Alternative methods of pest control can and should be encouraged, especially those that consider the reality of smallholder family farmers. Here, we evaluated the potential of Agave americana (agave) extracts for the control of the aphid Brevicoryne brassicae in cabbage (Brassica oleracea L. var acephala) in the field and laboratory. The field experiments consisted of the evaluation of the proportion of dead aphids on cabbage plants after application of agave extracts. In the field, agave mixed with cow milk caused mortality above 80% and was the most effective extract. Agave mixed with water and agave mixed with ethanol elicited mortality above 60%. In the laboratory, we evaluated the mortality of aphids after the application of different concentrations of aqueous agave extracts; the commercial insecticide deltamethrin was included as positive control. Evaluation took place at 3, 6, 12, 24, 48 and 72 hr after applying the treatment. As expected, deltamethrin was the most effective treatment. However, agave extract at concentrations of 0.750 and 0.500 g/mL caused >70% mortality 3 hr after application. We conclude that A. americana extracts decreased aphid populations and is a promising alternative to the commercial insecticide against aphids in cabbage. K E Y W O R D S agave, aphids, biopesticides, horticulture, plant extracts
The fall armyworm (FAW) Spodoptera frugiperda is the most significant lepidopteran corn pest in South American countries. Transgenic Bt corn, producing the Cry1Fa toxins, has been used to control this pest, but there is clear evidence that some FAW populations have developed resistance. To determine if there are costs associated with resistance, we compared the mass of adults, the duration of mating, and the mass of the first spermatophore produced, as well as the lifetime fecundity and fertility of once-mated susceptible (SS) and resistant (RR) females. Adult mass was affected by both sex and strain, with SS females being significantly larger than RR ones, while the inverse was true for males. RR pairs took significantly longer to mate than SS pairs, yet the mass of spermatophores produced by RR males was significantly less than those of SS males. The total number of eggs laid did not differ but the fertility of eggs from once-mated RR pairs was significantly lower than that of SS pairs. Our data provided clear evidence that the development of Bt resistance affected the reproductive capacity of resistant FAW.
Lepidopteran male mating success is recognized to be directly related to physical and behavioural traits such as ability, vigour, activity and persistence in courtship. In the tomato fruit borer Neoleucinodes elegantalis Guenée, the mating system is known to be monogamic and therefore males' sexual investment is apparently low. The hypothesis that recently mated males have a remating probability equal to that of virgin males is tested. The impact of body size in remating success and the cost of remating are also analyzed. Mated males show as much propensity to remate as naïve ones. Copula duration and the time taken to copulate are similar in mated and virgin males. However, spermatophore size is not related to male size. The results suggest the ability of N. elegantalis males to remate within 24 h between mating events and their propensity to remate are not affected by copula investment.
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