Morphogenetic Aberrations Induced by a Juvenile Hormone Analogue in the Mosquito Culex Tarsalis (Diptera: Culicidae)

The insect growth regulator (IGR) Altosid™ (Isopropyl 11-methoxy-3,7,11-trimethyldodeca-2,4-dienoate) induced a wide range of morphogenetic changes in treated 4th instar Culex tarsalis Coquillett dying after exposure to the IGR. Some pupae at the stage of the larval-pupal intermolt were unable to escape from the larval exoskeleton. The most common site of attachment between larval exuvia and pupal body was in the cephalic region. This resulted in an abnormal constriction in the cephalothoracic area of the pupa. Some adult C. tarsalis resulting from a larval population treated with Altosid were unable to detach legs and wings from the pupal cast-skin, thus dying at this stage. Several other morphogenetic aberrations in pupae and adults dying as a result of exposure of larvae to IGR were also noted. The frequency distribution of the various morphogenetic aberrations occurring in pupae and adults of C. tarsalis resulting from a treated larval population was governed by the concentration of the IGR. No normal dead pupae were found at any of the concentrations used. The number of normal 4th instars dying due to the treatment was also negligible. The majority of the treated population died as pupae exhibiting various degrees of morphogenetic aberrations. Only 2 individuals in the whole treated population were found to exhibit bimorphic forms. One individual was a larval-pupal intergrade and the other a pupal-adult intergrade. The remaining treated C. tarsalis dying, due to the IGR treatment were at various stages of development in a given stadium.