Bianca G. Ambrogi

Current knowledge and future research perspectives on cassava (Manihot esculenta Crantz) chemical defenses: An agroecological view

Cassava (Manihot esculenta Crantz) is one of the most important staple crops worldwide. It constitutes the major source of carbohydrates for millions of low-income people living in rural areas, as well as a cash crop for smallholders in tropical and sub-tropical regions. The Food and Agriculture Organization of the United Nations predicts that cassava plantations will increase and production systems will intensify in the future, highlighting the need for developing strategies that improve the sustainability of production. Plant chemical defenses hold the potential for developing pest management strategies, as these plant traits can influence the behavior and performance of both pests and beneficial arthropods. Cassava plants are well-defended and produce a number of compounds involved in direct defense, such as cyanogenic glycosides, flavonoid glycosides, and hydroxycoumarins. In addition, volatile organic compounds induced upon herbivory and the secretion of extrafloral nectar act as indirect defense against herbivores by recruiting natural enemies. Here, cassava chemical defenses against pest arthropods are reviewed, with the aim of identifying gaps in our knowledge and areas of research that deserve further investigation for developing sound pest control strategies to improve sustainable production of this crop, and how these defenses can be used to benefit other crops. Cyanogenic content in cassava is also highly toxic to humans, and can cause irreversible health problems even at sub-lethal doses when consumed over prolonged periods. Therefore, the promotion of chemical defense in this crop should not aggravate these problems, and must be accompanied with the education on processing methods that reduce human exposure to cyanide.

Trail‐following behaviour and biological aspects of the gregarious caterpillar Brassolis sophorae (Lepidoptera: Nymphalidae)

Brassolis sophorae (Linnaeus), the coconut palm caterpillar, is a pest in the Northeast region of Brazil. Despite its great importance, information about the biology and behaviour of this insect is scarce. B. sophorae caterpillars are gregarious, and they remain in a nest during the daytime and only come out at dusk to feed. When caterpillars leave the nest to forage, they lay down a trail of silk that leads the group to the feeding site. In spite of this, there is no scientific evidence showing whether trail‐following behaviour in B. sophorae caterpillars is mediated by silk‐associated chemical cues. This gregarious behaviour has probably hampered biological studies of this species. We determined biological parameters (number of instars and development time of each instar) of the larvae and conducted behavioural assays to assess whether trail‐following behaviour of B. sophorae is mediated by chemical (silk extract) or physical (solvent‐washed silk) cues, or a combination of both. Measurements of the head capsule width showed that B. sophorae larvae pass through six instars in an average period of 12 days per instar. Dual‐choice tests in a Y‐shaped arena showed that the larvae significantly preferred to walk on a silk‐covered surface over a clean one and on a silk extract over hexane alone. When caterpillars were given the choice of walking on silk or on solvent‐washed silk, they did not show a preference for either treatment. These results demonstrate the presence of pheromonal compounds in the silk of B. sophorae although the communication between caterpillars of B. sophorae is also mediated by physical cues. The results of this study broaden knowledge on the trail‐following behaviour of immature larvae as well as the biology, morphology and behaviour of this insect.