P. S. Shera

Effect of mating combinations on the host parasitisation and sex allocation in solitary endoparasitoid, Aenasius arizonensis (Hymenoptera: Encyrtidae)

ABSTRACT Aenasius arizonensis (Girault) is an important solitary endoparasitoid of Phenacoccus solenopsis Tinsley. To optimise the mass production of high-quality females, it is important to assess the influence of mating regimes on the progeny fitness and sex allocation. We, therefore, hypothesise that mating combinations in A. arizonensis adults emerged from different host instars may influence parasitism and sex allocation in the subsequent generation. Therefore, we compared three nymphal instars (1st, 2nd and 3rd) and adults host stages of P. solenopsis for parasitism and sex allocation by A. arizonensis. Further, F1 female progeny of the parasitoid emerged from different host instars was henceforth evaluated for its fitness in six mating combinations. A. arizonensis females parasitised all the host stages except the 1st instar nymphs. The parasitised 2nd instar nymphs yielded only males, while the sex ratio in the later host instars was strongly female-biased. The parasitoid females preferred 3rd instar nymphs with respect to higher parasitism (74.0–84.0%) and produced more females in the F1 progeny as compared to other host stages. F1 females that emerged from 3rd instar nymphs produced significantly higher parasitism (74.0–79.0%). These mating combinations also yielded more female progeny in the F2 generation. However, parasitism by F1 females was significantly lower (9.0–12.0%) when mated with males that emerged from 2nd instar P. solenopsis nymphs. Moreover, latter combinations yielded only male progeny in F2 generation. These findings can be used in laboratory mass rearing of this parasitoid vis-à-vis biological control of P. solenopsis.

Suitability of different mealybug species as hosts to solitary endoparasitoid, Aenasius arizonensis (Girault) ( = Aenasius bambawalei Hayat)

ABSTRACT We investigated the suitability of six mealybug species, namely Phenacoccus solenopsis, Saccharicoccus sacchari, Paracoccus marginatus, Drosicha mangiferae, Nipaecoccus viridis and Ferrisia virgata as hosts to Aenasius arizonensis ( = Aenasius bambawalei). The study was conducted to ascertain a viable parasitic relationship between a parasitoid species and different mealybug hosts. Successful parasitization, complete development of immature stages within the host and adult emergence was observed only in P. solenopsis, whereas, other mealybug species were not found suitable as hosts by the parasitoid in both choice and no-choice tests. The development studies of A. arizonensis on P. solenopsis showed that the mean duration from oviposition to mummy formation was 6.13 days, while, from mummy formation to adult emergence, it was 5.43 and 7.05 days for male and female, respectively. The total development period from oviposition to adult emergence was 11.28 days for males and 13.13 days for females. Female adults (19.96 days) live longer as compared to male adults (7.83 days). Among different mealybug species, P. solenopsis was observed to be the only ecological and fundamental host of A. arizonensis.

Genetic Improvement of Biocontrol Agents for Sustainable Pest Management

Genetic improvement involves directed purposeful genetic alterations to enhance the efficacy of natural enemies for biological control. This may be achieved by conventional approaches as well as through recombinant DNA techniques. The conventional methods include strain selection, serial passage through hosts, mutation, conjugation, transduction, selective breeding, hybridisation, etc., whereas the genetic engineering approaches involve gene transfer utilising various methods. Entomophagous insects may be improved for climatic tolerance, sex ratio, host-finding ability, host preference, increased host range, increased pesticide resistance, etc. The main objectives in genetically altering microbes are to increase host range, virulence and persistence. The cry genes from Bacillus thuringiensis have been cloned and expressed in a wide variety of organisms (baculoviruses to cyanobacteria) as well as in plants in attempts to improve their delivery and efficacy against insect pests. Apart from B. thuringiensis, binary toxin from different B. sphaericus strains has been expressed in different hosts like Escherichia coli, non- or low-toxic B. sphaericus and crystal minus Bt israelensis as well as in Caulobacter crescentus or cyanobacteria Anabaena sp. Insect viruses, especially baculoviruses, are mostly specific viruses which can replicate only in hosts. The recombinant DNA technology has its current applications in inserting foreign genes into insect baculoviruses and achieving their rapid and efficient expression in the recipient host systems. Candidate genes for hyperexpression in the baculoviruses include those encoding insect-specific enzyme genes (juvenile hormone esterase gene), hormone genes (eclosion hormone gene, diuretic hormone gene) and insect-specific foreign toxic genes (scorpion venom toxin genes, predatory mite toxin gene, predatory spider toxin gene, parasitic wasp venom gene and Bt δ-endotoxin genes). It is worthwhile to mention that genetic engineering of BCAs is potentially very promising and has led to the development of more effective entomopathogens with desired pathogenicity, virulence, broad host range and persistence, providing a valuable tool for sustainable pest management.