Biological activity of two juvenoids and two ecdysteroids against three stored product insects

The insecticidal activity of juvenile hormone agonists methoprene and pyrip roxyfen, and the ecdysone agonists RH-5849 and tebufenozide was evaluated a gainst susceptible and actellic-resistant strains of Tribolium castaneum an d susceptible strains of Rhyzopertha dominica and Sitophilus oryzae. Concen trations ranging from 0.1 to 20 ppm of the analogues were mixed in the food medium to which the tested insects were exposed. The results showed that a ll these compounds could affect the development of the tested species to di ffering extents but had no effect on the mortality of parental adults. The two JH analogues did not prolong the life span of R. dominica and S, oryzae , but very greatly extended that of T. castaneum. The extension led to the production of giant larvae and failure to pupate. Actellic-resistant strain of T. castaneum showed some cross-resistance to methoprene and pyriproxyfe n, but not to RH-5849 and tebufenozide. Pyriproxyfen was the most effective compound among the four IGRs; a concentration of 0.1 ppm could completely inhibit the F-1 adult occurrence of both S- and R-strains of T. castaneum a nd its LC(90)s for controlling R. dominica and S. oryzae were 0.1 and 1.2 p pm, respectively. Methoprene was highly effective against R. dominica, but less active on S, oryzae. RH-5849 could achieve almost complete control of F-1 adults of T. castaneum and R. dominica at 10 ppm, but was less potent o n S. oryzae. Tebufenozide appeared to be much less active on these three sp ecies compared with the other three compounds. The percentage reductions of F-1 adults for S- and R-strains of T. castaneum at a concentration of 20 p pm were 80 and 99%, respectively. (C) 2000 Elsevier Science Ltd. All rights reserved.