Bt rice plants may protect neighbouring non- Bt rice plants against the striped stem borer, Chilo suppressalis

Abstract

The area planted with insect-resistant genetically engineered crops expressing Bacillus thuringiensis (Bt) genes has greatly increased in many areas of the world. Given the nearby presence of non-Bt crops (including those planted as refuges) and non-crop habitats, pests targeted by the Bt trait have a choice between Bt and non-Bt crops or weeds, and their host preference may greatly affect insect management and management of pest resistance to Bt proteins. In this study, we examined the oviposition preference of the target pest of Bt rice, Chilo suppressalis, for Bt versus non-Bt rice plants as influenced by previous damage caused by C. suppressalis larvae. The results showed that C. suppressalis females had no oviposition preference for undamaged Bt or non-Bt plants but were repelled by conspecific-damaged plants whether Bt or non-Bt. Consequently, C. suppressalis egg masses were more numerous on Bt plants than on neighbouring non-Bt plants both in greenhouse and in field experiments due to the significantly greater caterpillar damage on non-Bt plants. We also found evidence of poorer performance of C. suppressalis larvae on conspecific-damaged rice plants when compared with undamaged plants. GC-MS analyses showed that larval damage induced the release of volatiles that repelled mated C. suppressalis females in wind tunnel experiments. These findings suggest that Bt rice could act as a dead-end trap crop for C. suppressalis and thereby protect adjacent non-Bt rice plants. The results also indicate that the oviposition behaviour of target pest females should be considered in the development of Bt resistance management strategies.

Caterpillar-induced rice volatiles provide enemy-free space for the offspring of the brown planthopper

“…To infest plants with SSB caterpillars, two 3 rd instar caterpillars were starved for at least 3 hr and then placed on a wild or cultivated rice plant. The rice stems infested with caterpillars were covered with plastic sleeves to prevent insects from escaping ( Jiao et al, 2018 ). Within 24 hr, the caterpillars drilled into the stems and caused visible damage to the plants.…”

“…Volatiles emitted by rice plants were collected using a dynamic headspace collection system as described by Jiao et al, 2018 . Ten plants were transferred into a glass bottle (3142 ml).…”

“…Air was filtered through activated charcoal, molecular sieves (5 Å, beads, 8–12 mesh, Sigma-Aldrich), and silica gel Rubin (cobalt-free drying agent, Sigma-Aldrich) before entering the glass bottles. The system was purged for 30 min at 400 ml/min with purified air before attaching a tube filled with 30 mg Super Q traps (80/100 mesh, ANPEL Laboratory Technologies (Shanghai) lnc, China) to the air outlet in the lid to trap the headspace volatiles ( Jiao et al, 2018 ). Volatile collection lasted for 4 hr (11:00-15:00) in a climate chamber at 27 ± 3°C, 75 ± 10% RH.…”

“…Volatile compounds were identified by mass spectral matches to library spectra as well as by matching observed retention time with that of available authentic standards. If standards were unavailable, tentative identifications were made based on referenced mass-spectra available from NIST (Scientific Instrument Services, Inc, Ringoes, NJ, USA) or based on a previous study ( Xiao et al, 2012 ; Jiao et al, 2018 ). Relative quantifications of compounds were first based on their integrated areas related to the internal standard ( De Lange et al, 2020 ).…”

“…For instance, HIPVs serve as cues for natural enemies, such as predators and parasitoids, to locate their prey or hosts ( Dicke et al, 2009 ; Allison and Daniel Hare, 2009 ; Allmann and Baldwin, 2010 ; Halitschke et al, 2008 ; Turlings and Erb, 2018 ; Schuman and Baldwin, 2018 ; Joo et al, 2018 ). They also play a role in repelling herbivores that avoid inducible plant defenses and conspecific or heterospecific competition ( De Moraes et al, 2001 ; Knolhoff and Heckel, 2014 ; Anderson et al, 2011 ; Jiao et al, 2018 ) or they can attract specialist herbivores that aggregate to collectively overcome the defense of their hosts ( Loughrin et al, 1995 ; Weed, 2010 ; Robert et al, 2012 ). HIPVs can also be detected by neighboring plants and help them to anticipate an incoming attack ( Arimura et al, 2000 ; Heil and Ton, 2008 ; Engelberth et al, 2004 ; Karban et al, 2014 ; Sugimoto et al, 2014 ; Nagashima et al, 2018 ).…”