Abstract
Plants produce chemical defense compounds to resist herbivore attack either by repelling the herbivores or attracting natural enemies of the herbivores. We have previously shown that volatile compounds from cotton released in response to herbivory by conspecifics reduce oviposition in cotton leafworm moth Spodoptera littoralis. It remained, however, unclear whether herbivore-induced changes also affect moth pre-mating and mating behaviours. In this study we examined the effect of herbivore-induced changes in cotton on reproductive behaviours i.e., female calling, male attraction and investment, and mating behaviour in S. littoralis. We found a reduction in the number of females calling i.e., females releasing pheromone, in the presence of cotton plants damaged by larvae of S. littoralis compared to undamaged plants. Females also spent significantly less time calling and showed a delay in calling in the presence of damaged plants. Furthermore, males exhibited significantly delayed activation and reduced attraction towards female sex pheromone in the presence of damaged plants. We also found that mating success and the number of matings were significantly reduced in the presence of damaged plants whereas male investment i.e., spermatophore weight, was not affected. Thus, our study provides evidence that herbivory by conspecifics on host plants affect pre-mating and mating behaviours in an insect herbivore.
Highlights
In phytophagous insects, plant cues are crucial for finding a suitable plant for feeding and oviposition (Bruce, 2015)
During four nights of calling, females exhibited a delay in calling during the first (χ 2 = 9.86, df = 1, P < 0.01), second (χ 2 = 8.73, df = 1, P < 0.01) and third (χ 2 = 5.64, df = 1, P < 0.05), and fourth night (χ 2 = 4.28, df = 1, P < 0.05) in the presence of damaged cotton plants, whereas the females kept with undamaged cotton plants commenced calling much earlier in the scotophase and the overall delay in calling under damaged conditions was significant (χ 2 = 29.46, df = 1, P < 0.001, Figure 3)
No differences in mating duration were observed on an average of (χ 2 = 0.79, df = 1, P > 0.05) or at any of the specific ages tested (1-d-old males: χ 2 = 0.53, df = 1, P > 0.05; 2-d-old males: χ 2 = 0.75, df = 1, P > 0.05; 3-d-old males: χ 2 = 0.58, df = 1, P > 0.05; 4-d-old males: χ2 = 0.67, df = 1, P > 0.05) among the pairs mated in the presence of either damaged or undamaged plants (Figure 7)
Summary
Plant cues are crucial for finding a suitable plant for feeding and oviposition (Bruce, 2015). Synthesis, and production of Herbivory Influence Reproductive Behaviors sex pheromones in females is initiated and enhanced in the presence of host plants suitable for feeding, mating, and oviposition (Raina et al, 1992; Groot and Visser, 2001) whereas non-host plants may produce inverse effects (Zhang and Schlyter, 2004; Sadek and Anderson, 2007). This shows that plant quality as food for the progeny can be important for female calling and attraction of males. Compounds from host plants have been shown to enhance the attraction of males toward female sex pheromones (Landolt and Phillips, 1997; Schmera and Guerin, 2012)
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