Efficacy of enthomopathogenic fungus Metarhizium anisopliae against Tuta absoluta (Lepidoptera: Gelechiidae).

The tomato borer Tuta absoluta Meyrick is a serious tomato pest that has lately undergone a rapid expansion, causing severe crop losses. An integrated management is required to control this insect, within which biological control is now beginning to play a key role. In this regard, the effectiveness of a liquid formulation based on strains of the fungus Metarhizium anisopliae variety anisopliae (Metschnikoff) Sorokin (4.46 x 10(9) viable conidia per milliliter), applied together with irrigation water, has been evaluated by laboratory tests on different populations of T. absoluta. A bioassay method has been developed to test the efficacy of the product. The technique chosen has been validated and the different studied populations have been typified according to their susceptibility, determining the baseline susceptibility of the pest to the fungus. The results revealed a complete efficacy of M. anisopliae against pupae of T. absoluta at the recommended label rate (5.58 x 10(9) viable conidia per liter) for the populations assayed. Moreover, a notably lower dose was also sufficiently effective to control the tomato borer populations because values of LC90 lower than 3 x 10(9) viable conidia per liter were obtained unfailingly. The most sensitive populations were those collected in Almeria and Nijar, Spain, with LC50 values of 0.21 and 0.22 x 10(9) viable conidia per liter(-1), respectively. The average value obtained for LC50 was 0.34 x 10(9) viable conidia per liter(-1) and 2 x 10(9) for LC90. These results show the potential of M. anisopliae to control pupae of the tomato borer in integrated pest management programs.

Novel cytochrome P450 genes, CYP6EB1 and CYP6EC1, are over-expressed in acrinathrin-resistant Frankliniella occidentalis (Thysanoptera: Thripidae).

Control of Frankliniella occidentalis (Pergande) is a serious problem for agriculture all over the world because of the limited range of insecticides that are available. Insecticide resistance in F. occidentalis has been reported for all major insecticide groups. Our previous studies showed that cytochrome P450-mediated detoxification is a major mechanism responsible for insecticide resistance in this pest. Degenerate polymerase chain reaction was used to identify P450 genes that might be involved in acrinathrin resistance, in a laboratory population of F. occidentalis. Associated sequences were classified as belonging to the CYP4 and CYP6 families. Real-time quantitative polymerase chain reaction analyses revealed that two genes, CYP6EB1 and CYP6EC1, were over-expressed in adults and L2 larvae of the resistant population, when compared with the susceptible population, suggesting their possible involvement in resistance to acrinathrin.

Effect of biofumigation with manure amendments and repeated biosolarization on Fusarium densities in pepper crops.

In the region of Murcia (southeast Spain), sweet pepper has been grown as a monoculture in greenhouses for many years. Until 2005, when it was banned, soils were disinfested with methyl bromide (MB) to control pathogens and to prevent soil fatigue effects. The genus Fusarium plays an important role in the microbiological component associated with yield decline in pepper monocultures. In the present study, soils were treated with manure amendments, alone (biofumigation, B) or in combination with solarization (biosolarization, BS), with or without the addition of pepper plant residues. The B and BS treatments were compared with a treatment using MB. The extent of disinfestation was measured from the density of Fusarium spp. isolated from the soil before and after the respective treatments. Three different species were systematically isolated: Fusarium oxysporum, Fusarium solani and Fusarium equiseti. The repeated use of manure amendments with pepper crop residues, without solarization, was unable to decrease the Fusarium spp. density (which increased from 2,047.17 CFU g(-1) to 3,157.24 CFU g(-1) before and after soil disinfestation, respectively), unlike MB-treated soil (in which the fungi decreased from 481.39 CFU g(-1) to 23.98 CFU g(-1)). However, the effectiveness of the repeated application of BS in diminishing doses (with or without adding plant residues) on Fusarium populations (reductions greater than 72%) was similar to or even greater than the effect of MB.

Life-stage variation in insecticide resistance of the western flower thrips (Thysanoptera: Thripidae).

The life-stage variations in insecticide resistance of western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), to selective insecticides (acrinathrin, formetanate, and methiocarb) were studied using resistant laboratory strains. In each strain, the second-instar larva was less susceptible to the insecticides tested than the adults. The lower the resistance level of the adults, the higher the difference between larva and adult susceptibility: 32-fold to methiocarb, 15.4-fold to formetanate, and 180-fold to acrinathrin in the reference strain. In laboratory-selected resistant strains, these differences were much lower: 5.8-fold to methiocarb, 4.8-fold to formetanate, and 2.0-fold to acrinathrin. In selected strains, higher resistance levels for each insecticide were found, both for larvae and adults, compared with the reference strain. These results show that after insecticide resistance selection in adults, the resistance is carried over to the larvae, but at lower levels.

Carbamates synergize the toxicity of acrinathrin in resistant western flower thrips (Thysanoptera: Thripidae).

The insecticidal efficacy of mixtures of acrinathrin (pyrethroid) with carbamate fungicides (propamocarb, carbendazim, iprovalicarb, and diethofencarb) and insecticides (carbaryl, thiodicarb, pirimicarb, and oxamyl) was studied in a field strain of Frankliniella occidentalis (Pergande). The fungicide propamocarb and the insecticides pirimicarb and oxamyl were selected for further studies of their synergism action with more detailed bioassays. The method consisted of combining increasing concentrations of acrinathrin with a constant sublethal rate of the carbamate as synergist. These three carbamates did not show synergism to acrinathrin in a laboratory insecticide-susceptible strain, but they did in two field strains, with higher acrinathrin resistance corresponding to higher synergism. Carbamates such as pirimicarb, oxamyl, and propamocarb could be practical candidates for field use as synergists, even against other pests with metabolic resistance.

Impact of production system on development of insecticide resistance in Frankliniella occidentalis (Thysanoptera: Thripidae).

The western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), has become one of the most difficult insects to control in the intensive agriculture of southeastern Spain. However, resistance problems are quite different in two neighboring areas, Murcia and Almeria, with distinct production systems. Thirty-six field populations of western flower thrips from sweet pepper crops were collected in two different dates in Murcia and Almeria in 2005 and 2006. Western flower thrips populations collected were exposed to a diagnostic concentration of spinosad, methiocarb, acrinathrin, and formetanate. The results allowed the recognition of higher levels of resistance in Almeria compared with Murcia throughout the growing season. The mortality at the diagnostic concentration for spinosad (120 ppm) in western flower thrips populations ranged from 34 to 81% in Almeria, and from 73 to 100% in Murcia. The mortalities at the diagnostic concentration to acrinathrin (800 ppm) and formetanate (8000 ppm) were 17-31% in Almeria and 77-100% in Murcia, and 14-41% in Almeria and 48-99% in Murcia, respectively, indicating large geographic variations. Toxicity of methiocarb was higher for western flower thrips populations from both areas. However, mortality at the diagnostic concentration of methiocarb (2000 ppm) varied from 56 to 90% in Almeria, and it was from 94 to 100% in Murcia. The impact of production systems and agricultural practices of each area on the development and stability of insecticide resistance is discussed.

Lack of fitness costs of insecticide resistance in the western flower thrips (Thysanoptera: Thripidae).

The fitness costs of spinosad and acrinathrin resistance was investigated in the western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae). Fitness studies were conducted on susceptible and resistant strains of F. occidentalis. Resistant females were significantly more fecund (number of eggs per female) than susceptible females. The hatching rate (fertility) for both susceptible and acrinathrin-resistant strains was significantly lower than in the spinosad-resistant strain. Mean developmental time from egg to adult did not differ between thrips populations. Similarly, female longevity did not differ between populations. These data suggest that lack of fitness costs related to insecticide resistance may accelerate the development of insecticide resistance in populations of F. occidentalis from southeastern Spain.

Stability of spinosad resistance in Frankliniella occidentalis (Pergande) under laboratory conditions.

The stability of spinosad resistance in western flower thrips (WFT), Frankliniella occidentalis (Pergande), populations with differing initial frequencies of resistance was studied in laboratory conditions. The stability of resistance was assessed in bimonthly residual bioassays in five populations with initial frequencies of 100, 75, 50, 25 and 0% of resistant individuals. There were no consistent changes in susceptibility of the susceptible strain after eight months without insecticide pressure. In the resistant strain, very highly resistant to spinosad (RF50>23,000-fold), resistance was maintained up to eight months without further exposure to spinosad. In the absence of any immigration of susceptible genes into the population, resistance was stable. In the case of the population with different initial frequency of resistant thrips, spinosad resistance declined significantly two months later in the absence of selection pressure. With successive generations, these strains did not change significantly in sensitivity. Spinosad resistance in F. occidentalis declined significantly in the absence of selection pressure and the presence of susceptible WFT. These results suggest that spinosad resistance probably is unstable under field conditions, primarily due to the immigration of susceptible WFT. Factors influencing stability or reversion of spinosad resistance are discussed.

Genetics of spinosad resistance in Frankliniella occidentalis (Thysanoptera: Thripidae).

The genetic basis of spinosad resistance was investigated in the western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae). The resistant strain, selected in the laboratory for spinosad resistance from a pool of thrips populations collected in Almeria (southeastern Spain), showed a very high resistance to spinosad (356,547-fold based on LC50 values) compared with the laboratory susceptible strain. Mortality data from reciprocal crosses of resistant and susceptible thrips indicated that resistance was autosomal and not influenced by maternal effects. Analysis of probit lines from the parental strains and reciprocal crosses showed that resistance was expressed as an almost completely recessive trait. To determine the number of genes involved, a direct test of monogenic inheritance based on the backcrosses suggested that resistance to spinosad was probably controlled by one locus. Another approach, which was based on phenotypic variances, showed that nE, or the minimum number of freely segregating genetic factors for the resistant strain, equaled 0.59.