Abstract
Simple SummaryThe brown marmorated stink bug is native to Asia and has invaded parts of Europe and North America where it causes considerable damage to a wide range of vegetable, fruit, and nut crops. Pistachios have become an important nut crop in California, and as this invasive stink bug moved into California, farmers needed to know about the potential damage from brown marmorated stink bugs. Here, we assessed pistachio yield loss and nut damage over a two-year period. The invasive stink bug was also compared with the native green stink bug and a native leaffooted bug. We found that brown marmorated stink bug adults cause more epicarp lesions (external damage) when recorded at harvest time than the native species; however, they did not cause more kernel necrosis (internal damage) than the two native species tested, which is a more relevant damage criterion for commercial production. We conclude that the brown marmorated stink bug could cause similar damage as the native species but note that the invasive stink bug’s numbers in California are still low and future damage levels will be dependent on this pest’s population density.California currently produces about a quarter of the world’s pistachios. Pistachio nuts are susceptible to feeding by stink bugs and leaffooted bugs; therefore, the invasive presence of the highly polyphagous brown marmorated stink bug, Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), is a concern to California pistachio growers. We aimed to assess the potential of H. halys to cause yield loss and nut damage to pistachios, which had not yet been assessed in the field. Over two years, terminal branch ends with pistachio clusters were enclosed in organdy cages from spring to fall and exposed to either H. halys, the native stink bug Chinavia hilaris Say (Hemiptera: Pentatomidae), or leaffooted bug Leptoglossus zonatus (Dallas) (Hemiptera: Coreidae), for 4–7-day feeding periods at different times of the season. We found that H. halys adults cause more epicarp lesions (external damage) when recorded at harvest time than the native species. They did not, however, cause more kernel necrosis (internal damage) than the two native species tested, which is a more relevant damage criterion for commercial production. There were no differences among insect species for any other recorded damage criteria. We conclude that H. halys could cause similar damage as the native species but note that H. halys population densities in California are still low and future damage levels will be dependent on this pest’s population density.
Highlights
Pistachios (Pistacia vera L.) have over 264,000 bearing acres (106,837 ha) in California, which produce about a quarter of the world’s pistachios [1]
The interaction between insect species and pistachio phenology was significant (GLMM, df = 9, 13627, χ2 = 39.06, p < 0.001): Leptoglossus zonatus produced more epicarp lesions during ‘midseason’ than the other two species, but the trend of decreasing epicarp lesions with the progressing season was similar for all insect species (Figure 2a)
When H. halys nymphs were included in the analysis (LM, df = 3, 48, F = 392.96, p < 0.001), they had significantly shorter rostra than C. hilaris (Tukey multiple comparisons, t = 11.015, p < 0.001). This first field study of H. halys in pistachios shows this invasive pest can cause damage to pistachio nuts throughout the season, resulting in epicarp lesions and kernel necrosis. This is consistent with the type and extent of damage caused by native stink bugs and leaffooted bugs [4], and confirms the formation of kernel necrosis from H. halys feeding, which was previously shown in a laboratory study [22]
Summary
Pistachios (Pistacia vera L.) have over 264,000 bearing acres (106,837 ha) in California, which produce about a quarter of the world’s pistachios [1]. The most important insect pest in Californian pistachio orchards is the navel orangeworm Amyelois transitella (Walker) (Lepidoptera: Pyralidae) [3], but there is a complex of heteropteran pests including Miridae and Rhopalidae (often referred to as ‘small bugs’), as well as Pentatomidae (stink bugs) and Coreidae (leaffooted bugs), that can be grouped together as ‘large bugs’, which can cause significant yield reductions especially in organic production [4,5]. The type and severity of pistachio damage from heteropteran feeding depend largely on the insect size and thereby the length of its mouthparts, and the physiological maturation of the fruit [4,14]. Common large bug pests in Californian pistachio production include the stink bugs Thyanta pallidovirens (Stål), Chlorochroa sayi Stål, and C. uhleri (Stål), as well as Chinavia hilaris (Say) (formerly Acrosternum hilare)
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