Importance of wildflowers in Orius insidiosus (Heteroptera: Anthocoridae) diet

1 Introduction

Non-crop floral resources are used to increase abundance and fitness of natural enemies by providing hosts for parasitoids, prey for predators, and additional food resources such as pollen or nectar (Symondson et al. 2002; Wong and Frank 2013). This is particularly critical for omnivorous predators that often benefit from a diet of both prey and plant material (Coll and Guershon 2002; Leon-Beck and Coll 2007; Wong and Frank 2013). Flowering plants can therefore be considered in conservation biological control strategies in the form of banker plants, flower strips or hedgerow plantings to increase recruitment and survival of predators, particularly in monoculture systems with or without a time-limited resource of suitable pollen (Coll and Guershon 2002; Lundgren et al. 2009; Wong and Frank 2013; Waite et al. 2014).

Orius species (Hemiptera: Anthocoridae), also called minute pirate bugs, are generalist predators that feed primarily on thrips but also are known to feed and successfully reproduce on other pests affecting vegetable crops such as whiteflies, aphids, and mites (Lundgren et al. 2009; Wong and Frank 2013; Bernardo et al. 2017). Several species are known to feed on pollen at the nymphal and adult stage in addition to prey, which is proposed to affect survival and development time as well as reduce cannibalism (Kiman and Yeargan 1985; Coll and Guershon 2002; Leon-Beck and Coll 2007; Calixto et al. 2013; Wong and Frank 2013; Bueno et al. 2014). In a previous study, a diet of pollen from pepper Capsicum annuum L. cv ‘Black pearl’ (Solanaceae) combined with thrips increased Orius insidiosus (Say) longevity and size and decreased nymphal development time (Wong and Frank 2013). There is also evidence that the addition of pollen may reduce cannibalism, which has been described as a potential limiting factor in mass rearing of O. insidiosus for commercial use (Leon-Beck and Coll 2007; Calixto et al. 2013; Bueno et al. 2014).

Bidens alba L. and Coreopsis leavenworthii Torrey & Gray are two Asteraceae host plants of Orius spp. native to Florida that have been shown to increase natural enemy and pollinator services (Funderburk 2009; Tyler-Julian et al. 2018; Abdelmaksoud et al. 2020). In addition, these plant species serve as hosts for less damaging native thrips species (Thysanoptera: Thripidae) including Frankliniella bispinosa Morgan and Frankliniella tritici (Fitch), which have been shown to outcompete the worldwide pest F. occidentalis (Pergande) (Baez et al. 2004; Reitz et al. 2006; Paini et al. 2008; Northfield et al. 2011). For this reason, B. alba and C. leavenworthii are potential candidates to be used as companion plants to enhance O. insidiosus fitness (Norcini et al. 2009; Tyler-Julian et al. 2018). Nevertheless, there is limited research documenting the direct effects of B. alba and C. leavenworthii on the overall fitness of Orius spp., perhaps due to their perceived status as weeds. There remains a need to investigate their potential to improve O. insidiosus fitness and abundance, and to provide justification for their use in improving conservation biological control of thrips and other pest species.

2 Materials and methods

3 Results

3.1 Female survival

There was a significant effect of adding C. leavenworthii and B. alba in a diet for adult female O. insidiosus survivorship (LR = 21, d.f. = 4, P < 0.001) (Figure 1). Adults given diets containing C. leavenworthii flowers + F. tritici, B. alba + F. tritici, and C. leavenworthii flowers alone survived significantly longer (11.56 ± 12.9, 14.89 ± 0.96, and 12.89 ± 1.06 days, respectively) than those with a diet of B. alba flowers only or F. tritici thrips only (7.44 ± 1.32, 8.00 ± 0.95 days, respectively). A diet of B. alba flowers only did not differ from a diet of thrips alone.

Figure 1:

Survival distribution of adult female Orius insidiosus when fed a diet of thrips F rankliniella  tritici, flowers of Bidens alba only, flowers of B. alba + F. tritici, flowers of Coreoposis leavenworthii only, or flowers of C. leavenworthii + F. tritici as a function of hours until event up to 480 h (20 days).

3.2 Nymphal development

All 100 nymphs survived to adulthood. There was a significant difference among treatments for the nymphal development time (F _4,95 = 3.62; P = 0.0086). O. insidiosus fed with a diet of B. alba and F. tritici had a reduced development time as compared to O. insidiosus nymphs provided with a diet of F. tritici alone (P < 0.05). O. insidiosus fed on diets with C. leavenworthii, C. leavenworthii + F. tritici, or B. alba alone did not differ in development time as compared to the O. insidiosus fed on thrips only (P > 0.05) (Figure 2).

Figure 2:

Adult emergence time (mean ± SEM days) for Orius insidiosus nymphs when fed a diet of thrips F rankliniella  tritici, Bidens alba only, B. alba + F. tritici, Coreopsis leavenworthii only, or C. leavenworthii + F. tritici. Different lowercase letters indicate a significant difference among treatments (P < 0.05).

3.3 Cannibalism

Cannibalism events were quite rare throughout all the experiment, with only 10 % for the O. insidiosus females provided with O. insidiosus nymphs only. After 48 h, there were no significant differences in instances of cannibalism of O. insidiosus nymphs or adults for any of the diet treatments (chi-square = 6.6554; d.f. = 5; P = 0.2476) (Figure 3).

Figure 3:

Proportion of Orius insidisous cannibalism after 48 h when fed a diet of thrips F rankliniella  tritici, Bidens alba only, B. alba + F. tritici, Coreopsis leavenworthii only, C. leavenworthii + F. tritici, or a control with no food. The proportion was determined by the number of nymphs cannibalized divided by the total number of nymphs in each treatment (5). There was no significant differences among treatments (P > 0.05).

4 Discussion

The current study suggests that adding flowers from B. alba and C. leavenworthii has a positive impact on O. insidiosus fitness. However, the effects varied by treatment: while B. alba reduced nymphal development time and increased survival when combined with thrips prey, C. leavenworthii increased O. insidiosus female survival by itself as compared to a diet with thrips only. However, no effect on development time was found for C. leavenworthi. Survival of O. insidiosus females fed with thrips and flowers (15 days for B. alba and thrips and 12 days for C. leavenworthi and thrips) was slightly higher than from other studies (14 days on average in Calixto et al. (2013) with a commercial mix of pollen from various flowers, 8 days in Wong and Frank (2013) with pepper flowers). Similarly, development times of O. insidiosus nymphs in this study (from 9.5 days for B. alba + thrips to 12 for thrips only) were longer than in Wong and Frank (2013) (7–8 days) but on a similar range compared with other studies (10–13 days in Mendes et al. (2002), 11–15 days in Bernardo et al. (2017)).

Previous studies have demonstrated the benefits of adding pollen to the diet of Orius spp. Wong and Frank (2013) and Waite et al. (2014) found that the addition of pollen from ornamental pepper cultivars (cv. ‘Black Pearl’ and ‘Purple Flash’) increased O. insidiosus survival and decreased nymphal development time, and a pollen blend of several plants including Eucalyptus sp. (Myrtaceae), Bidens pilosa L. (Asteraceae), and Citrus sp. (Rutaceae) shortened nymphal development compared to a diet of prey only (Bernardo et al. 2017). In this study, because both plants were Asteraceae, we did not separate the pollen that are intricated within the tiny disc flowers. Therefore, we cannot rule out that Orius may also have fed on other parts of the flower in addition to the pollen. The results from this study regarding O. insidiosus female survival differ from that of previous studies where survival was not affected by the addition of pollen to a diet when compared to a diet of thrips prey or pollen only (Wong and Frank 2013). However, in all cases, including in the current study, Orius spp. fed a diet containing pollen have similar or increased longevity. The extent to which these effects occur may be dependent on the nutritional value of pollen, which stresses the importance of choosing appropriate pollen sources (Waite et al. 2014; Bernardo et al. 2017).

O. insidiosus is a common and popular commercial biological control agent used against F. occidentalis and other pests. As an omnivorous predator, they are known to utilize plant materials in addition to prey. When prey availability is low, however, many predators exhibit cannibalistic behaviors, including O. insidiosus (Leon-Beck and Coll 2007; Bueno et al. 2014). This study hypothesized that cannibalism would be reduced with the addition of B. alba and C. leavenworthii flowers than on prey alone as supplementing with plant material is expected to benefit nutrition (Leon-Beck and Coll 2007). Results, however, showed no difference in cannibalism amongst O. insidiosus because of diet and are supported by a previous study by Leon-Beck and Coll (2007) who found no differences in cannibalism occurrence in another Orius species, Orius laevigatus (Fieber), when provided with prey, pollen, or both. Interestingly, there was very low cannibalism (≤10 %) in all treatments, including no prey or pollen, which suggests cannibalism among O. insidiosus may be minimal except in cases of extreme stress that may occur in industrial rearing (i.e., low food availability combined with lack of shelter or hiding spots (Bueno et al. 2014)).

The use of B. alba and C. leavenworthii flowers to supplement a prey diet can increase O. insidiosus survival and decrease nymphal development time, with some variations, depending on the pollen source. A shorter development time is considered a desirable life history trait for a biological control agent as it reduces the non-reproductive period and the stage where the individual is the most susceptible to intra-guild predation or cannibalism, it also allows for the rapid deployment of the agent to control the pest population (Facon 2011; Wong and Frank 2013; Sentis et al. 2022). In addition, shorter development time and higher adult survivorship is usually corelated to higher fecundity in Orius sp. (Tommasini et al. 2004: Calixto et al. 2013). The results from this study suggest that these two plants may be valuable assets for increasing and sustaining O. insidiosus populations through conservation biological control and augmentative biological control in the case of mass rearing.