14 



wingless condition, they would not be likely to stray far away 

 from their birth place. This however was not the case, for just 

 as the parasite reaches its maximum in numbers, at the same 

 time as the hopper, so do the hyperparasites at the same time as 

 tlie parasite. When the Pseudogonatopus was at its greaest 

 numbers, the hyperparasites were noticed in the field in con- 

 siderably greater numbers still. Of course it must also be re- 

 membered that in many cases the destruction done by the Dryi- 

 nid parasite is supplemented by the work of other parasitic or 

 predaceous insects. With the most successful hoppers (by which 

 I mean those, which are most numerous in individuals), it would 

 appear that at their numerical maximum, they exhibit signs of 

 becoming a highly destructive pest, but just at this point (at 

 any rate in normal seasons), they suddenly,/ owing to the attacks 

 of parasites or predators, fall away to about their numerical 

 nnnimum. 



To take another instance, a common species of Sipliaiifa was 

 observed in numbers in Northern Queensland in various locali- 

 ties, but not so numerously as a rule as to be considered injuri- 

 ous to any considerable extent. On the other hand, under un- 

 natural conditions, it showed itself capable of doing the greatest 

 damage, for an isolated colony established on a bush in the town 

 of Cairns where its natural enemies had little chance of finding 

 it, had so injured the bush that the owner cut away and destroy- 

 ed a large portion of it. At Townsville, on an isolated row of 

 trees, the same species had evidently increased to great num- 

 bers prior to our visit, as could be easily seen by the appearance 

 of the affected trees, and the empty larval skins of the Siphanta. 

 In this case, however, the parasites had already discovered their 

 prey, and we saw few of the latter, but the cocoons, mostly 

 empty, of a Ncodryinns were so numerous, that as many as 32 

 v;ere picked off a single fig-leaf! Egg parasites were also at 

 work on the few patches of eggs that we found. Indeed in most 

 cases, it will no doubt be found that the work of the Dryinidae, 

 admirable as it is, to a greater or less extent is supplemented by 

 that of other predaceous and parasitic insects. In fighting a leaf- 

 liopper pest by the importation of parasites or predators, it will 

 no doubt be generally found necessary to make a selection of 

 carefully chosen enemies rather than to rely on a single specific 

 enemy, though the latter might in some cases be perfectlv suc- 

 cessful, provided its hyperparasites be carefully excluded and 

 tliat none likely to attack it already exist in the country to 

 Vvhich it is imported. 



