Association of Botryosphaeria Panicle and Shoot Blight of Pistachio with Injuries of Fruit Caused by Hemiptera Insects and Birds

Panicle and shoot blight of pistachio caused by species of Botryosphaeriaceae fungi remains one of the major diseases of pistachio in California, with the highest potential for crop destruction because buds and fruit clusters (panicles) are killed. Pistachio fruit can also be damaged by various insect pests. For instance, hemipteran insects are considered major pests of pistachio and can attack maturing fruit, causing necrotic areas on the fruit epicarp (epicarp lesion). Surveys in pistachio orchards showed a putative association of punctures of pistachio fruit with infection by Botryosphaeriaceae fungi, resulting in panicle and shoot blight. This study was undertaken to determine any association of Botryosphaeriaceae fungi with fruit bearing epicarp lesions and whether hemipteran insects can actively carry propagules of the pathogens to healthy fruit and cause disease. Three large insects of the order Hemiptera (Thyanta pallidovirens, Acrosternum hilare, and Leptoglossus clypealis) were used in pathogen-spread and infection experiments. The most frequently isolated species of the family Botryosphaeriaceae in pistachio, Neofusicoccum mediterraneum, was used in these transmission experiments. Significantly higher incidence of fruit infected by N. mediterraneum was recorded when pistachio clusters were sprayed with a spore suspension of N. mediterraneum and caged with the above insects than the level of infected fruit sprayed similarly with the pathogen but caged without any insects. Furthermore, increasing the number of insects caged with pistachio clusters resulted in an increase of insect feeding punctures and, subsequently, disease incidence. Similarly, increasing the number of wounds per fruit made with a needle, simulating injuries caused by the insect’s stylet, resulted in significantly higher incidence of infected fruit than for wounded fruit with fewer injured sites. In addition, bird-injured fruit were also associated with higher incidence of panicle blight than fruit not injured by birds, especially in orchards with high disease incidence. In laboratory experiments, wounding or applying fruit sap to nonwounded fruit resulted in significantly higher incidence of infected fruit than in nonwounded fruit without sap. In field experiments, wounding of fruit before or after inoculation with N. mediterraneum resulted in higher disease incidence than nonwounded and inoculated fruit. Additionally, fruit sap enhanced initial mycelial growth of N. mediterraneum. Protecting fruit clusters from injuries by hemipteran insects or birds using mesh cages significantly reduced the incidence of panicle and shoot blight. The association of wounding by hemipteran insects and birds with high incidence of infected pistachio fruit may explain partially the broad distribution of Botryosphaeria panicle and shoot blight among pistachio orchards of the central San Joaquin Valley, even in areas where inoculum sources are not nearby.

Using Microscopy to Assess Chorion Structural Integrity and Parasitoid Oviposition Sites on Stink Bug (Hemiptera: Pentatomidae) Eggs

Previous efficacy studies found that many insecticides used by growers could be having an adverse effect on egg parasitoids (Telenomus podisi) developing in the eggs of the brown stink bug (Euschistus servus), while unhatched stink bugs experienced lower levels of mortality. One plausible explanation for this was that insecticides might enter parasitized eggs more readily via oviposition wounds. Parasitized E. servus eggs, as well as nonparasitized stink bug (Acrosternum hilare, E. servus, Murgantia histrionica, and Podisus maculiventris) eggs, were examined using electron microscopy. Egg response to perforation by a tungsten probe served as a control. Microscopy images depicted the chorion surface as characterized by a matrix of ridges and micropylar processes in a ring around the margin of the operculum. Observations of oviposition sites showed a “scab” formed where the ovipositor penetrated the chorion, and at sites penetrated by the probe. These formations appeared to be the result of fluids from inside the egg leaking out, drying, and hardening after oviposition or probe perforation, suggesting that the response was not due to substances secreted by the parasitoid. Further, no open wounds or holes were seen to increase the possibility of insecticides entering parasitized eggs.

Green Stink Bug, Acrosternum hilare (Say) (Insecta: Hemiptera: Pentatomidae)

EENY-431, a 5-page illustrated fact sheet by Celina Gomez and Russell F. Mizell III, is part of the Featured Creatures collection. It describes this commonly encountered pest of seeds, grain, nuts, and fruit — its distribution, description, life cycle and biology, hosts, damage, and management. Includes selected references. Published by the UF Department of Entomology and Nematology, February 2009. EENY-431/IN794: Green Stink Bug, Chinavia hilaris (Say) (Insecta: Hemiptera: Pentatomidae) (ufl.edu)

Efficacy of Insecticides Against Acrosternum hilare and Euschistus servus (Hemiptera: Pentatomidae) in Virginia and North Carolina

Laboratory bioassays and field trials were conducted to evaluate the efficacy of selected organophosphate, pyrethroid, and neonicotinoid insecticides, as well as a chitin inhibitor, novaluron, against 2 common stink bug pests in Virginia, the green stink bug, Acrosternum hilare (Say), and the brown stink bug, Euschistus servus (Say). Green bean dip bioassays revealed differences in insecticide susceptibility between the 2 species. Acrosternum hilare adults were highly susceptible to all pyrethroids tested, the organophosphates except acephate, and the neonicotinoids except acetamiprid. Acrosternum hilare nymphs were also susceptible to all pyrethroids tested. In general, the neonicotinoids, dinotefuran and clothianidin, were toxic to A. hilare, whereas thiamethoxam and acetamiprid were toxic to E. servus. In field trials in soybean, the neonicotinoids, dinotefuran, imidacloprid, and thiamethoxam were efficacious at controlling stink bugs and, in general, performed comparably to the organophosphates and pyrethroids. These results indicate that neonicotinoid insecticides offer an alternative to growers for managing stink bugs that may fit with integrated pest management programs where conservation of natural enemies is a consideration.

Damage to Soybean by Acrosternum hilare (Say) (Heteroptera: Pentatomidae)

A series of field-cage experiments were conducted in 2002 and 2003 in southeast Arkansas to measure the impact of feeding by green stink bug, Acrosternum hilare (Say), on soybean yield and seed damage. Stink bugs were collected from local soybean fields and released in 1.8 × 1.8 × 1.8 m walk-in screen cages at densities of 0, 3, 9, and 18 bugs per row-m on maturity group (MG) IV and MG V soybean at different stages of crop phenological development. Damaged seed at harvest was significantly related to caged density of A. hilare in most of the cage experiments. Yield loss was associated with density of caged bugs in 7 of 11 different experiments and ranged from 13.4–60.5 kg/ha (0.2–0.9 bu/a) lost per bug per row-m. MG IV and MG V soybean were similarly impacted by density of A. hilare when exposed at the same stage of crop development. Feeding by small and large nymphs at early (R2–R3) and mid (R5–R6) reproductive stages resulted in significant yield loss. Feeding damage was apparent on late reproductive stage soybean (R7–R8), but no measurable impact on yield was observed. This suggested that thresholds could be raised or control efforts could be terminated for stink bugs infesting R7–R8 stage soybean. Damage due to feeding by stink bugs is related to various factors, but crop phenology, density of bugs, and length of infestation time are consistent and predictable influences that are interrelated, and all should be considered in determining the need to control field populations.

An Improved Trap for Monitoring Stink Bugs (Heteroptera: Pentatomidae) in Apple and Peach Orchards

Capture of stink bugs (Heteroptera: Pentatomidae) in apple orchards with yellow pyramid traps baited with Euschistus spp. (Heteroptera: Pentatomidae) aggregation pheromone, methyl (2E,4Z)-decadienoate, was 4 fold greater when traps were topped with a 3.8-L jar with a 1.6 cm diameter opening and trimmed wire edging than with a 1.9-L jar with a 5 cm diameter opening with no wire edging. Stink bug capture in the 3.8-L jar top was unaffected by the presence or size of an insecticide ear tag, indicating that this improved design led to increased captures by reducing escape. Sixty-four percent fewer stink bugs escaped from 3.8-L jar tops with the improved capture mechanism than from the 1.9-L jar tops. Green stink bug, Acrosternum hilare (Say), was more susceptible to the presence of the insecticide ear tag than the brown stink bug, Euschistus servus (Say), with dusky stink bug, E. tristigmus (Say), exhibiting high mortality in traps with and without ear tags. Among baited and unbaited pyramid traps with different visual stimuli, fewer captures were recorded in black pyramid traps than in clear, yellow, green or white pyramid traps. Similar numbers of brown stink bugs were captured in yellow pyramid traps deployed on the ground between trees or on horizontal branches within trees in the orchard border row. Captures of dusky and green stink bugs were greater in the tree pyramid, especially from August to mid-October. Relationships between stink bug capture and injury will need to be determined before this trap can be incorporated as a decision-making tool in pest management programs.