Possible causes of spatial variability inDiatraea saccharalisFabr. (Lep., Crambidae) and its parasitoid populations in sugarcane fields in Brazil

Abstract

Based on the large data set stored in some sugarcane mills regarding the biological control programme of Diatraea saccharalis using the parasitoids Cotesia flavipes and tachinid flies, the aim of the present study was to determine whether sugarcane varieties, number of cuts and plant ages are major determinants in promoting spatial variability in D. saccharalis, C. flavipes and tachinid fly populations in sugarcane fields in the state of Sa˜o Paulo (Brazil). The data set used to support this study was provided by the Sa˜o Joa˜o and Barra sugarcane mills. Coefficient of variation was adopted as a measure of the spatial variability of population density. Spatial variability was estimated for the total density of D. saccharalis (parasitized + unparasitized larvae), and also for D. saccharalis larvae parasitized by tachinids and by C. flavipes. Statistical analysis revealed that the spatial variation in D. saccharalis populations was influenced by the number of cuts and by plant ages in the Barra and Sa˜o Joa˜o Mills, respectively. Similar results were obtained for D. saccharalis larvae parasitized by tachinids; however, in the Sa˜o Joa˜o Mill, the spatial variability of these populations was also influenced by the different number of varieties. Finally, considering D. saccharalis larvae parasitized by C. flavipes, no significant regressions with any of the three categories were observed for both sugarcane mills. The multitrophic implications for this agricultural system are also discussed.

Exposure to sugarcane borer‐induced plant volatile (E)‐caryophyllene enhances parasitoid recruitment

“…Various other strategies, including manual removal, development of Bt sugarcane plants (Arencibia et al, 1999), and biological control (Parra, 2014) have been combined in integrated pest management strategies. The main biological control agent for D. saccharalis is the gregarious larval endoparasitoid and cenobiont wasp, Cotesia flavipes (Cameron) (Hymenoptera: Braconidae) (Rossi, 2003), which is an endoparasitoid of lepidopterous stem borers in various Poaceae crops such as sugarcane, maize, sorghum, and other perennial grasses (Nagarkatti & Nair, 1973). Females oviposit into the hemocoel of borers and alter host physiology with venom and polydnaviruses that reduce host immunity, thus allowing larval development (Scaglia et al, 2005).…”

“…3.3 million ha of sugarcane (Parra, 2014). Release of C. flavipes has been shown to keep D. saccharalis infestation at a level of 2-3% (Botelho & Macedo, 2002;Rossi, 2003), which is assumed to be sufficient to keep damage below the economic threshold.…”