A Laboratory Bioassay Method to Assess the Use of Toxic Bait on Anastrepha fraterculus (Weidemann 1830).

The lack of standardization of bioassays for the evaluation of toxic bait toxicity on the South American fruit fly, Anastrepha fraterculus (Weidemann 1830), has led to erroneous interpretations of assay results. The objective of this study was to develop a methodology for the standardization and validation of toxicological tests on A. fraterculus toxic bait using the Success™ 0.02CB formulation (80 mg L-1 of spinosad). Anastrepha fraterculus adults, obtained from larvae reared on an artificial diet, showed higher susceptibility (LT50 = 48.96 h) than adults from larvae reared on cattley guava (LT50 = 53.83 h) and mango fruit (LT50 = 53.55 h). Anastrepha fraterculus adults at the age of five (LT50 = 65.30 h), 15 (LT50 = 59.01 h), and 30 (LT50 = 55.53 h) days presented similar toxicity. The consumption of toxic bait (4.74 mg) increased at 15 days, a fact also observed with insects without food deprivation. In addition, the absence of a food source (artificial diet) with the toxic bait significantly reduced adult mortality time by 7 h (LT50 = 57.42 h). In relation to exposure time, adults exposed to toxic bait for 1 h reduced consumption by 25%; however, they showed the same susceptibility as insects exposed to 2 (LT50 = 55.72 h), 4 (LT50 = 57.64 h), and 8 h (LT50 = 57.76 h). However, with 24 h of food deprivation, they had a higher susceptibility (LT50 = 46.48 h). Five-day-old A. fraterculus adults fed an artificial diet before being deprived of food for 12 or 24 h, then exposed to toxic bait for 4 h in the absence of a food source, are considered optimum conditions to evaluate the toxicity of toxic bait.

A rumen unprotected conjugated linoleic acid supplement inhibits milk fat synthesis and improves energy balance in lactating goats.

Feeding trans-10, cis-12 CLA supplements in a rumen-protected form has been shown to cause milk fat depression (MFD) in cows, ewes, and goats. Methyl esters of CLA were shown to be as effective as FFA in inducing MFD when infused postruminally, but their efficacy as a feed supplement has not been addressed in studies with lactating ruminants. In the present study, we investigated the effects of an unprotected trans-10, cis-12 CLA supplement as methyl esters on performance, milk composition, and energy status of dairy goats. Eighteen multiparous Toggenburg goats were randomly assigned to dietary treatments in a crossover experimental design (14 d treatment periods separated by a 7 d washout interval): 30 g/d of calcium salts of fatty acids (Control) or 30 g/d of a rumen unprotected CLA supplement containing 29.9% of trans-10, cis-12 CLA as methyl esters (CLA). Lipid supplements were mixed into a concentrate and fed individually to animals 3 times a day as a total mixed ration component. The DMI, milk yield, milk protein and lactose content and secretion, and somatic cell count were unaffected by CLA treatment. On the other hand, milk fat content and yield were reduced by 19.9 and 17.9% in CLA-fed goats. Reduced milk fat yield in CLA-fed goats was a consequence of a lower secretion of both preformed and de novo synthesized fatty acids. The CLA treatment also changed the milk fatty acid profile, which included a reduction in the concentration of SFA (2.5%), increased MUFA and PUFA (5.6 and 5.4%, respectively), and a pronounced increase (1576%) in milk fat trans-10, cis-12 CLA. Consistent with the high milk fat trans-10, cis-12 CLA content, all desaturase indexes were reduced in milk fat from CLA-fed goats. The MFD induced by CLA reduced the energy required for milk production by 22%, which was accompanied by an improvement in the estimated energy balance (P < 0.001), greater blood glucose concentration (P < 0.05), and a trend for increased BW (P = 0.08). Approximately 7.2% of trans-10, cis-12 CLA was estimated to escape from rumen biohydrogenation and indirect comparisons with data obtained from other studies suggest equivalent MFD between dietary CLA in the methyl ester form and rumen protected sources. Thus, despite the apparent low degree of rumen protection, our results suggest that methyl esters of CLA could be an alternative to rumen protected CLA supplements due to manufacturing and cost advantages.