Data were summarized separately for each of the two years. For each year, a Chi square goodness of fit test was used to examine whether or not there were equal levels of a damage type among three treatment categories within a variety. If there was a significant difference in damage among the three treatments in a variety, then Fisher’s Exact tests were used to compare each pair of treatments. Tests were considered significant at the p < 0.05 level. This study examined the impact from feeding by two Leptoglossus species, L. clypealis and L. zonatus, on developing almonds in four varieties during the growing season. Almonds of each variety were caged with equal numbers of adults of each species to determine the potential impact. Early in the growing season, leaf footed bugs fed by puncturing their stylets into the developing almond accessing the jelly-like immature kernel. In both years, almond drop in the controls was low,blueberry pot size while almond drop in cages with Leptoglossus adults was twice as high. The first month of the study in April had higher levels of almond drop than in the later weeks of the study in May. The time in April corresponded to weeks when the almond shell could be punctured mechanically and indicated that the developing almonds were more vulnerable than in May, when the shell had hardened.
Overall, almond drop during the season was lower from L. clypealis than from L. zonatus. This may be due to the smaller size of L. clypealis compared to L. zonatus adults. Monterey had higher levels of almond drop from L. zonatus in both years than the other three varieties. Feeding by leaffooted bugs also caused significant damage to almonds in the form of nut strikes, kernel necrosis and shriveled kernels. The final damage observed at almond harvest was higher overall from feeding associated with L. zonatus than L. clypealis. Other studies have found significant crop damage from the presence of Leptoglossus clypealis and Leptoglossus zonatus. For example, feeding by L. zonatus in physic nut increased fruit abortion. A study of L. clypealis on pistachio found that when one adult L. clypealis fed for 48 h, the number of fruits dropped was higher on average than in controls. L. zonatus feeding in citrus resulted in spots on the outer citrus rind and feeding on satsuma mandarin by 1–3 adults for 14 days resulted in 37.5–100 percent of premature fruit abortion. Studies such as these demonstrate the need for controls, to determine the natural level of fruit abscission, and which damage symptoms can be attributed to insect feeding.Developing almonds may be more susceptible than mature almonds to feeding damage from Hemiptera, as has been observed in pistachios. In the present study, the almond shell could be punctured by an insect pin until the end of April but by May, the external almond shell became too firm to puncture and almonds were presumed no longer susceptible to bug feeding. The majority of almond drop in the four varieties occurred in the first few weeks of observations.
After the fifth observation week of caging Leptoglossus on branches, the percent almond drop decreased relative to the early weeks of observations and remained minimal. This agrees with an early study by Haviland, where almonds were artificially damaged by puncturing, and more almond drop occurred in April than in May. Our study was a no-choice test, where bugs were caged with only one almond variety; when offered one variety and no choice, the levels of almond drop were similar among the four varieties. However, in a natural field-study where almond drop was assessed after a Leptoglossus infestation, higher levels of almond drop were observed in Fritz . When provided with a choice of varieties, L. clypealis appeared to prefer to feed on Fritz. Almonds on the trees that were fed on by bugs later in their development may not drop but can suffer downgrades or rejects at harvest as observed for other crops. In pistachios, Leptoglossus sp. was capable of causing feeding damage to the pistachio kernel even after the hardening of the shell. Michalides et al. found that the large bugs including Leptoglossus clypealis were able to cause pistachio kernel damage until late June, when nut development was at the final stage. A late season feeding study of large bugs in pistachios found that kernel necrosis could range up to 20%. The vulnerability of almonds later in the growing season has not been fully investigated. Leptoglossus may cause feeding injury to almonds which are well developed, and thus might be monitored and controlled throughout the growing season. In other systems, fruit size and shell hardness has been found to influence the level of insect feeding damage.
Feeding on physic nut by Leptoglossus zonatus resulted in larger fruits having more seed abortion and feeding resulted in more shriveled or damaged nuts; similarly, some varieties of olives with larger fruits had a higher infestation rate by the olive fruit fly, Bactrocera oleae. In hazelnut, shell thickness was not correlated with damage by brown marmorated stink bugs, Halyomorpha halys, and the authors suggested that shell thickness should not be a criterion to select cultivars resistant to H. halys. Follett et al. reported that husk and shell thickness in macadamia nut do not primarily determine susceptibility of fruits to Nezara viridula. Hull width could relate to the susceptibility of the almond to feeding damage by the two leaf footed bug species. Although there was a significant difference in hull widths between Nonpareil and Fritz, there was no relationship between hull width and almond drop. In addition, the hull width of Nonpareil was significantly thicker than Fritz, but hull strikes on Nonpareil and Fritz from L. clypealis and L. zonatus did not vary significantly, and nut strikes were also not higher on Fritz. This suggests that damage from Leptoglossus feeding on these two varieties was not influenced by hull width . In 2015, higher levels of damage were observed in all four varieties compared to 2014, but again did not relate to the hull width differences . The final assessment of damage from L. zonatus and L. clypealis included hull strikes, nut strikes, kernel necrosis and shriveled kernels. Insects probing the hull results in hull strikes and suggest that the internal almond kernel may be damaged. Nut strikes, almond kernel necrosis and shriveled kernels can lead to downgrades or unsellable product. In both years of this study, the cages with both Leptoglossus species typically had higher levels of hull strikes and nut strikes than in the control cages. In 2014, L. clypealis feeding did not result in significant kernel necrosis compared to controls in any variety,plant raspberry in container but L. zonatus had higher levels of kernel necrosis than controls in Monterey and Carmel; in 2015, kernel necrosis was consistently higher in L. zonatus cages than in controls. In 2014, the percent of shriveled kernels at harvest did not vary between the controls and the L. clypealis cages in any variety. However, the percent of shriveled kernels was higher in L. zonatus cages than controls in two varieties, Monterey and Carmel, while in 2015, the cages with L. zonatus resulted in higher levels of shriveled kernels in Nonpareil and Monterey. Research has similarly found that insect feeding damage varies among almond varieties as well as in varieties of other crops such as in apple, blueberry and olives. Hull strikes that are characterized by a spot on the external portion of the almond could correspond directly to internal damage such as nut strikes or almond damage. The number of external hull strikes was similar to the number of internal nut strikes and damaged nuts for L clypealis. However, for L. zonatus in both years, the number of hull strikes recorded was often lower than the number of nut strikes or damaged nuts. Hull strikes could be used as a proxy to estimate the number of almonds with internal damage such as nut strikes or kernel necrosis which might later be unsellable . Evidence of hemipteran probing and feeding has been used as a proxy for feeding damage in other systems. Nut strikes are expected to occur due to feeding injury from sucking insects where insects probe their mouth parts into fruits during feeding.
In 2014, nut strikes on the four varieties due to L. clypealis was an average of 15%, while nut strikes from L. zonatus averaged 24.75%; in 2015, L. zonatus similarly had higher numbers of nut strikes than in controls. In contrast to the relationship found between hull strikes and other kernel damage from Leptoglossus feeding, in other crops, the presence of holes, spots, or mouth part stylet sheaths on a fruit has not always been found to translate directly into fruit damage. For example, Wiman et al. reported that in blueberry, external fruit probing by Halyomorpha halys indicated by a high numbers of stylet sheaths had very little internal damage as measured necrosis and discoloration. However, in apples, the punctures by the mullein bug were related to internal damage, which is more similar to what was observed in this study. Interestingly, some kernel necrosis was observed in control cages of all the varieties in both years. In 2014, the controls in each variety had few or no almonds with hull strikes yet had some level of kernel necrosis. A similar pattern was observed in 2015 as well. In cages with feeding by Leptoglossus there was a higher level of kernel necrosis than in controls. It should be noted that Leptoglossus feeding does not account for the kernel necrosis observed in the controls, but perhaps another agent such as a pathogen could be responsible. Studies such as the one herein with caged insects help to determine the damage symptoms which can be attributed to insect feeding. Similarly, a study of pistachios used caged bugs to determine which damage symptoms could be attributed to feeding. Pathogens may be responsible for a percentage of kernel necrosis observed in controls in this study, but this would need to be investigated. The final damage parameter, shriveled kernels, was also observed in all the controls, similar to the pattern observed for kernel necrosis. It should again be noted that this is a natural type of damage which occurs in the crop, and it is not only induced by feeding of L. clypealis and L. zonatus. However, in L. zonatus cages, two varieties had levels of shriveled kernels which exceeded the controls. Drosophila suzukii, also known as the spotted wing drosophila , is a vinegar fly originating from Southeast Asia. SWD was first detected in North America in August 2008 in Santa Cruz County, California, where it was observed infesting strawberries and caneberries.1,2 In 2009, SWD was detected in Washington, Oregon, and Florida. By 2010, SWD was detected in Utah, Mississippi, North Carolina, South Carolina, Wisconsin, and Michigan in the United States, and Alberta, Manitoba, Ontario, and Quebec in Canada.Recent trapping indicates that SWD can be found in virtually any region of North America where host fruit are available. A coincidental invasion of SWD with a genetically distinct population has also been observed in Europe, with initial detections in both Spain and Italy in 2008, followed by its spread throughout the continent.In North America, SWD is primarily a pest of berries and cherries. In Europe, it is reported to also damage a number of stone fruits and grapes. Unlike native vinegar flies in North America and Europe, female SWD possess a serrated ovipositor that can pierce the skin of healthy, soft-skinned fruits to lay eggs. These eggs quickly develop into larvae, which consume the fruit and render it unmarketable. The only other Drosophila species known to oviposit in sound, marketable fruit is Drosophila pulchrella Tan. This species is native to Japan.1 Growers have attempted to mitigate crop damage risk by applying additional insecticide, harvesting more frequently, performing field sanitation, and implementing trapping programs to detect SWD populations. These management practices are costly and many growers still face significant yield losses from SWD infestations.Raspberry producers are perhaps the most affected by SWD’s invasion among California commodities, although producers of blueberries and cherries have experienced substantial losses too. Strawberry producers have experienced lower damage rates and primarily on the lower-value fruit produced for processing.