Sublethal concentrations of azadirachtin affect food intake, conversion efficiency and feeding behaviour of Spodoptera littoralis (Lepidoptera: Noctuidae)

Abstract

Sublethal concentrations of azadirachtin incorporated into artificial diet and offered to third-instar larvae of Spodoptera littoralis (Boisduval) prolonged larval instars and reduced food intake. These effects were observed after the treated larvae had been transferred to plain diet; the reduced food intake was therefore a secondary antifeedant effect. Azadirachtin did not influence digestion efficiency but diminished the ability of the larvae to convert both ingested and digested nutrients into growth, particularly immediately after treatment. This effect declined with time once the treatment with azadirachtin had ceased. Growth was more severely reduced than food intake, and the reduction in growth also occurred during periods when food intake was not affected, possibly due to post-ingestive effects.

Growth disruption, abnormalities and mortality of Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae) caused by Azadirachtin

“…The results could not be attributed to different rates of food intake, since S. littoralis is able to eat 11.8 times its weight per day during the 4 th larval instar and only 2.5 times during the last instar (Martinez & van Emden 1999). Therefore, larvae treated at the 3 rd larval instar would have ingested higher amounts of azadirachtin per body weight than those at the last instar.…”

“…1). Likewise Nicol et al (1995), who tested the effect of neem-oil sprays on 3 rd -instar to the reduction of food intake and to the hability of converting food into biomass, reported for S. littoralis (Martinez & van Emden 1999). MRGR could not be evaluated for 0.5 ppm and 1 ppm azadirachtin after treatment because 100% of the insects were killed during the period.…”

The effect of sub-lethal doses of Azadirachta indica (Meliaceae) oil on the midgut of Spodoptera frugiperda (Lepidoptera, Noctuidae)

“…Martinez & Van Emden (1999) reported the prolongation of the larval stage and feeding reduction caused by azadirachtin at sub-lethal concentrations when incorporated in artificial diets offered to 3 rd instar caterpillars of Spodoptera littoralis (Boisduval). The authors describe this secondary effect because of reduced food ingestion or due to the presence of inhibitors in the food or even due to inadequate feeding.…”

Sublethal Effects of Spinosad (Tracer®) on the Cotton Leafworm (Lepidoptera: Noctuidae)

“…The reductions in food intake and in the ability to convert food into biomass would eventually have extended the development time of the larvae. The effects on the nutritional responses of S. littoralis were more pronounced in the instars immediately after the treatment, than later when a recovery of normal behavior occurred (Martinez and van Emden 1999). Thus, besides the lack of adequate food intake and impaired metabolism following spinosad treatment, it is possible that sublethal concentrations fed to S. littoralis affected the endocrinal events to a small extent manifested by delays in insect development.…”

“…Nasiruddin and Mordue (1993) reported the adverse effects of azadirachtin on midgut epithelial cells, which might disrupt enzyme secretion and nutrient absorption. The ability to convert food into biomass was reduced after third instar S. littoralis larvae were fed on diet treated with azadirachtin for two days, and this could have affected growth (Martinez and van Emden 1999). Timmins and Reynolds (1992) attributed a similar reduction in the efficiency of food utilization following Manduca sexta treatment with azadirachtin to increased energetic costs arising from a reduced ability to utilize dietary nitrogen, which would not necessarily interfere with absorption from the gut (digestibility).…”