Sublethal effects of emamectin benzoate on life table parameters of the cotton leafworm, Spodoptera littoralis (Boisd.)

Background The cotton leafworm, Spodoptera littoralis (Boisd.), is a serious economic pest in Egypt. Pest control depends mainly on chemical control with several pesticides include conventional and modern insecticides. Comprehensive analysis of pesticides impacts needs to investigate sublethal effects in addition to lethal effect. Results In the current study, the leaf-dip bioassay method was used to evaluate emamectin benzoate (EMB) sublethal concentrations. Results showed that EMB proved high toxicity against S. littorals with LC50 value of 0.019 mg liter−1. Life table analysis showed that treatments with LC5 and LC15 prolonged larval period, mean longevity of males and females, mean generation time (T), doubling time (DT), adult preovipositional period (APOP), and total preovipositional period (TPOP) compared with control. On the contrary, net reproduction rates (R0), intrinsic rates of increase (r), finite rate (λ), fecundity, gross reproductive rate (GRR), and relative fitness were decreased compared to control. Conclusions The current study clarified that sublethal concentrations of EMB induce adverse effects and suppress the population growth of S. littorals. Our results would be useful to assess the overall effects of EMB on S. littorals and can contribute effectively in pest management.

Importance of Preovipositional Period of an Oligophagous Moth in Predicting Host Suitability

For oligophagous insects, larval performance is very important to evaluate host suitability in host use. However, key indices among all performance traits including survival, development, and fecundity of the adult insect to predict host suitability are not clear. To investigate the key performance indices, we observed the performance of an oligophagous moth Grapholita molesta (Busck) (Lepidoptera: Tortricidae), a pest mainly damaging rosaceous plants, on three apple varieties, three peach varieties, and three pear varieties in the laboratory by placing its eggs on fruits. The moth’s fitness was evaluated by the intrinsic rate of increase at fruit variety- and species-level variability. Our results showed that the preovipositional period of female moths and longevity of male moths were the indices primarily predicting intrinsic rates of increase for fruit variety and for fruit species. However, the preovipositional period of female moths was different at species-level variability but not at variety-level variability, whereas the longevity of male moths was not different at variety- or species-level variability. These results revealed that preovipositional period of female moths was a key predictor for host suitability in G. molesta. This study highlighted that gravid females may be a principal indicator in host resource optimization for oligophagous insects.

The Effect of Prey Density on Life Table Parameters of Hippodamia variegata (Coleoptera: Coccinellidae) Fed on Aphis gossypii (Hemiptera: Aphididae) under Laboratory Conditions

Life table gives the most comprehensive explanation of the survivorship, development, and reproduction of a population. The life table parameters of ladybeetle, Hippodamia variegata (Coleoptera: Coccinellidae), on different densities (20, 40, 60, 80, and 100) of third instar nymphs of Aphis gossypii were studied in a growth chamber (°C, % RH, and a photoperiod of 16L: 8D h). The adult preovipositional period and the total preovipositional period of female H. variegata were reduced as the prey density increased. The oviposition period was longer when prey density increased. Female longevity also increased significantly with increasing prey density. Fecundity was dependent on prey density. The lowest fecundity was obtained at density of 20 prey () and the highest at density of 100 ( eggs). Intrinsic rate of increase was dependent on prey density and ranged from to d−1 (female/female/day) with increasing prey density. Net reproductive rate and gross reproductive rate were also increased with increasing prey density. The peak reproductive values were dependent on prey density. However, mean generation time decreased as prey density increased. It was concluded that the increase in the density of A. gossypii nymphs had positive and significant effects on reproductive parameters of H. variegata.

Feeding and Ovipositional Responses of Adult Elm Leaf Beetle (Coleoptera: Chrysomelidae) to Simple and Complex Asian Elm Hybrid Selections

Nine recently developed simple and complex Asian hybrids with Ulmus davidiana, U. japonica, U. parvifolia, U. pumila, U. szechuanica and/or U. wilsoniana parentage were evaluated in no-choice laboratory bioassays for their suitability for the adult elm leaf beetle, Xanthogaleruca luteola (Müller). Suitability of each biotype was defined by the mean percentage of leaf tissue removed, the mean percentage of females ovipositing, and the mean number of eggs laid per female. Adult female beetles laid significantly more eggs on U. pumila (control) and the complex hybrid U. ‘Morton Red Tip’-Danada Charm™ indicating their greater suitability for ELB. The least suitable single and complex hybrids for adult elm leaf beetles as indicated by feeding and reproduction were U. davidiana x U. ‘ Morton’ -Accolade™ and U. szechuanica x U. japonica. Females feeding on more suitable elms oviposited 3 days earlier than females feeding on less suitable elms. Adult beetle fecundity was correlated with the length of the preovipositional period but mean percentage of females ovipositing was not correlated with length of the preovipositional period. Adult males and females lived approximately 4 days longer on the more suitable elms than on less suitable elms but adult longevity was not correlated with suitability. The percentage of leaf tissue removed by adult beetles on the different biotypes was correlated with beetle fecundity. Less suitable selections of U. davidiana x U. ‘ Morton’ -Accolade™ and U. szechuanica x U. japonica seem promising for future elm breeding programs.

Low Temperature Effects on Development, Mortality, Fecundity, and Viability of the Ectoparasitoid Catolaccus grandis (Hymenoptera: Pteromalidae)1

The low temperature threshold for development of Catolaccus grandis (Burks) was 12°C for eggs, 11.5°C for larvae, and 9.5°C for pupae. The developmental time for male or female parasitoids increased by 4.6 to 5.3 times and the preovipositional period of females increased from 2.2 to 9.3 days when the temperature was reduced from 30°C to 15°C. The number of degree-days to complete development was 225.6 for females and 197.2 for males. The mean duration of emergence for C. grandis ranged from 2.6 days at 27°C - 30°C to 5.7 days at 20°C. Reduction of the temperature from 25°C to 15°C increased the death rate of C. grandis 2.3 times and reduced emergence of parasitoid females by 77.8%. The percentage of emergence of females from pupae with the black thorax-yellow abdomen held at temperatures lower than 15°C for 20 days or more and pupae with yellow color held at 5°C for 10 or more days decreased significantly compared with females from pupae held at 25°C. Storage of pupae at 20°C or lower resulted in adult females with reduced fecundity. However, the sex ratio of the progeny was not significantly affected.