RESUMO
The pink hibiscus mealybug Maconellicoccus hirsutus (Hemiptera: Pseudococcidae) is an invasive pest of an enormous variety of crops and has become a concern in many parts of the world. Early attempts to control M. hirsutus with chemical insecticides and cultural methods have failed due to the cryptic habit of the insect. We assessed the entomopathogenic nematode Heterorhabditis amazonensis as a biological agent against different insect stages. Comparing different concentrations of the nematode, insect females were very susceptible, with more than 90% of the insects killed. In second and third nymphal stages mortality rates varied from 20 to 60% depending on the nematode concentration. The first nymphal stage as much less susceptible to nematodes due to their small size. The number of nematodes capable of invading the insect host did not vary between the different concentrations. However, the LC50 for females (35.2 IJ/insect), second and third nymphal stages (83.9 IJ/insect) demonstrated that H. amazonensis should be considered as a potential biocontrol agent of the pink hibiscus mealybug.The pink hibiscus mealybug Maconellicoccus hirsutus (Hemiptera: Pseudococcidae) is an invasive pest of an enormous variety of crops and has become a concern in many parts of the world. Early attempts to control M. hirsutus with chemical insecticides and cultural methods have failed due to the cryptic habit of the insect. We assessed the entomopathogenic nematode Heterorhabditis amazonensis as a biological agent against different insect stages. Comparing different concentrations of the nematode, insect females were very susceptible, with more than 90% of the insects killed. In second and third nymphal stages mortality rates varied from 20 to 60% depending on the nematode concentration. The first nymphal stage as much less susceptible to nematodes due to their small size. The number of nematodes capable of invading the insect host did not vary between the different concentrations. However, the LC50 for females (35.2 IJ/insect), second and third nymphal stages (83.9 IJ/insect) demonstrated that H. amazonensis should be considered as a potential biocontrol agent of the pink hibiscus mealybug.
RESUMO
The life cycle of four Steinernema species was observed in 4 insect micro-insect host species (less than 5mm long). Several parameters were measured: sex ratio of invading nematodes, percentages of host infection and offspring production, penetration rate of infective juveniles per insect and number of new generation of infective juveniles. All parameters varied among nematode species, micro-host species and application rates. All Steinernema species were capable to invade micro-insect hosts, however, invasion decreased as insect size decreased and as nematode species size increased. None of the nematode species achieved 100% mortality in the micro-hosts. Due to size differences in the nematode species, Steinernema glaseri was less capable of completing its life cycle and unable to invade smaller hosts whereas S. riobrave completed its life cycle in smaller hosts more frequently. The number of invading nematodes and the number of offspring produced had the same levels regardless of the nematode application rates, those results showed a maximum top in the number of individuals per micro-insect host. The offspring production in thrips species was only possible by endotokia matricida in S. riobrave. The sex of the invader nematodes also impeded the life cycle of S. affine because males colonized the entire body of the micro-insect host leaving no room for female invasion. The size of the host plays an irrefutable role in limiting the development of nematodes and it appears improbable that an entomopathogenic nematode population can persist in the soil without the presence of bigger insects.