Studies on the effects of juvenile hormone analogues on the development of Spodoptera mauritia (Boisduval) (Lepidoptera : Noctuidae)

Abstract

Morphogenetic effects of two juvenile hormone analogues viz. altosid and farnesyl methyl ether (FME) on spodoptera mauritia were studied under laboratory conditions. Ovicidal action was first tested by using different concentrations of juvenile hormone analogues diluted in pure acetone. All the treatments and control (acetone treatment) prevented embryonic development to varying degrees. Since the solvent also caused mortality in eggs, one per cent acetone solution in water was used in later experiments. Treatments ranging from 0.0125 to 0.1 per cent altosid resulted in egg mortality ranging between 40 to 60 per cent . The corresponding mortality figures caused by FME were 36 and 52 per cent, the values were comparatively less than those with altosid.

Freshly moulted last larval instar was the most susceptyible stage to the action of JHA’s. All the hormonal concentrations used in the study affected normal metamorphosis and moulting. Some of the treated larvae moulted into supernumerary larval instars and larval pupal mosaid. Prolonged larval duration, failure of normal moulting altered body pigmentation, reduction in water content of the excreta and slight swelling of the thoracic legs and prolegs were also recorded as hormonal effects on the last instar larvae. Higher dosages of FME had direct toxicity to the larvae. Pupae were more susceptible to the action of altosid than of FME. Metamorphosis was completely inhibited at all doses used. All the treated pupae showed darker colouration than control pupae.

Altosid and FME had effects on fecundity, embryogenesis and latent effect on post embryonic development when the female moths were treated. Reduction of fecundity upto 36 per cent was recorded by 10 µg per µl of both the hormonal analogues used in the experiment. A sizable number of eggs failed to hatch since the embryonic larval differentiation was seriously affected. The progeny of the treated females suffered heavy latent mortality especially in the first larval instar stage. The average adult longevity of the treated moths increased significantly. There was only a marginal increase in the time for laying the first batch of eggs in treated moths. In general altosid was found to be superior to FME in producing morphogenetic effects on spodoptera mauritia.