Interactions of brown marmorated stink bug, Colletotrichum acutatum and trap crops in organic tomato production

Colletotrichum spp. (Ascomycota) cause anthracnose of tomato fruits (Solanum lycopersicum). Halyomorpha halys, the Brown Marmorated Stink Bug (Hemiptera: Pentatomidae) is an invasive insect that injures tomato fruits with a piercing/sucking mouthpart. To determine if H. halys feeding increases incidence of anthracnose on tomato fruit, five experiments were conducted. A 21-day transmission study was performed using detached fruits inside plastic containers in an incubator at 22°C. Tomato fruits receiving stink bugs with Colletotrichum inoculum had significantly higher anthracnose incidence than fruit receiving Colletotrichum inoculum only. A treatment using infested stink bugs (H. halys was placed in a petri dish of sporulating C. acutatum for 24h) to assess transmission had significantly higher anthracnose incidence than the sterilized water control. In a stink bug wounding treatment (H. halys was placed in the container with tomato fruits for 7 days, removed, and Colletotrichum inoculum was sprayed), anthracnose incidence was significantly less than in a stink bugs + inoculum treatment at 10 and 17 days, but these treatments did not differ at 21 days. A whole plant study was performed inside insect rearing and observation cages for 17 days. Anthracnose incidence on fruits of plants with stink bugs + inoculum was significantly greater than on all other treatments. Anthracnose incidence in the stink bug transmission and inoculum only treatments was significantly greater than with water controls or stink bug only treatments. In a field experiment using whole plants, 0, 1, 3, and 9 H. halys nymphs were added to mesh sleeves fitted around tomato fruit clusters for periods of 5 and 10 days. Number of stink bugs explains more of the variation (P<0.001) in Colletotrichum incidence than days in sleeve (P=0.1095). The two-way interaction between the days in sleeve and stink bug number was not significant (P=0.6627). When averaged across days in sleeve, anthracnose incidence was higher in treatments with nine stink bugs than treatments with zero, one, or three stink bugs (P<0.10). Fungi were isolated from H. halys fed on infected tomatoes in the lab. Stylets and legs were cultured on Yeast extract/sucrose agar to isolate colonies of C. acutatum. C. acutatum was recovered from either leg or stylet of 37.5% of insects feeding on infected fruit but not from control groups. A large scale field study was conducted in 2013 to evaluate whether insect feeding scars on tomato fruits were correlated with presence of Colletotrichum spp. Trap crops of sunflower and corn were established around tomatoes to deter insect feeding on tomatoes. Visual sampling for H. halys and other pentatomids was performed weekly. The field trials were repeated in 2014, however only sunflower was evaluated as a trap crop in 2014. H. halys populations were low in both seasons. No significant differences in H. halys population densities were found between trap crop treatments in 2013. Feeding scars were positively correlated with anthracnose incidence (R=0.2385) across both (sunflower and control) treatment groups in both seasons (p<0.0001). This trend was consistent in sweet corn trap crop plots in 2013 as well (p<0.018). These results support the hypothesis that H. halys contributes to the spread of anthracnose caused by C. acutatum in tomato by wounding and by phoretically carrying propagules from inoculum sources to susceptible hosts