THE BLACK FLY OF CITRUS. 15 
take place, but which apparently do not become heavily infested 
with it; (3) supplemental food plants, or those which the adults may 
visit and from which they may obtain food, but on which either they 
do not lay eggs or, if they do, complete development does not take 
place. It must be borne in mind that these three classes are not 
clear-cut ones but merge into one another. They are based on the 
writers' observations in the Canal Zone. 
In this region the favorite food plants in the order named appear 
to be Ardisia revoluta, the oranges (both sweet and sour) , grapefruit, 
lemon, lime, and mango. No large areas of coffee in infested regions 
have been found in our surveys and little can be said about this host 
from our experience, though the writers in Cuba and Jamaica are 
agreed that it comes before mango in the list. 
Among the occasional hosts may be included such plants as sapo- 
dilla (Achras sapota), oil nut palm (Eleais melanococca) , Cashew apple 
(Anacardium occidentale) , sugar apple (Annona squamosa), Eugenia 
malaccensis, mamon (Melicocca bijuga), guava (Psidium guajava), 
and mamei (Lucuma mammosa) . With the exception of the favorite 
or preferred food plants these constitute an important means by 
which the insect may be spread on nursery stock or on individual 
plants. These occasional food plants may and probably will con- 
stitute an important source of reinfestation where control of the 
black fly, especially on citrus, is undertaken. This has been shown 
in the case of the oil nut palm {Eleais melanococca) under the heading 
"Spread of the insect," on pages 10-11. 
Among the supplemental food plants are the orange jessamine 
(Chalcas exotica), Barbados cherry (MalpigMa glabra), and crape 
myrtle (Lagerstroemia indica). These may serve merely as occa- 
sional food plants for the adults or as congregating places, but why 
the adults should congregate on them in large numbers, even in the 
presence of their favorite food plants, and not lay eggs, as has been 
observed in the case of the last two mentioned plants, we will not 
attempt to explain. That it does not always pay to "jump at con- 
clusions " or to make broad generalizations regarding the food plants 
of a polyphagous insect like the black fly is shown in the case of the 
orange jessamine. In the first place, it is a rutaceous plant, a citrus 
relative, and one would naturally expect it to fall into first or second 
class of food plants. That it is merely a supplemental host has been 
proved, not only by the repeated examination of a large number of 
plants, but also by attempting to rear the insect on it. Never has 
a single specimen of Aleurocanthus woglumi beyond the first instar 
been found on this plant, though egg spirals are laid in abundance 
on it and adults often collect in numbers on its younger growth. 
Although the larvae are able to attach themselves to the leaves, 
invariably they die and fall off before reaching the first molt. Hence, 
