FECUNDITY AND EGG DISTRIBUTION OF THE HERBIVORE SPODOPTERA-PECTINICORNIS AS INFLUENCED BY QUALITY OF THE FLOATING AQUATIC PLANT PISTIA-STRATIOTES

We determined the influence of host quality of the floating aquatic we ed Pistia stratiotes L. (Araceae) on the fecundity and egg distributio n of the biological control agent Spodoptera pectinicornis (Hampson) ( Lepidoptera: Noctuidae). Different nutritional levels were produced by growing plants with relatively low and high levels of nitrogen, phosp horus and potassium fertilizer. Female and male pupal biomass were sig nificantly greater when the larvae were fed leaves from the high ferti lizer plants. Although the fertilizer treatments did not significantly influence total fecundity, there was an indirect effect as adults fro m larger pupae were more fecund. Regardless nf treatment ovipositing f emales, formed a depression in the leaf surface by removing trichomes into which they deposited the egg masses. Most of the egg masses were laid on the lower leaf surface, on leaf positions 5-8 (counting from t he young inner to the outer leaves) and during days 1-2 post-eclosion. Most of the eggs were laid in masses but about 12% were solitary. Fem ales fed the low fertilizer treatment laid a greater proportion (mean +/- s.e.) of their eggs as solitary eggs (17.3 +/- 3.4% of total eggs) than did females fed the high fertilizer treatment (8.3 +/- 2.3% of t otal eggs). The increased percentage of solitary eggs laid by the fema les from the low quality larval diet may be an adaptive response to de crease competition among the progeny.