BackgroundCytoplasmic incompatibility (CI) is induced in nature by Wolbachia bacteria, resulting in conditional male sterility. Previous research demonstrated that the two Wolbachia strains (wAlbA and wAlbB) that naturally co-infect the disease vector mosquito Aedes albopictus (Asian tiger mosquito) can be replaced with the wPip Wolbachia strain from Culex pipiens. Since Wolbachia-based vector control strategies depend upon the strength and consistency of CI, a greater understanding is needed on the CI relationships between wPip, wAlbA and wAlbB Wolbachia in Ae. albopictus.MethodsThis work consisted of a collaborative series of crosses carried out in Italy and in US to study the CI relationships between the “wPip” infected Ae. albopictus strain (ARwP) and the superinfected SR strain. The Ae. albopictus strains used in Italian tests are the wPip infected ARwP strain (ARwPIT), the superinfected SR strain and the aposymbiotic AR strain. To understand the observed pattern of CI, crossing experiments carried out in USA focused on the study of the CI relationships between ARwP (ARwPUS) and artificially-generated single infected lines, in specific HTA and HTB, harbouring only wAlbA and wAlbB Wolbachia respectively.ResultsThe paper reports an unusual pattern of CI observed in crossing experiments between ARwP and SR lines. Specifically, ARwP males are able to induce full sterility in wild type females throughout most of their lifetime, while crosses between SR males and ARwP females become partially fertile with male aging. We demonstrated that the observed decrease in CI penetrance with SR male age, is related to the previously described decrease in Wolbachia density, in particular of the wAlbA strain, occurring in aged superinfected males.ConclusionsThe results here reported support the use of the ARwP Ae. albopictus line as source of “ready-made sterile males”, as an alternative to gamma radiation sterilized males, for autocidal suppression strategies against the Asian tiger mosquito. In addition, the age dependent CI weakening observed in the crosses between SR males and ARwP females simplifies the downstream efforts to preserve the genetic variability within the laboratory ARwP colonies, to date based on the antibiotic treatment of wild captured superinfected mosquitoes, also reducing the costs.

Control of cucurbit pests, such as striped cucumber beetle (Acalymma vittatum), spotted cucumber beetle (Diabrotica undecimpunctata howardi) and squash bug (Anasa tristis), in organic systems is difficult due to a lack of effective insecticide options. This has led to the development of many integrated pest management techniques, such as use of row covers, crop rotation and cover crops. This study explored the novel use of strip tillage and row covers to reduce pest pressure in summer squash (Cucurbita pepe) and muskmelon (Cucumis melo) production systems. Results showed that although strip tillage reduced striped cucumber beetle and squash bug numbers, there was a yield reduction in both crops compared with the plasticulture system. Row cover increased marketable yield in both systems, with the highest yield being in the plasticulture system. Unmarketable fruit directly attributed to insect damage was higher in the plasticulture systems, but was not significantly different when compared with the strip tillage system. Although there are many documented positive attributes of strip tillage, results from this study indicate that a combination of plasticulture and row cover may be a superior system for organic cucurbit production.

Concerns about global pollinator declines have placed a growing focus on understanding the impact of agriculture practices on valuable native pollinators in these systems. Cultivation practices such as tillage disturb agroecosystems and can have negative impacts on ground-nesting pollinators. The squash bee, Peponapis pruinosa (Say), is a ground-nesting specialist pollinator of Cucurbita (Cucurbitaceae) crops (i.e., pumpkins and squash) that often nests in agricultural fields and thus may be vulnerable to these practices. We investigated the impact of tillage on nesting behavior of P. pruinosa in plasticulture and strip-tilled squash systems. We used choice experiments to test nesting substrate preference and nesting success of caged P. pruinosa in two soil tillage systems: strip tillage and plasticulture. The strip tillage system comprised two tillage zones (strip-tilled row with no-till edges), and the plasticulture system comprised two tillage zones (plastic bed and conventional tillage edge). The results of our study indicate that P. pruinosa nesting density did not significantly differ between the strip tillage and plasticulture systems. Within each system, P. pruinosa preferred excavating nests in the most disturbed soil zones (strip-tilled row and conventionally tilled edge). In the strip tillage system, the strip-tilled row had significantly more nests than the no-till edge. Results of these studies suggest that soil tillage practices can influence P. pruinosa nesting choice and production practices should be considered when developing a pollinator protection plan.

Pest management in cucurbit (Cucurbitaceae) cropping systems is challenging. As a result, pesticides are heavily used for managing insect pests and diseases. This work focused on the application of integrated pest management (IPM) techniques to control pests and reduce reliance on insecticide sprays while maintaining the quality and quantity of marketable yields in two commonly grown cucurbit crops: muskmelon (Cucumis melo) and summer squash (Cucurbita pepo). Plasticulture (raised beds covered in black plastic mulch) and strip tillage, two soil management systems commonly used for cucurbit IPM production, were compared to determine their impact on yield and pest numbers during the 2013–14 growing seasons. Additionally, the use of early season rowcovers and their impact on yield and pest pressure were investigated. Plasticulture use increased marketable yields compared with strip tillage for both summer squash and muskmelon, but strip tillage resulted in fewer total pests for both crops. Rowcover use did not have a consistent effect on insect pest numbers and showed a negative impact on the yield of both summer squash and muskmelon. No significant impacts on yield were observed when the interaction between rowcovers and the tillage system was investigated. The use of rowcovers impacted pest numbers, but these impacts were not consistent between insect pest species. Insecticide use was reduced in covered treatments, but only by one application. We concluded that these management techniques have the potential to be used in an IPM system, but the reduced marketable yield of strip tillage systems may reduce the adoption of this IPM technique for these crops.

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