Optimal foraging theory states that an individual should collect and handle food to maximize fitness at lower cost (MacArthur and Pianka 1966; Schoener 1971). Foraging behaviour of individuals can be affected by extrinsic and intrinsic factors. Extrinsic factors include: abundance, seasonality, diversity, spatial distribution, nutritional value of food and predation risks involved with foraging. Intrinsic factors include: health, size, social status within a group, and reproductive or developmental stage of the forager. In several studies it has been reported that males and females exhibit different foraging strategies to maximize their reproductive output (Maklakov et al. 2009; Johns et al. 2010: Nakashima and Hirose 2003). Mating can be energetically costly in both sexes with offspring production constituting the highest energy demand (Andersson 1994). With such high energy demand associated with offspring development, animals are capable of adjusting their dietary preferences to satisfy the optimal nutritional requirements (Tsukamoto et al. 2014). Mating is an integral part of reproduction in all sexually reproducing animals, allowing sperm transfer and egg fertilization. It can be a critical turning point in an animal’s life which causes changes in physiology, behaviour, and gene expression in a wide range of organisms (White et al. 2021; Schwenke et al. 2016).
In insects, postmating physiological changes such as; increased oviposition (Chen 1984), down regulation of female’s immune system (Oku et al. 2019), modulation of release of signalling molecules (Rubinstein and Wolfner 2013; Avila et al. 2011; Lee et al. 2009) which regulates heart muscle contraction (Nichols 2003) and oviduct muscle contraction (Lange 2004), have been extensively studied (Oku et al. 2019; Liu and Hao 2019; Carmel et al. 2016). These changes are more exaggerated in the mated females than the mated males. For instance, female Drosophila melanogaster (Meigen) exhibits post-mating behavioural changes, like ovulation stimulation and decreased courtship receptivity, as a result of an activated immune system (Lawniczak and Begun 2004; McGraw et al. 2004; Peng et al. 2005). Other than Drosophila melanogaster, these changes have also been reported in other insects, such as Ceratitis capitata (Wiedemann) (Jang 2002), Culex pipiens, Linnaeus (Chiba et al. 1992), Helicoverpa armigera Hubner (Jin and Gong 2001) and in Leptocarabus procerulus Chaudoir (Takami et al. 2008).
In most animals including insect responses altered by mating is found to be sex specific, this can be attributed to the distinct reproductive roles of the sexes. For instance, significant changes occurred by mating is clearly seen in females, such as increased food consumption, increased egg-laying and reduced receptivity to mating (Chapman et al. 1995; Liu and Kubli 2003; Rolff and Siva-Jothy 2002; Sgrò et al. 1998). Mating influences increased food intake in female Drosophila melanogaster (Carvalho et al. 2006) and alters their dietary preferences (Ribeiro and Dickson, 2010; Vargas et al. 2010). This is because copulation, ejaculation and oogenesis stimulates their desire for nutrients. Whereas in males it has been found that they primarily work for sperm replenishment and seminal fluid storage. At the same time in some insects, it induces their efforts in nuptial gifts (Sirot et al. 2009). Multiple studies have reported that many insect species show sex specific feeding preferences. For example, in Madagascar Hissing Cockroach, Gromphadorhina portentosa Schaum, female shows strong preference for food rich in amino acids, in contrast males tend to select carbohydrate rich food (Carrel and Tanner 2002). In Spodoptera litura (Fabricius) both males and females adjust their food selection on the basis of macronutrients present in food (Lee 2010). This study was conducted to investigate mating induced dietary shift in adult P. dissecta to regulate their nutrient intake according to sex and mating associated energy expenditure.
Diversity in dietary preferences can be clearly found in ladybird beetles because of their wide prey range, as most of them are predaceous in nature (Dixon and Dixon 2000; Omkar and Pervez 2004; Pervez and Omkar 2003; Hodek et al. 2012; Omkar and Pervez 2016). Food relationships of Coccinellidae have always been actively studied, largely because of their economic value as biocontrol agent (Hodek 1996). Like many predators, when beetles have a choice between two or more prey types, they will often show a preference for one of them. Their prey suitability and preference are subjected to a number of factors, such as host plant constituents (Fouad 2021; Pervez and Chandra 2018; Guroo et al. 2017), plant architecture (Yu et al. 2019; Clark and Messina 1998), prey stage (Mishra et al. 2012), prey size, feeding experience (Zarghami et al. 2014), prey mobility and prey species (Provost et al. 2006; Yasuda and Ishikawa 1999). While multiple factors influence prey preferences in ladybirds, not much work has been done on the role of energy expenditure in determining prey choice. Depletion and reduction in an animal’s energy deposits represents an indicator of physiological stress, which may impose food selection pressure in organisms. We thus decided to assess the effect of energy expenditure on food choice of adult ladybirds, P. dissecta. Beetles spend time performing a variety of physical activities, like walking (in terms of searching for prey or escaping from predator), mating and reproduction that, depending on their duration and intensity require energy expenditure. It has been observed that under field conditions, ladybird beetles are exposed to predators, heterospecific and conspecific competitors leading to disruptions in feeding and in mating. In this study, energy expenditure was induced by subjecting adult of P. dissecta to different matings.
In this study, we examined whether the energy expenditure during mating is important for food choice in both sexes because mating induces significant behavioural and physiological changes in both sexes. To examine this, we used adult P. dissecta as an experimental model due to their wide prey range, high reproductive output, and abundance in local agricultural fields (Omkar et al. 2005) and distinct sexual dimorphism which makes it a suitable model to study mating and reproduction (Omkar and Pervez 2000).