rearing and release methods.
Technical Abstract: Studies were conducted to assess the ability of Trichogramma pretiosum Riley and Trichogramma minutum Riley to parasitize eggs of beet armyworm, Spodoptera exigue (Hubner). In the laboratory, beet armyworm egg masses were exposed at a ratio of 1 parasitoid female per host egg for 24 h. Helicoverpa zea (Boddie) eggs were used as a control host. In small field plots, beet armyworm egg masses were exposed at a rate of 5 parasitoid females per host egg for 24 h. The control consisted of egg masses that were not exposed to parasitoids. The laboratory results showed that T. pretiosum parasitized 44.8% of beet armyworm egg compared to 51.6% for T. minutum, 24.9% or 29.3% of the eggs desiccated, respectively, compared with 5.8% in the control group. Certain biological parameters of T. pretiosum and T. minutum reared on beet armyworm were not significantly different than those reared on bollworm eggs (development time, emergence rate, the percentage of females, their body length, and the percentage of deformed females). However, longevity of both parasite species reared on beet armyworm was significantly higher than counterparts reared on bollworm. In small plot experiments, total mortality of beet armyworm (parasitized + desiccated eggs) was 60.9% (36.8% + 24.1%) in plots where T. pretiosum were released, and 53.2% (32.5% + 20.7%) in release sites of T. minutum. These results demonstrate the ability of both parasitoids to attack and develop on beet armyworm eggs and suggest a potential for use in field control effects.