Boron compounds are effective on Sitophilus granarius (Coleoptera: Curculionidae) and Rhyzopertha dominica (Coleoptera: Bostrichidae)

The granary weevil, Sitophilus granarius (Linnaeus, 1875) (Coleoptera: Curculionidae), and the lesser grain borer, Rhyzopertha dominica (Fabricius, 1792) (Coleoptera: Bostrichidae) are two of the most damaging stored grain pest species worldwide. The damage caused by these insects is significant in terms of loss of both quality and quantity of the product (Ertürk, 2021). Both species might be also present in the post-harvest distribution channels, are widely known to be cosmopolitan, and product loss due to these pests might reach as high as 10–40% in places where modern storage techniques are unavailable (Ahmad et al., 2022). In heavy infestations, remnants of the insect integument and feces undergo physical and chemical degradation, leading to the formation of dirt and mold in the products. Consumption of such products might also lead to allergic reactions, anorexia, and various infections (Gorham, 1991; Athanassiou et al., 2011). As a result, developing control measures against these pests is critical for the protection of stored products. The primary control method for these insects is the repeated application of synthetic insecticides (Lampiri et al., 2023). However, the use of such insecticides has several drawbacks, such as being toxic to mammals, residual issues, and the development of resistance over time (Arthur, 1996; Mortazavi et al., 2020). Thus, research efforts have concentrated on the development of alternative control methods and natural products (Arthur, 1996; Habes et al., 2006; Toprak et al., 2006, 2013; Rani, 2012; Alkan, 2020; Ertürk et al., 2020; Dissanayaka et al., 2020; Uçar et al., 2020; Doğan et al., 2021; Güney et al., 2021a, 2021b; Alkan et al., 2023; Atay et al., 2023).

One alternative in pest control is boron-containing compounds. Such compounds are effective in killing a wide range of pests including insects, mites, algae, fungi, and higher plants. They have been used to kill ants, fleas, termites, cockroaches, wood-boring insects, and fungi that cause wood decay (Myles, 1994; Zurek et al., 2002; Cox, 2004; Habes et al., 2006; Sarwar, 2016). In particular, studies have shown that boron applications are effective in protecting wood from termites (Grace 1990, 1991; Myles, 1994; Su et al., 1994; Ahmed et al., 2004; Kartal et al., 2004). Boron-based ant bait products are also commercially available for controlling a wide range of ant species, mainly indoor pest ants (Sarwar, 2016; Chen and Oi, 2020). Additionally, boron compounds, when used correctly, have a promising potential with low toxicity to vertebrates and the environment (Gentz and Grace, 2006) and a lack of insect resistance compared to organic insecticides (Gore and Schal, 2004). Despite this potential, there have been only a few studies on the effect of boron-containing compounds on stored product pests. Korunić et al. (2017) found that disodium octaborate tetrahydrate is effective on Sitophilus oryzae (Linnaeus, 1763) (Coleoptera: Curculionidae) and does not reduce the bulk density of the treated grains. Korunić and Fields (2020) reported that dust or wettable powder formulations of disodium octaborate tetrahydrate (F3DOTZ) were highly effective on S. oryzae and R. dominica. In another study, a mixture of boric acid with silica led to complete mortality for all life stages of the khapra beetle Trogoderma granarium Everts, 1899 (Coleoptera: Dermestidae) when added as 40 g per 1 kg wheat (Falah and Azher, 2020). It is necessary to conduct more studies with different boron compounds, in particular against stored product pests to fully understand the potential of boron in stored product pest control.

Another research gap on the insecticidal potential of boron is the uncertainty regarding the mode of action of boron in insects as the data are very limited. For example, boric acid acts as a midgut poison as well as an abrasive on the insects’ cuticle by absorbing waxes from the insects’ outer surfaces, which leads to desiccation and eventually death (Ware, 2000; Sarwar, 2016). On the other hand, boron has been shown to inhibit lipogenesis which leads to weight loss in mammalians (Hasbahceci et al., 2013; Doğan et al., 2017; Abdik et al., 2019; Białek et al., 2019; Kuru et al., 2019). However, this has not been addressed yet in insects. Therefore, it is necessary to investigate the exact mode of action of boron compounds for their widespread use in pest control.

In the current study, we aimed to investigate the insecticidal potential of four boron compounds synthesized from Turkish ore beds, disodium octaborate tetrahydrate (Etidot-67), calcium metaborate (CMB), ammonium tetrafluoroborate (ATFB), and sodium metaborate tetrahydrate (SMT) as traditional chemical insecticide alternatives, on S. granarius and R. dominica. The progeny productions (F1) were also assessed following a 45-day exposure period. As boron interferes with lipid metabolism and induces weight loss in mammalian models, we also examined whether the two most effective compounds, CMB and Etidot-67 have an impact on insect lipid metabolism, by quantifying the insect triglyceride (TG) levels upon treatment. The effect of boron compounds was also investigated in terms of body weight. Finally, scanning electron microscopy (SEM) analyses were conducted to understand the structure of the corresponding boron compounds.