Spodoptera litura (F.) (Lepidoptera: Noctuidae) is a serious pest of several crops in India and other countries. Prothoracicotropic hormone (PTTH) release from the brain of penultimate fifth instars of the noctuid was followed in the laboratory and a spiracle index developed to assess PTTH action. PTTH release from the brain occurred during the scotophase at 4.30 h of day 1 (AZT). Ecdysone secreted in the prothoracic gland was released from the 7th hour of day 1 (AZT), reaching a maximum in the haemolymph on the 9th hour of day 1 (AZT). The prothoracic gland showed three distinct phases, namely growth, synthesis and release. Injected PTTH of 5th instar brain extract induced larval moulting in head-ligated larvae. Partially purified PTTH from 6th-instar S. litura brain induced moulting in 6th instars. Abdomen-ligated penultimate instars administered β-ecdysone showed variable moulting response. The phenomenon of hormonal interaction with development of the penultimate instar of S. litura is discussed.

Culex quinquefasciatus (Wiedemann) mosquitoes, which are refractory to Brugia pahangi (Buckley and Edeson) microfilariae, were fed simultaneously on Wuchereria bancrofti (Cobbold) and B. pahangi microfilariae. A selected stock of Aedes aegypti (L) which is susceptible to both of these filariae was used as a control. The exsheathment and migration rates of B. pahangi in C. quinquefasciatus increased significantly as compared to those of B. pahangi when given as a feed by itself. These two processes did not show any trend with time. On dissection, 12 and 14 days postinfection, 27% of C. quinquefasciatus were found to be infected with an average of two larvae per mosquito. Of the total number of larvae found 78% were W. bancrofti while 22% were B. pahangi.

Feeding C. quinquefasciatus on in vitro exsheathed B. pahangi microfilariae suspended in serum did not increase the rate of migration, whereas 71–100% of Ae. aegypti became infected with a mean of 3.5 larvae per mosquito.

Inoculation of C. quinquefasciatus mosquitoes into the thorax and abdomen with exsheathed B. pahangi did not increase their infection rate, whereas in Ae. aegypti 67–82% became infected.