Impact of UV radiation on activity of linear furanocoumarins andBacillus thuringiensis var.Kurstaki againstSpodoptera exigua: Implications for tritrophic interactions

Abstract

Acidic fogs with a pH of 2.0 and duration of 2 hr did not reduce the efficacy ofBacillus thuringiensis var.Kurstaki (Berliner). Therefore, the impact of UV radiation was investigated on the interactions between (1) levels of the antibacterial linear furanocoumarins psoralen, bergapten, and xanthotoxin inApium graveolens (L.) occurring following a 2.0 pH acidic fog episode, (2) the noctuidSpodoptera exigua (Hübner), and (3) a sublethal dosage of the microbial pathogenB. thuringiensis var.Kurstaki. Mean time to pupation in the absence of UV radiation (survival was too low to conduct this analysis for insects exposed to UV) was significantly extended by the addition of either psoralens orB. thuringiensis. Larvae developing on diets containingB. thuringiensis plus psoralens required nearly 40% longer to pupate than controls, but their effects were additive as the interaction was not significant. Although the mean times to adult emergence were significantly different, time spent in the pupal stage did not vary significantly between treatments, indicating that increases in larval developmental time were responsible for the observed decrease in developmental rate. Mean time to mortality, a weighted average time of death, was not significantly affected by any of the treatments. In a 2 × 2 × 2 factorial analysis, all main effects (linear furanocoumarins.B. thuringiensis, UV radiation) reduced survival significantly, as did the three-way interaction. Thus, antagonistic interactions with psoralens that would reduce the effectiveness ofB. thuringiensis in the field were not observed. When pairs of main effects were nested within the two levels (presence and absence) of the third factor, several two-way interactions were found. Interestingly, the activity ofB. thuringiensis and the psoralens, individually or in combination, was enhanced by exposure to UV radiation. Implications of this research are discussed for both natural and agricultural ecosystems.

Susceptibility of Tuta absoluta (Meyrick) (Lep., Gelechiidae) reared on two species of Lycopersicon to Bacillus thuringiensis var. kurstaki

“…Plant resistance factors are known to increase the activity of alpha‐endotoxin on insects. Several authors have also observed insect effects of plant resistance factors, increasing the insect susceptibility to B. thuringiensis (K EA et al., 1978; S HULTZ , 1983; F ELTON and D AHLMAN , 1984; B REWER and A NDERSON , 1990; T RUMBLE et al., 1991; S IVAMANI et al., 1992). Spore viability and persistence of B. thuringiensis can also be influenced by plant resistance factors.…”

Effect of CryIC toxin from Bacillus thuringiensis on larval feeding behavior of Spodoptera exigua

“…in several IPM programs (Trumble, 1990;Trumble et al, 1994), suggesting that these data would have practical application in commercial agriculture. Considerable information is also available on interactions between the plant hosts, B.t., and S. exigua (Trumble et al, 1991;Meade & Hare, 1994). Finally, several behavioral responses to food sources have been described for this insect (Berdegu6 & Trumble, 1996).…”

Furocoumarins in Medicinal Chemistry. Synthesis, Natural Occurrence and Biological Activity

“…Furthermore, evidence for molluscicidal [196], insecticidal [197] and insect antifeedant activity [198] has been found for bergapten and other linear furocoumarin analogs. Antibacterial activity was also found in certain psoralens [199] and 4',5'-dihydropsoralens [185]. Anti-HIV activity was described in various furocoumarins such as TMP [200] and natural analogs recently isolated from Prangos tschimganica [120].…”