Sumio Tojo

Involvement of both granular cells and plasmatocytes in phagocytic reactions in the greater wax moth, Galleria mellonella.

Although it has been previously found by most authors that only plasmatocytes are involved in phagocytosis of non-self in the greater wax moth, Galleria mellonella, in the present study we demonstrate that in vitro, both granular cells and plasmatocytes are involved in this reaction, using monolayers of these haemocytes prepared from larval haemolymph by a differential cell fractionation method. The adhesion of granular cells to glassware and phagocytosis by granular cells of FITC-labelled silica beads were both greatly reduced by the presence of p-NPGB, a serine proteinase inhibitor, which is known to inhibit the activation of the prophenoloxidase cascade, but the reactions were only partly influenced by PTU, an inhibitor of phenoloxidase. These results suggest that an enhancing factor for both reactions is phenoloxidase itself or a component induced during the course of activation of the prophenoloxidase cascade, but not the melanised substance produced by the action of this reaction. For plasmatocytes, attachment to non-self was totally blocked by the absence of CaCl(2) or by the presence of EDTA at concentrations greater than 20 mM, and phagocytosis was greatly enhanced by CaCl(2), but suppressed by EDTA. These results suggest that calcium is a factor required for adhesion of plasmatocytes, and that it also functions to enhance their phagocytic action.

Hormonal control of storage protein synthesis and uptake by the fat body in the silkworm, Bombyx mori

Abstract The female silkworm, Bombyx mori , rapidly accumulates two storage proteins, that are synthesized by the fat body, in the haemolymph during the feeding stage of the last-larval instar, and then sequesters them from the haemolymph into fat body during the larval-pupal transformation. The rapid synthesis and uptake of storage proteins by the fat body are shown to be induced by allatectomy in the early-penultimate larval instar. A juvenile hormone analogue, methoprene, is highly effective in inhibiting the allatectomy-induced synthesis, and, in a higher dosage, further blocks the uptake. Allatectomy in the late-penultimate larval instar shortly before moulting does not enhance the storage protein synthesis, but causes the uptake to occur two days earlier in the last-larval instar. Injection of 20-hydroxyecdysone is not stimulatory for synthesis of the proteins, but is effective to induce their uptake. Starvation during the early last-larval instar completely blocks the synthesis. From these results, it is suggested that storage protein synthesis is induced in the absence of juvenile hormone by some supplementary stimulus, possibly the supply of nutrient after feeding, and uptake is induced by ecdysteroids after a decline in the juvenile hormone level.

Effects of juvenile hormone and rearing density on wing dimorphism and oöcyte development in the brown planthopper, Nilaparvata lugens

Abstract The brown planthopper, Nilaparvata lugens , shows density-dependent wing dimorphism. By changing the rearing density of different nymphal stages the sensitive periods for wing-form determination were shown to be in the 2nd, 3rd and 4th instars. The 4th (penultimate) instar was most sensitive to a decrease of density which induced brachypterous forms. Juvenile hormones I and II and the analogue methoprene were shown to increase the proportion of brachypters when topically applied to female nymphs near the penultimate instar (0.3 mg live weight). Methoprene was also shown to stimulate vitellogenesis in (presumptive) macropters, which usually initiated the process about 24 h later than brachypters. This effect could be achieved by topical application to either the early final instar nymphs or to the adults 36–48 h after emergence. These results suggest that higher titre of juvenile hormone in the penultimate nymphal instar induces the development of brachypteous wings, and that a high titre in the final nymphal instar and an earlier elevation of the titre in the adult stage cause more rapid development of ovaries in the brachypters.

A report of progressive provisioning in a stink bug,Parastrachia japonensis (Hemiptera: Cydnidae)

The majority (75%) of femaleParastrachia japonensis (Hemiptera: Cydnidae), while caring for 1st and 2nd instar nymphs, foraged for and provisioned nests with drupes of the host plant,Schoepfia jasminodora (Olacacae), which the young then fed on. The maximum number of drupes found in a given nest was 27. Females could travel as fast as 61.4 cm/min while carrying drupes that were nearly double their weight, and were directly observed to travel as far as 10 m when encumbered with a drupe. It was found that nests which were far from the food source were provisioned with at least as many drupes as those nests that were within the drupe range. While females could not distinguish their own eggs from others, apparently they could distinguish their own nests containing their nymphs. Eggs failed to survive in the absence of a female, however, a small number of nymphs reached adulthood even in the absence of a female when drupes were provided. This report represents the first direct observation of progressive provisioning by a phytophagous hemipteran under field conditions.

Hormonal regulation of phase polymorphism and storage-protein fluctuation in the common cutworm, Spodoptera litura

Abstract Three storage proteins are synthesised by Spodoptera litura last-instar larvae as detected by an antiserum against pupal fat body proteins. The putative pupal storage proteins 1 and 2, appear in the haemolymph of the last-instar larvae 36 h after ecdysis under crowded rearing conditions: they appear 1 day later in isolated conditions. The appearance of these proteins in the haemolymph is prevented by juvenile hormone treatment and enhanced by allatectomy. Injection of 20-hydroxyecdysone into ligatured larvae does not induce appearance of these 2 proteins. Accumulation of protein 3 that reacts with Bombyx mori arylphorin antiserum is not blocked by juvenile hormone and is similar in both phases. It also accumulates to a small extent in the haemolymph during the moult to the final-larval instar and then disappears at ecdysis. One-hundred ng/ml ecdysteroid caused the sequestration of these proteins by the fat body, but a higher concentration of ecdysteroid (200 ng/ml) produced pupal cuticle in the isolated abdomens, suggesting that different ecdysteroid concentrations are necessary for these two events.

Immigration of the brown planthopper, Nilaparvata lugens, exhibiting various responses to density in relation to wing morphism

Considerable inherent variations in the relation between macropterous and brachypterous wing forms, and nymphal density were found in field populations of the brown planthopper, Nilaparvata lugens Stål (Homoptera: Delphacidae), collected from various locations in Japan. When compared under uniform laboratory rearing conditions, most of the female populations exhibited higher ratios of macropters with increasing nymphal density, but some showed extremely high proportion of brachypters and the others were highly macropterous, over broad ranges of density. These results indicate the possibility that the planthoppers in Japan, which are known not to persist in winter, are derived from different migration sources.

Enhancement of short wing formation and ovarian growth in the genetically defined macropterous strain of the brown planthopper, Nilaparvata lugens

When JH II, III or methoprene was applied in the nymphal stages to two different strains of the brown planthopper which were selected to produce long (macropterous) or short (brachypterous) wing forms, no effect was observed on the molting profile or metamorphosis. Brachypterization of a majority of the presumptive macropters was, however, observed by application of these chemicals, although there was no effect on wing form in the presumptive brachypters. The results show that the sensitive periods for the brachypterization of the presumptive macropters falls between early antepenultimate instar and within 1 or 2days of the penultimate instar, and that the chemicals were effective, in the following order of potency: methoprene>JH III>JH II. Ovarian growth was greatly enhanced in the presumptive macropters when JH III or methoprene was applied twice, within 12h of the 3rd or 4th nymphal instar and 6h before adult emergence. JH II on the other hand had no effect on ovarian growth when applied to the presumptive macropters at any of the nymphal stages. None of the chemicals had any effect on ovarian growth in the presumptive brachypters.

Suppression of the prophenoloxidase cascade in the larval haemolymph of the turnip moth, Agrotis segetum by an entomopathogenic nematode, Steinernema carpocapsae and its symbiotic bacterium

Abstract To study the suppression of the prophenoloxidase cascade in the larval haemolymph of the turnip moth, Agrotis segetum by Steinernema carpocapsae and its symbiotic bacterium Xenorhabdus nematophilus , living S. carpocapsae , heat-killed S. carpocapsae , living X. nematophilus , and heat-killed X. nematophilus were injected in four different treatments into final-instar larvae of A. segetum . In all of the treatments, the activation of prophenoloxidase cascade (initiated by laminarin in the insect haemolymph which was drawn 1 h after injection) was inhibited. This inhibition occurred in a dose-dependent manner. On the other hand, injection of non-pathogenic and fungus-feeding nematodes, Aphelenchus avenae did not induce a similar inhibition, and the nematodes were found to be entrapped in nodules within a melanized sheath. Co-injection of Aph. avenae with S. carpocapsae or X. nematophilus suppressed the prophenoloxidase cascade, while Aph. avenae survived in the haemolymph without being trapped by haemocytes. In all haemolymph of larvae into which foreign-bodies were injected, the levels of prophenoloxidase were essentially the same as those from control larvae, when determined by α-chymotrypsin treatment. These results indicate that S. carpocapsae and/or X. nematophilus suppress the prophenoloxidase cascade at an early step and also interfere with the role of haemocytes in self-defence.

Sensitive periods for wing development and precocious metamorphosis after precocene treatment of the brown planthopper, Nilaparvata lugens

The critical periods for juvenile hormone suppression of wing development and metamorphosis were examined in a pure brachypterous line of Nilaparvata lugens following topical application of Precocene II (PII) to various stages of the third and fourth nymphal stadia. When PII, in doses ranging from 10 pg to 100 ng, was applied to 12-h-old third or 6-h-old fourth stadium nymphs, long-wing formation (macroptery) was induced. Macropter induction ranged from 5 to 50% in females and from 30 to 50% in males, the effect being more prominent in males. The sensitive period for macropter induction lasted from the early second stadium through to day one of the fourth (penultimate) stadium. Beyond that period nymphs required sensitivity to PII and the numbers of macropters increased towards the final nymphal molt, again males were more sensitive. On the other hand, periods sensitive to PII for precocious metamorphosis induction appeared from early second stadium to 18 h after molting to the third nymphal stadium. Overlapping application of JH-III with PII at early third stadium could totally inhibit the occurrence of precocious metamorphosis and significantly rescue the macropter induction. From the data described, a scheme is presented for the control of wing development and metamorphosis by juvenile hormone, assuming two types of threshold value determining wing form and metamorphosis.

Provisioned Parastrachia japonensis (Hemiptera: Cydnidae) nymphs gain access to food and protection from predators

Females of the shield bug Parastrachia japonensis Scott progressively provision nymph-containing nests with drupes of the host tree, Schoepfia jasminodora (Olicaceae: Rosidae: Santales). The majority of nests are 5-15 m from the host tree, a distance thought to have been a major impetus for the occurrence of provisioning in this species. However, the function of provisioning is not well understood. We carried out two field experiments to determine whether provisioning is nutritionally important and whether it affords protection against predation. Development of nymphs was significantly delayed and their survival was low in the absence of provisioning, even when nests were within the area of ground on to which the drupes fell, apparently because of the poor quality of the majority of the drupes. Selective provisioning of good-quality drupes by female P. japonensis, a semelparous species, was thus necessary for young nymphs to obtain enough food for their development. Furthermore, even without a female in attendance, having drupes in the nest significantly reduced early mortality in the presence of a predator. Copyright 2000 The Association for the Study of Animal Behaviour.