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Honeydew, a sugary excretion produced by sap‐feeding insects, plays a pivotal role in shaping intricate interactions between insects and plants. This review explains the multifaceted aspects of honeydew, beginning with an overview of its production mechanisms and factors influencing its variability across insect species and plant hosts. Exploring its composition, we examine the chemical components and nutritional aspects, highlighting variations based on insect species and plant sources. The impact of honeydew on microbial communities is explored, shedding light on its role in influencing the diversity and abundance of microorganisms. Furthermore, the review investigates how honeydew affects pest behaviour and population dynamics, elucidating plant responses to honeydew deposition. In the realm of biocontrol, we examine the intricate relationships between honeydew and natural enemies, considering potential implications for integrated pest management. Beyond these individual components, the paper discusses the broader ecological consequences of honeydew in ecosystems, emphasizing the interconnected relationships between insects, plants and microorganisms. The review concludes by identifying research gaps and suggesting future directions, recognizing the need for further investigation into areas with potential applications for agriculture and ecology. This review provides a comprehensive synthesis of the current understanding of honeydew's significance in insect–plant interactions, offering insights for both researchers and practitioners in the field. [ABSTRACT FROM AUTHOR]

Herbivore feeding often increases secondary metabolite production in plants. These herbivore‐induced plant proteins might end up in honeydew excreted by phloem‐feeding insects. This is important because honeydew is one of the most abundant and accessible carbohydrate sources for natural enemies in many agroecosystems and these proteins can thus mediate many tri‐trophic interactions. Here, we hypothesized that defensive metabolites induced in the phloem by herbivory accumulate in the honeydew excreted by phloem‐feeding insects and, consequently, affect the fitness of the herbivores' natural enemies that feed on it. We used a tri‐trophic system consisting of citrus plants, the mealybug Planococcus citri and its primary parasitoid Anagyrus vladimiri. First, we assessed A. vladimiri fitness when fed on P. citri honeydew. We then collected honeydew of seven phloem‐feeding insects, including P. citri, and analysed their protein content. Finally, we analysed the effect of superoxide dismutase (SOD), an antioxidant enzyme associated with plant defences that was commonly found in the analysed honeydews, on A. vladimiri fitness. The fitness of A. vladimiri increased when fed on honeydew compared to a sucrose‐based diet, demonstrating that honeydew can contain compounds that benefit natural enemies. Proteomic analyses showed that defence‐related plant proteins were present in honeydew of seven phloem‐feeding insects analysed. Among these, the enzyme SOD was present in honeydew of all of them. Moreover, the levels of SOD were 10‐fold higher in the phloem of plants infested by P. citri than in that of uninfested plants. SOD was also actively excreted in P. citri honeydew, and we proved that it increases the fecundity of the parasitoid A. vladimiri. We conclude that enzymatic proteins induced by herbivory in the phloem and involved in plant defence, accumulate in the honeydew excreted by phloem‐feeding insects and, contrary to the current paradigm, at least some of these can have positive effects on the third trophic level. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Simple Summary: The spotted lanternfly (SLF) is an invasive generalist that is spreading throughout the eastern United States. They feed in large aggregations, but the mechanisms they use to form these aggregations and find each other for mating are poorly understood. Laboratory evidence that they use pheromones is based on volatiles from their bodies and from honeydew excretions, but, due to their broad sensory capabilities, the pheromone components have been difficult to isolate and identify. This is the first evidence gathered in a field study that demonstrates, using naturally collected SLF odors as lures, that volatiles from SLF bodies and honeydew are both required to attract males at mating time and females during oviposition time. Using semiochemicals collected from spotted lanternflies Lycorma delicatula (Hemiptera: Fulgoridae) (SLF) and deployed in the field with circle traps, we demonstrated that SLF responded to SLF pheromones: in particular, this was the case for males while seeking mates and for females while ovipositing. The attractants consisted of SLF body extract emitted from diffuser lures and SLF honeydew on burlap ribbons, collected from heavily infested locations. Traps with attractants were deployed in field sites with very light SLF infestations to avoid competing signals of pre-existing aggregations. The number of SLF equivalents emitted by each diffuser per trapping period was used in a dose–response analysis. Three trees per block received either (1) a control hexane lure and a clean ribbon, (2) a lure containing SLF extract and a clean ribbon, or (3) a lure containing SLF extract and a honeydew-laden ribbon. Ten blocks were sampled three times per week for twelve weeks. We found a significant positive dose–response by males to SLF body extract only in the presence of SLF honeydew, indicating a synergistic effect between honeydew volatiles and body volatiles. This dose–response occurred for five weeks after mating started, after which males no longer responded. Subsequently, females had a significant positive dose–response to SLF extract only in the presence of honeydew when oviposition was their primary activity, continuing for two weeks, suggesting that females may use pheromones to aggregate for oviposition. The extract in the absence of honeydew did not result in a positive dose–response, nor did the hexane control. These findings suggest that SLF respond synergistically to the combination of pheromones present in both SLF honeydew and SLF bodies. Thus, combining key components from both sources may aid the development of semiochemical lures for SLF. [ABSTRACT FROM AUTHOR]

Although blossom and honeydew honeys are produced from different nectar sources, it is very difficult to distinguish them. In this study, physicochemical and biochemical properties were compared to distinguish honeydew and blossom honeys obtained from different botanical sources. The honeys of pine (Pinus spp.) and oak (Quercus, spp.) were used as honeydew honey, and chestnut (Castania sativa L.) and highland honey were used as blossom honey. Turbidity, specific optical rotation (SOR) [α]20, electrical conductivity (EC), CIEL* a*b color parameters, and moisture and pH were assessed as physical parameters. Proline, invertase activity, sugar composition, total phenolic and flavonoid contents, and antioxidant capacity were used as biochemical properties. It was determined that SOR values were the most important parameters in distinguishing honeydew and blossom honeys. Turbidity stands out as a crucial factor in differentiating between pine and oak honeys. Except for chestnut honey, electrical conductivity, CIE color Lab values, and sugar profiles were identified as additional distinguishing factors among the tested honeys. [ABSTRACT FROM AUTHOR]

Honeydew from Hemipteran insects serves as carbohydrate source to beneficial insects but also to various microorganisms. Microbial volatile organic compounds (mVOCs) may play diverse roles in herbivore–microbe–natural enemy interactions. However, the functional significance of mVOCs from aphid honeydew remains largely unclear. In this study, a total of seven cultivable bacteria from Sitobion miscanthi honeydew have been isolated and identified based on 16S rRNA technique, which included Lysinibacillus fusiformis, Erwinia aphidicola, E. tasmaniensis, Acinetobacter bereziniae, Klebsiella quasipneumoniae subsp. Similipneumoniae, Staphylococcus capitis and Bacillus safensis subsp. safensis. One bacterial strain, L. fusiformis MH1, was found to be most attractive to Aphidius gifuensis parasitic wasp in Y-tube olfactometer. Two compounds, namely 1-ethyl-2-methylbenzene and 2-butyl-1-octanol, were emitted from L. fusiformis MH1 and were attractive to A. gifuensis and identified by using coupled gas chromatography–electroantennography and coupled gas chromatography with mass spectrometry. Application of bacterial and mVOCs formulations in crop field resulted in significant aphid abundance decrease associated with higher parasitism rates compared with control. Our results indicated that some microbes in aphid honeydew could manipulate the herbivore–natural enemy interactions and could be developed as a novel alternative for environmentally friendly biological control of aphids. [ABSTRACT FROM AUTHOR]

The invasive mealybug Delottococcus aberiae De Lotto (Hemiptera: Pseudococcidae) has become a key pest in Mediterranean citrus. This mealybug species excretes honeydew that can be consumed by ants, which may give rise to mutualistic relationships and increase the invasibility of this exotic pest. Here, we studied the interaction between D. aberiae and ants in 16 citrus orchards located in the main citrus-growing area of Spain (Valencia) during two consecutive years. Four native ant species were observed feeding on D. aberiae honeydew, and Lasius grandis Forel (Hymenoptera: Formicidae) represented more than 95% of these ants. Lasius grandis was observed attending D. aberiae throughout the year and in all the orchard sites where the mealybug was present. Mealybug colony size had a positive effect on both relative and absolute ant-attendance by L. grandis, but these interactions varied across seasons. Moreover, we found a positive correlation between L. grandis activity and D. aberiae density in all citrus orchards. Our results suggest that the native ant L. grandis and the invasive pest D. aberiae have established a mutualistic association that promotes the establishment and accelerate the invasion of D. aberiae in Spanish citrus orchards. Further research with the aim of evaluating whether the management of this ant species can improve the control of D. aberiae in citrus would be recommended. [ABSTRACT FROM AUTHOR]