Effect of avocadofurans on larval survival, growth, and food preference of the generalist herbivore, Spodoptera exigua

Abstract

We examined the effect of two avocadofurans, 2‐(pentadecyl)furan and 2‐(heptadecyl)furan, from avocado idioblast oil cells on maturation and larval feeding behavior of a generalist insect herbivore, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae). Experiments were conducted using two larval sizes: early‐stadium larvae refer to those larvae from experiments initiated with neonates while late‐stadium larvae refer to those larvae from experiments initiated with third instars. In order to use selected sublethal doses for developmental and behavioral studies on early‐ and late‐stadium larvae, log‐dose probit lines were determined using diet incorporation bioassays. Both avocadofurans had similar toxicities to early‐stadium larvae [LC50= 2.2 and 1.9 μmoles/g of diet for 2‐(pentadecyl)furan and 2‐(heptadecyl)furan, respectively] and late‐stadium larvae (LC50= 3.0 and 3.4 μmoles/g of diet, respectively). In diet bioassays extending from egg hatch to adult emergence, the avocadofurans significantly prolonged larval developmental times and reduced S. exigua pupal weights. In 7 d no‐choice bioassays initiated with cohorts of newly‐molted third instars, the avocadofurans significantly reduced larval weights at various sublethal concentrations (below LC50 values). To test larval feeding deterrence effects of these avocadofurans, choice tests were conducted using early and older instar larvae. A significantly higher proportion of early‐stadium larvae preferred control diet over diet treated with either avocadofuran at several sublethal concentrations. Similarly, choice tests with late‐stadium larvae showed greater proportions of larvae on control diet than treated diet even at concentrations below the LC50. Moreover, late‐stadium larvae consumed significantly more of the control diet than the treated diet. Thus, the avocadofurans may act as feeding deterrents as well as toxicants in plant protection against non‐adapted insect herbivores.

Phenotypic Variations in the Foliar Chemical Profile of Persea americana Mill. cv. Hass

“…The 2‐[(8 Z ,11 Z )‐heptadeca‐8,11‐dienyl]furan reduces larval growth of B. mori . The avocadofurans have insecticide and feeding deterrent activity against non‐adapted herbivorous insects such as S. exigua . Squalene is reported as attractant for parasitoids and predators of apple insect pests .…”

Antifeedant activity and toxicity of leaf extracts from Porteresia coarctata Takeoka and their effects on the physiology of Spodoptera litura (F.)

“…While plant metabolites may produce toxic eVects when ingested by insects, antifeeding activity may determine the extent of insect herbivory. Several papers have been published on the entomotoxic properties of crude extracts from diVerent plant species (Sadek 1997(Sadek , 2003Rodriguez-Saona and Trumble 1999;Ciccia et al 2000;Tapondjou et al 2005). However, utilization of many phytochemicals as botanical insecticides and/or antifeedants is still at an early stage of development.…”

Secretory avocado idioblast oil cells: evidence of their defensive role against a non‐adapted insect herbivore

“…Our previous studies identified various compounds in the avocado idioblast oil, including persin and several alkylfurans, which are responsible for the toxicity and antifeedant effects observed for S. exigua (Rodriguez-Saona et al, 1997, 1998Rodriguez-Saona & Trumble, 1999). In this study, we provide the first experimental evidence that idioblast oil cells can serve a defensive function in deterring non-adapted herbivores.…”

“…However, Kobiler et al (1993) also indicated that intact idioblast cells in the fruit mesocarp were not toxic to C. gloeosporioides, and proposed that the cell thickness blocks contact with fungal hyphae. The 2-alkylfurans were reported to cause toxic (Rodriguez-Saona et al, 1998) and feeding deterrent effects (Rodriguez-Saona & Trumble, 1999) on the non-adapted S. exigua larvae. Similarly, oil extracted from idioblast cells was toxic to the beet armyworm, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) (Rodriguez-Saona & Trumble, 1996).…”

“…More recently, a group of 2-alkylfurans were identified from a second active fraction obtained after fractionationation of the crude oil (Rodriguez-Saona et al, 1998). The 2-alkylfurans were reported to cause toxic (Rodriguez-Saona et al, 1998) and feeding deterrent effects (Rodriguez-Saona & Trumble, 1999) on the non-adapted S. exigua larvae.…”