Role of feeding in the reproductive 'group effect' in females of the German cockroach Blattella germanica (L.)

We have found that whether a female German cockroach, Blattella germanica ( L.), is kept alone or in the presence of another female has a major impact on how fast it reproduces and how much it eats. By the sixth day of adultho od, females paired since adult eclosion had substantially larger oocytes th an did females isolated during the same time, and females paired with intac t females, or with ones rendered incapable of feeding, consumed more rat ch ow in the first six days of adulthood than did isolated females. The stimul atory effect of pairing on reproduction was, however, partially independent of feeding because the oocytes of solitary and paired females differed in size on day 6 even when they were given, and had consumed, the same amount of food. This result was confirmed with analysis of covariance using the to tal food intake of a female as the covariate in the analysis. A female's so cial condition probably influenced the development of its oocytes by affect ing the quantity of juvenile hormone synthesized by its corpora allata. The corpora allata of paired females produced more hormone than did those of i solated ones, even when all females had consumed an equivalent amount of fo od, Moreover, females treated with a juvenile hormone analog, fenoxycarb, r eproduced more quickly than identically reared and fed control females, sho wing that juvenile hormone could influence reproduction independently of fe eding. We conclude that both group rearing and food intake accelerate oocyt e development by diminishing the brain's inhibition on the synthesis of juv enile hormone. (C) 2000 Elsevier Science Ltd. All rights reserved.